EVEREST, MOUNT

a description of the attempts to climb mount everest, the highest known summit in the world, may be divided under three headings, the reconnaissance expedition of 1921, the first attempt to ascend the mountain in 1922 and the second attempt in 1924. previous attempts had been made to obtain permission to travel in that part of tibet and to explore and attempt to climb mount everest, but only the expeditions of 1921, 1922 and 1924 are dealt with here. the extraordinary advance in the relations be- tween tibet and the outside world were such that it was possible in 1920 to approach the tibetan govt. with every hope of success in obtaining from them permission to approach the mountain and explore its surroundings. as a preliminary, col. howard- bury, in 1920, visited phari dzong. his negotiations were suc- cessful, and in the winter of that year the first expedition was organised to reconnoitre and explore all the approaches to the great group and to make preliminary climbs on the mountain to ascertain the conditions and favourable points of attack. the reconnaissance expedition of 1921 this preliminary expedition carried out their work in the most complete manner the following summer. roads and approaches to the everest district, which are contained in the district of shekar and kharta sheka, were thoroughly explored and mapped. the approaches to mount everest on all its northern faces were thoroughly examined. relations were established with all the local authorities. this expedition was excellently con- stituted for the work in hand. under the leadership of lt.-col. c. k. howard-bury, d.s.o., the climbing party consisted of mr. c. h. bullock, dr. a. m. kellas, mr. g. l. mallory and mr, harold raeburn. maj. h. t. morshead, d.s.o., and maj. o. e, wheeler, m.c., went as surveyors and dr. a. m. heron as geolo- gist. mr. a. f. wollaston was doctor, naturalist and botanist. among them was one mountaineer and scientist whose name stands out pre-eminently in the exploration of the east central himalaya—dr. kellas. unfortunately dr. kellas died during the progress of the expedition’s march through tibet, and now lies buried under the fort of khampa dzong. the expedition was accompanied by two officers of the indian survey in maj. morshead and maj. wheeler, as well as by dr. heron, a repre- sentative of the geological survey of india. the rongbuk valley—the first object was to explore the rongbuk valley beyond the great rongbuk monastery. from there the mountaincering party pushed up the west rongbuk glacier, which descends directly from the northern faces of mount everest, but failed to find the true approach to the mountain up the narrow mouth of the east rongbuk glacier. this glacier was later on in the year surveyed by wheeler and the true approach was established. later, the expedition crossed over to the low-lying country to the east of mount everest at kharta sheka. | from there a pass was found named the lhakpa la, 22,000 ft., 1068 which led to the head of the east rongbuk glacier. from this point the mountaineering members of the party were able to trace the most likely line of attack on the mountain and actually mounted by difficult snow and ice slopes to a col on the main north ridge descending from everest, which they named the chang la or north col. by this time the season was late, the weather was breaking and no more work could be effected. the reconnaissance expedition had collected an immense amount of information and had mapped the country to the north of everest. the attempt of 1922 on the information and experience of the reconnaissance expedition, the second expedition to everest was organised, which was to complete the exploration of the group and to carry out the ascent of the great mountain. brig.-gen. the hon. c. g. bruce, c.b., m.v.o., was in command, with col. e. l. strutt as second-incommand. the climbing party consisted of mr. g. l. mallory, maj. e. f. norton, d.s.o., r.a., dr. t. h. somervell, dr. a. w. wakefield and capt. g. i. finch, who was oxygen officer to this pariy. dr. t. g. longstaff was doctor and naturalist. mr. c. g. crawford, capt. j. g. bruce, m.c., and capt. c. j. morris were the transport officers. maj. h. t. mors- head, d.s.o., as surveyor and capt. j. b. l. noel as photogra- pher completed the party forming the second expedition. choice of season.—it had been found necessary to make the attempt early in the year, as giving a better chance of good weather and of finding the snow conditions on the mountain more favourable-to an assault; but this early start also carried with it a great deal more exposure and, naturally, fatigue on the journey from darjecling to everest; for on this route not only are the passes which cut off the southern himalaya from the north to be crossed, but on the way a large number of high and exposed ridges have also to be negotiated. naturally, too, the outfit was much greater; and for the first time in the exploration of the mountains experiments were to be made in the artificial administration of oxygen as an assistance in counteracting the effects of low at- mospheric pressure. by the end of april 1922 the expedition was collected in the rongbuk valley and the base camp established within two miles of the snout of the west rongbuk glacier. an immense amount of stores of all descriptions had been trans- ported to this spot, employing some 350 transport animals. the transport problem.—lit is necessary at this point to explain how great is the problem of attacking such a mountain as ever- est. it differs immensely from an ordinary mountaineering ex- pedition, and besides the pure mountaineering technique which is required, many of the methods necessary for polar exploration must be put in force. besides, a large number of first-class porters are required owing to the immense amount of stores which must be moved to great altitudes. for them special clothing and food are necessary, which greatly adds to the difficulties of equip- ment. the expedition drew its porters mainly from subjects of nepal, belonging to a tribe known as sherpas. they are true tibetans, who in the course of generations have settled on the southern slope of the himalaya. they live in a steeper and slightly less elevated country than tibet, and are thoroughly suitable for the work; but among them there were also certain true tibetans of tibet. these men have proved through all the expeditions a great success. importance of the monsoon.—but the real problem is the race with the monsoon. this pcriod of time, from may 1 to early june, is the only suitable time for the attack on the mountain, and even this is dominated by the approach of the monsoon. up to the arrival of the south-west monsoon the whole northern slopes of the himalaya are swept by an intensely dry and cold wind. whil« these conditions continue, the mountains are safe if human beings can stand the terrible cold, immense fatigue and the dominating factor of low atmospheric pressure. when once the humid and warm southwest monsoon is established, the mountains are unapproachable, snows thaw, avalanches fall and progress is impossible. hence the great difficulty is an immense exertion to be undertaken in a short time. -camps established.—up the east rongbuk glacier camps were everest, mount established, from the base camp at 16,500 ft. above sea level to camp 3, four stages higher up, which was placed near the foot of the slopes leading to the chang la or north col. at camp 3 the advanced base of the expedition was established, at a height of 21,000 ft., and here were accumulated stores of every description for the attack on the mountain, with food supplies sufficient to last 12 europeans and 50 natives for one month. from here a high camp was pushed on up to the north col, which was suc- cessfully established in good weather. from this camp the first attempt without the assistance of oxygen was made. first assault on the afountain. —the four members of the party who were chosen for this effort, maj. norton, dr. somervell, mallory and morshead, set out from the north col. with great difficulty they established a camp at about 25,000 ft. on the sheltered side of the great north ridge which descends from ev- erest. this camp was carried up for them and pitched by the special sherpa porters. it is worthy of note that until this expedi- tion only once in the whole history of mountain exploration has a camp been pitched as high as 23,000 ft., the height of the chang la, and that was only for one night. the camp referred to was that of mr. meade’s expedition on kamet in garhwal. this camp at 25,000 ft. was occupied on may 19. the following morning three of the climbers, somervell, norton and mallory, continued their attempt on everest, morshead having to be left behind as he was suffering from frost-bite and exhaustion. the climbing party pushed on under trying conditions of wind and weather until they attained the height of 26,985 ft., the highest point yet reached by human beings. at this point their strength was so far exhausted as to make further progress unsafe, and a retreat was made. their descent was most toilsome and slow, but finally the camp at 25,000 ft. was reached, and morshead had to be conducted back from this point in bad weather to the north col. in traversing back from the gite on the face of the mountain,.an accident as nearly as possible occurred from a slip; but after a dramatic and exciting incident their laborious descent was continued, and finally, com- pletely worn out, they reached the camp on the north col at midnight. morshead was badly frost-bitten, and each of the other members of the party in a lesser degrce. first attempt with oxygen.—later, on may 25, a second at- tempt was made by finch and j. g. bruce, using the oxygen apparatus from as low down as camp 3. they were accompanied by naik tejbir bura, a young gurkha non-commissioned officer who belonged to capt. bruce’s regiment, the 6th gurkha rifles. this party followed on the footsteps of the previous one, camping, however, some 500 ft. higher, at a height of 25,500 ft. on the main ridge itself, their porters thus surpassing the efforts of the previous party. the porters returned to the north col, but the climbing party were caught that night in a furious hurricane and were camp-bound for two nights and a day. their experi- ences were most trying, and it is lucky that they ever survived that terrible exposure. the morning of the second day, the weather having calmed, they set out, using the full oxygen apparatus and employing the gurkha non-commissioned officer to carry spare oxygen bottles. on reaching the height of 26,c00 ft. this young man could pro- ceed no farther. the two mountaineers continued alone from this point, and before being completely exhausted reached a height of some 27,300 feet. their return journey, still using oxygen and picking up re- scrve oxygen supplies on the way down, was in great contrast to the experiences of the first party. they not only descended the mountain at good speed but continued from the north col or chang la directly down to the advanced base camp at camp 3. the expedition then returned to the base camp for rest, all members of the party being greatly exhausted. from this camp certain members of the expedition, including morshead, were obliged to return to india. third assault.—aa third attempt was organised, and the party left on june 3, consisting of finch, mallory, somervell, crawford and wakefield. finch shortly returned and joined the homing party. the remainder again pitched their camp at the advanced evolution base, and on the morning of june 7 attempted to reach the north col; but unfortunately they had been overtaken the previous three days by bad weather and heavy snow, and following the formerly used route to the north col they were obliged to traverse the snow slopes rendered extremely dangerous by the accumulation of fresh snow. they were caught in a great avalanche which swept down the face of the mountain side and carried down the whole of the party of 17 ropecl-in groups of four and five. two of these groups, one of four and one of five men, were swept over an ice clill some 60 ft. high, and only two out of the nine men thus carried away were saved. the leading rope, consisting of three climbers, crawford, mallory and somervell, was carried down for some 150 ft. by the avalanche and stopped well above the danger point without iniury to the climbers. this third attempt ended the expedition of 1922, which then, as a body, returned to india, having added immensely to the knowledge of the possibilities of further acclimatisation at high altitudes. tue attempt of 1924 the 1924 expedition consisted of brig.-gen. the hon. c. g. bruce, c.b., m.v.o., in command, and of lt.-col. e. f. norton, d.s.0., r.a., second-in-command. the climbing party consist- ed of mr. bentley beetham, capt. j. g. bruce, m.c., mr. j. de v. hazard, mr. a. c. irvine, mr. g. l. mallory, mr. n. e. odell and dr. t. h. somervell. mr. e. o. shebbeare was transport officer, dr. r. w. j. hingston, doctor and naturalist, and capt. j. b. l. noel was again photographer. this expedition was able to profit in a great number of ways by the experience of the two previous expeditions. leaving darjeeling at about the same time as before, it arrived a few days earlier at the same base camp at rongbuk. its transport had been improved and in- creased. unfortunately, during the march up, gen. bruce had been obliged to return to india owing to illness, and his place was filled by norton. bad weather at base camp.—on arrival at the base camp, every effort was made to establish a line of intermediary camps between the base camp and camp 3 with the greatest possible rapidity; but the expedition was overtaken by hurricane after hurricane during the month of may, at a time when fair weather is ordinarily to be expected. the temperatures experienced were very much lower than in 1922, and it was very soon discovered that a low temperature, high wind, hard work and a low atmos- pheric pressure together are enough to wear out the very strong- est constitution in a very short period. so for some three weeks the expedition struggled in a con- tinuous battle to establish not only the camps on the line of com- munication but also the alpine base on the summit of the north col. this terrible fight against the elements, occasioning several returns for recuperation to the base camp, not only delayed the expedition very much indeed but reduced their strength and that reserve of power which is necessary for the fina] great assault the great test of all; nor at high altitudes can that lost strength be ever adequately regained. new route ta north col.—the route that it was necessary to utilise between camp 3 at 21,000 ft. and the north col camp at 23,000 ft. was far steeper and more difficult than that of 1922; but it had the advantage of being safe from the avalanches, which render the easier slopes of the 1922 route most dangerous after such weather as was experienced in this season. but it was on this route that another accident almost occurred. after the new difficult route to the north col had been forced by nor- ton, hazard led the first party of porters and established the camp on may 22. on the following day, on his descent from the north col camp to camp 3 in bad weather, it was discovered that four porters had remained actually on the north col itself. a hurricane that night and the following day prevented communi- cation with them, but on the day succeeding, norton, somervell and mallory formed a rescue party to extricate these men from their awkward position. this they successfully accomplished after a most dramatic incident, two of the porters, when crossing a dangerous face, to69 slipping down and being brought up at the edge of an ice cliff. from this position they were rescued after a very severe strug- gle. all members of the party were at this time terribly worn by exposure to the low temperatures and gales, the temperatures registered even at camp 3 being as low as —23°f. after this, the expedition retired to the base camp for a complete rest. the members of the party and porters were all completely worn out. norton led his party down to the monastery at the mouth of the rongbuk valley, presided over by a remarkable lama or buddhistic priest, aman in whom every buddhist mem- ber of the party placed absolute faith. here a service was held, the lama blessed and encouraged the men, and then, when morale was established, norton, reorganising his party, led the whole expedition back again to the advanced base camp 3. ifopes were now raised by the splendour of the weather. with reorganised plans, on june 1 camp 4 was re-established on a greater basis than ever, and from this camp the climbing party started the real assault on the mountain. there were few porters left who were fit to make such an immense effort as was required of them, and therefore several attempts were made by parties of two climbers, assisted by whatever porters were available. mallory and j. g. bruce pitched camp 5 at 25,000 ft., but owing to the exhaustion of their porters were obliged to return. they were followed on june 3 by norton and somervell, who, passing through them, actually pitched a camp at 26,800 ft. elevation, men having been found fit enough to carry loads with- out the assistance of oxygen to this great height. from this point, with the greatest pain and trouble, somervell and norton reached a height on the following day of 28,200 ft.; they again descended to the north col. somervell had been working under disadvantageous conditions, suffering terribly from a high alti- tude throat. so dry and parched does one’s throat become in this intensely cold and dry air that it forms more than an incon- venience, even a danger. norton had been fit and well, but the following morning awoke absolutely sightless from snow blind- ness. an unforgettable episode occurred the following morning when norton, stone blind, was taken down that steep and diffi- cult clescent by hingston and hazard. the last attempt.—there was still one more attempt to be made by mallory and irvine. there had been defects in the oxygen apparatus and but little oxygen was now available. they were assisted by a supporting party consisting of odell and hazard, who accompanied them to the 25,000 ft. camp. this point, on june 6, they left with porters, who again carried loads for them to 27,000 feet. on june 8 they left camp 6, the highest camp, for their attempt. odell on that morning arrived, accord- ing to arrangements previously made with mallory, at this high- est camp, to watch their progress and report on it and to take such steps for their comfort as were considered necessary. he caught a glimpse of the climbers high up on the mountain side for a short space of time; the mists blew across and he saw them no more. returning to camp 4 he awaited their return, but on the following morning, sceing no signs of them, he searched with signal and magnesium flare the whole hillside without effect. on june 1o, for the third time, he mounted the slopes to 27,000 ft.—in itself an unprecedented effort—but could find no signs of mallory and irvine, and, communicating with norton, evacuated the mountain. thus stands the battle with everest up to 1926. unfortunate- ly, the expedition also lost one young gurkha non-commisstoned officer from over-exposure, and one tibetan follower from frost- bite and pneumonia. at the base camp stands a monument to those who gave their lives in this great attempt. bibliogr oa —c. g. bruce, the assault on mount everest, 7922 (1923); e. f. norton, the fight for everest, 1924 (1925). see also the ‘alpine journal (1922~ 5) and the geographical journal, incl, prec. roy. geog. soe. (1924-5). (c..g, b*) evolution (sce 10.22).—the topic of evolution is a very wide one. in its broadest sense it denotes little more than grad- ual change, as is indicated by the common french equivalent transformisme, in a somewhat more restricted sense it implics orderly change, while certain authors wish to combine it with 1070 orderly and progressive change. the two fields, however, in which it is most often applied are those of cosmic and of organic evolution, the former dealing with the development of stars and stellar systems, the latter with the changes undergone by life upon this planet. here, only the topic of organic evolution will be discussed. i. general survey organic evolutton—there are three quite distinct angles from which the subject can be treated. in the first place, there is the question of the fact of evolution: has organic evolution occurred or has it not occurred? secondly, there is the method of evolution: by what mechanism has evolution been brought about? and thirdly, there is the course of evolution: granted that it has occurred, what were the main results of the process? the evidence the evidences on the first point are well known. they are chiefly drawn from the facts of comparative anatomy, of em- bryology, of geographical distribution and of palaeontology. palaeontology.—the last, or the history of life as revealed by actual fossil remains of organisms in the sedimentary rocks, affords the most direct evidence, since we find that many past organisms are now extinct, and that there are frequently to be traced long evolutionary chains, leading up from primitive ex- tinct forms to specialised modern types. embr yology.— that of embryology is, however, equally impor- tant. the majority of animals run through, in the course of their development, stages which resemble other organisms. the fact that a fowl or a man passes through a stage in which its organisa- tion is essentially like that of a fish is meaningless, save on the assumption that land vertebrates originally evolved from fish- like, aquatic ancestors. distribution of animals.—the distribution of animals and plants over the earth’s surface is, further, such that it cannot be explained except by assuming that evolution has occurred. if certain types have had their origins in certain areas, and have then spread thence, the facts are intelligible, but not otherwise. in the same way, the fact that oceanic islands contain but a very limited fauna and flora, and that, in oceanic archipelagoes, the types of animal life are often represented by different species on each different island, is readily explicable on the idea of chance spreading, followed by isolation and consequent evolutionary divergence. comparative anatomy. —the evidence from comparative anat- omy, though perhaps the most indirect, is equally strong, and was historically the first to attract attention. when we examine a series of, say, vertebrates, we soon perceive that a common general plan runs through them all, in spite of great differences in their various modes of life. the same is true for each particu- lar organ. the hand and arm of man, the foreleg of a dog, the wing of a bird, the flipper of a whale—all these, and indeed the fore-limbs of all terrestrial vertebrates, show the same essential plan, though often much modified to suit the exigencies of the animal’s particular mode of life. it must not be supposed that no other general ground-plan can exist: far from it. the insect or the crustacean is built on a wholly different general plan, and the special plan of its limbs is entirely different from that of the vertebrate limb. it is very difficult to explain these agers except on the theory of evolution. vestigial organs.—the conclusion is strengthened oe the ex- istence of vestigial organs (often called rudimentary organs), which are useless to their possessor, although corresponding (homologous) organs in other specics are of service. the vestig- jal hair on the surface of the human body affords one excellent example, while another is provided by the wholly useless rem- nants of limbs in various snakes. often vestigial organs are re- capitulatory as well, being better developed in the embryo or young than in the adult (hair and tail of man, teeth of certain whales, etc.). natural selection.—the evidences for evolution having taken place were first cogently marshalled by charles darwin in the evolution origin of species (1859). no satisfactory alternative explanation of the data he adduced has ever been advanced, and the fact of evolution has passed beyond the realm of discussion. darwin, however, accomplished much more than this. he also advanced a theory as to the method of evolution, and one so reasonable that it could be and is still widely held by scientific men. this was the theory of natural selection. he assumed as a fact the existence of variation, showed the universal presence of a struggle for existence due to the invariable birth of more young than can come to maturity, and then pointed out that this would inevi- tably lead on the average to the survival of those that were best fitted to survive and so to evolutionary change and progress. by so doing at one stroke he cut the ground from under the feet of those who, like paley, argued that organic adaptations were evidences of conscious design. sexual selection.—he also advanced the subsidiary hypothesis of sexual selection to account for the development of special sexual adornments employed in courtship or display. here the underlying idea of the automatic selection of some types and the failure of others remains the same, but the selective agency is now the mind of the opposite sex; and, further, the sclection may be between rival males as concerning success in mating only, and the characters selected may not only have no utility in relation to the ordinary business of survival, but in extreme cases may handicap their possessor in the struggle for individual existence. however, the biological advantage gained by being selected as the father of offspring, especially in polygamous species, may be so great as to compensate for disadvantage in other directions. this theory has been much criticised, but has now, in somewhat modified form, been shown to rest on a firm basis. darwin also, in part, adopted the second main theory of the method of evolution, that of lamarck, by assigning some weight to the direct effect of the environment and to the effects of use and disuse. three other main types of hypothesis to account for evolution- ary change have also been advanced. the first has been styled orthogenesis. it is frequently observed by palaeontologists that evolutionary trends in particular directions can be traced in series of fossils. the theory of orthogenesis assumes that the straight course pursued by such evolving types is due not to moulding, direct or indirect, from without, but to inner neces- sity, the hereditary constitution of the race unfolding and chang- ing according to predetermined laws. next, there is what may be called the crude theory of mutation, according to which species may enter upon a mutating period, and rapidly throw off a num- ber of new and markedly distinct types, which may often be merely new without being better or worse suited to the environ- ment. finally, there is the view urged by lotsy, that new types arise by recombination of characters after crossing. we know that when very <listinct types are crossed and are fertile, there is (as demanded by the mendelian theory) great diversity among their offspring from the second generation onward. lotsy imag- ines that very wide crosses may occur, with enormous resultant variation, and that this variation is the sole raw material of evolutionary change. we may call this the recombination hypothesis, since it supposes that evolutionary novelty is due to new combinations of old characteristics. the last three theories emphasise the force of inner variation as against that of outer environment. the mutation and the recombination theories think of the process as occasional and random, that of orthogenesis as continuous and directional. the other two lay greater stress upon the environment. but whereas the lamarckian theory assumes a direct effect of the en- vironment, the hereditary constitution responding like wax to outer changes, the effect in darwin’s theory of natural selection is only indirect. the source of variation is here in the hereditary con- stitution and it occurs in all directions; the environment is exert- ing a constant pressure and ensuring that only the “ right ” variations shall survive. [t cannot be said that the problem is yet by any means solved. in particular, the first origin of variations remains one of the great problems of biology. it would appear, however, that all evolution theories can contribute something of value, although an adjust- ment of the theory of natural selection to a modified mutation theory will probably account for the majority of the facts. heredity in the light of mendclism—we must remember in any case that any accurate knowledge of the processes of heredity was denied to darwin. not until the rediscovery of menclel’s work in 1900 was it possible to push forward along this path. we now know that the great majority of inherited character- istics are dependent upon the presence of definite units (factors or genes) present in the hereditary constitution; and that these are lodged in a definite proportion and definite arrangement in the chromosomes which are transmitted from parent to offspring in the gametes (see cyrology; genetics; mendelism). nor- mally, these units remain constant, and resist change with ex- traordinary resistance. occasionally, however, they have been found to change apparently spontaneously (though this, of course, only means that we have not yet ascertained the cause), and, once changed, to remain constant in their changed form. such changes are now generally known by the name of muta- tions. it is important to note that mutations of this type may be of any extent, some causing marked, others very slight, changes and the generally accepted view now is that mutations of slight extent afford the major part of the raw material of variation; natural selection may then act. it is a curious fact that the “ mutations ” of the evening primrose adduced by de vries, in the earliest presentation of the pure mutation theory, have turned out to be, some of them, not mutations at all, others mutations of a different and rarer type (due to subtraction or addition of whole chromosomes). there is further evidence that in some apparently rare cases mutations may be caused directly by changes in external con- ditions; so that in respect of these, a modified lamarckian theory will hold. melanism in moiths—the latest and most satisfactory evi- dence on this matter, the production of melanism in moths by treatment with the metallic salts found deposited by smoke in industrial areas (j. w. h. harrison and f. c. garrett, proc. roy. soc., 1926) indicates that the induced hereditary change is not directly adaptive, and, once produced, remains constant and is inherited according to mendel’s laws—in other words, that such changes are induced mendelian mutations. on the other hand, there is as yet no evidence which has satisfied the majority of biologists that the effects of use and disuse are ever directly inheritable. as regards orthogenesis, there is no doubt that beautiful series of fossil forms, each tending in a par- ticular direction towards specialisation for one particular mode of life, may be found. but there is no evidence whatever that these are to be accounted for by some inner necessity for deter- minate variation in a particular direction, and not rather by gradual improvement at the hand of natural selection. in addition, however, to such series (which obviously run counter to lotsy’s theory of recombination) detailed studies of variation among existing species bring to light numerous char- acters which appear to be of no biological advantage or the re- verse to their possessors, and are most readily to be accounted for as due to random mutations. finally, in some cases, espe- cially among plants (as roses, willows, etc.) enormous variability is found combined with evidences of hybridity. here it appears almost certain that evolution by hybridisation and recombina- tion has been effective. the most plausible view as 1o the mech- anism of organic change (although it must again be emphasised that there is as vet no unanimity on the matter) is therefore somewhat as follows:— a mechanism of organic change.—the raw material of evolu- tion is provided chiefly by variations in the form of factorial or point mutations. some of these may be directly caused by changes in the outer world; but even when this is the case, there is no reason that they should be adaptive—sometimes they may be, sometimes they may not. others, probably the majority, are not as yet to be traced to definite external causes; they are “ spon- taneous ”’ (as in another field of science are the disintegration changes suffered by the radioactive elements). some of these 1071 come under the action of natural selection: the biologically fa- vourable benefit their possessors and are preserved, the biologi- cally unfavourable are weeded out. still others appear to be neither favourable nor unfavourable; and their survival is a mat- ter of accident. it is further clear that if an organic type pos- sesses a hereditary constitution of a chemically definite nature, this will restrict the possible changes which it may undergo— in other words, will make variation, within certain wide limits, determinate. to this limited extent the principle of orthogenesis will be at work. finally, we obtain evolution by recombination in the comparatively rare cases in which two or more distinct races or species can cross and produce normally fertile offspring. one thing at least can be stated to-day with assurance, and that is that the mechanism of evolution is not simple, and that no single one of the various theories previously advanced will by itself prove to be sufficient. creative evolution and climatic changes.—in considering the evidence bearing upon orthogenesis, biologists have been forced to take account of the geological evidence bearing upon past climates. asa result, opinion is inclining more and more to the view that the marked bursts of “ creative ” evolution, when new types are rapidly and abundantly produced, as with the mammals at the very beginning of the caenozoic epoch, are to be corre- lated with pronounced changes in climatic conditions. when a single pond dries up, the species inhabiting it simply become dis- persed to other neighbouring ponds. but when a whole area of the world’s surface becomes progressively drier or colder, the life which inhabits it must either change or die. the detailed working out of this difficult subject of past climates will be of great importance for a study of evolution. we now come to the third main heading under which we can study evolution. taking for granted both the fact of its occur- rence, and the existence of some sufficient mechanism, we can seck to discover what has actually happened, and whether any gencral principles or laws can be traced in the process. the fossil record —we are at the outset placed under a grave handicap, in that our most trustworthy and direct source of evi- dence—that from fossils—is only available for a limited part of evolutionary history. the earlier fossil-bearing rocks have in part been denuded away (to be carried down to the sea and deposited once more as rocks of a later age), or else so much al- tered by the heat and the pressure to which they have been sub- jected in the course of geological time, that they are completely metamorphosed, and their fossil record obliterated. opinions differ as to the proportion of the geological record which has thus been destroyed, but at a very conservative estimate it comprises at least half the time during which life has existed upon the earth. as a result, when the earliest richly fossiliferous rocks are exam- ined, they are found already to contain representatives of most of the main groups of animals. with regard to the vertebrates, however, this is luckily not the case. they evolved late; and the rocks provide us with an excellent record of the evolution of their main groups (see palaeontology). in addition, however, the indirect evidences of comparative anatomy and embryology do permit us to draw a number of broad conclusions concerning the other groups with a reasonable degree of certitude. when we assemble and analyse the evidences drawn from every possible source we find that we can obtain from them a body of important general principles concerning the direction which evolution has actually pursued. these principles appear to hold good equally well for all the main groups of animals in which they can be checked and not only for vertebrates. lower and higher types.—in the first place, when a higher type evolves from a lower, it is usually found that this does not involve the total disappearance of the lower type. commonly, representatives of the lower type survive, but the total number of its species is reduced, and the survivors are often smaller in size and lead less conspicuous lives than when the type was in its prime. the classical example is afforded by the reptiles and the mammals. the farmer with their “ cold blood ” and ab- sence of placenta and of milk are definitely of lower organisation than the latter. in the mesozoic epoch, they became the dominant 1072 group of vertebrates, and branched out into various striking types—gigantic herbivores, carnivores of corresponding bulk, flying forms, marine fishlike types and so forth. by the onset of the caenozoic period, the mammals had become dominant; the reptiles still survive but only in the shape of crocodiles, tor- toises and turtles, snakes and lizards. similar survival of ‘‘ lower ”’ types, but in duced numbers and reduced variety, alongside of “ higher ” types is also seen when we look at the evolution of human inventions, an obvious example being afforded by the survival of pack transport and horse-drawn wheeled vehicles after the introduction of mechani- cally-propelled vehicles. a consideration of the causes operating to produce such effects with human inventions often clarifies the causes of similar survivals in biological evolution. directional change.—as a result, we find that at any given moment the organic world provides us with a selection, not merely of the latest-evolved types, but of most of the main types which have ever come into being. when, on the other hand, we consider the latest types only—in other words, the upper level reached by life instead of its whole range—we are enabled to trace a definite directional change in evolution. there has been a tendency to produce types which can respond with greater precision to changes in the environment, which have greater control over external objects, are increasingly inde- pendent of the environment, and more self-regulatory. these tendencies are revealed in various concrete ways. the efficiency of the various organs of animals has become greater. sense organs come to have greater range and greater accuracy; one has only to compare the nervous system—brain, spinal cord and nerves—of a mammal with the nerve-net of a jelly-fish and this with the nervelessness and almost total absence of co-ordina- tion in a sponge to have the advance as regards conduction and co-ordination very forcibly brought home; and equally striking examples could be drawn from other systems, such as the loco- motor, the skeletal, the blood-circulatory or the digestive. a very striking step was that taken by the birds and mammals alone among all organisms—the acquisition of special machinery per- mitting the body temperature to remain constant (‘‘ warm blood ”’); this permits the general activity of the organism to re- main at the same level in spite of great changes in outer tempera- ture, whereas that of all other organisms rises and falls with the temperature like an ordinary chemical reaction. general and special organisation.—efficiency of machinery for control and self-regulation may be improved in two main ways—in relation to the organisation as a whole, or in relation to a particular mode of life. for example, the general organisa- tion of the mammalian type is an improvement upon the reptil- ian. on the other hand, the organisation of the horse is an im- provement upon that of the early mammals when considered in relation to a cursorial and vegetarian existence, that of a whale in relation to a marine existence. but it cannot be said that in general organisation either horse or whale is superior to the other. this latter type of improvement we speak of as specialisation, the former as improvement of general organisation, or more succinctly as biological progress. biological progress involves all- round advance; but specialisation, which is by definition speciali- sation in regard to one particular direction and mode of life, in- variably involves a sacrifice of possibilities in other directions and for other modes of life. the horse, by the very fact of being adapted to grass-cating, is cut off from all carnivorous diets; the whale, through being so thoroughly adapted to life in water, is debarred from the possibility of hfe on land or in the air. sometimes the adaptation is such a limited mode of life that the sacrifices appear to outnumber the gains. we then speak of degenerative evolution. this is best seen in animals which have exchanged a free-swimming for a sessile existence, or those which have taken to parasitism. it should not, however, be forgotten that degeneration is always a form of specialisation. even the most *‘ degenerate ” parasite is beautifully adapted to its mode of life in its mechanisms for passage from host to host and in its arrangements for maintaining itself unharmed within a particular part of its host’s body. evolution specialisation.—further, the evidence seems clear on one im- portant point—no highly-specialised form appears to retain the possibility of giving rise to types specialised in some quite other direction, or to a type which shows a general advance in organi- sation. it was among the most generalised fishes that the an- cestors of land animals took their rise; and the ancestors of man are not to be sought among any of the specialised groups of mammals like ungulates, carnivores or the like, but in the hum- ble and generalised insectivora. in other words, the sacrifice involved by specialisation is not only a morphological one; the special improvement involves also a sacrifice of general evolu- tionary possibility. as each new type comes into being we find in general the fol- lowing series of events. there is first a considerable period during which the new type is not fully perfected; its representatives remain small in size, few in numbers and in kinds, and of little importance as compared with the dominant type from among whose more primitive members they have sprung. then, com- paratively suddenly, the new type ousts the old from its position of dominance. this is well exemplified by the early mammals which existed during the age of reptiles and their sudden rise to supremacy at the close of the secondary period; or by the long period during which primitive man existed at a low stage of attainment, prior to his quick rise to biological dominance in the lust 10,000 or 20,000 years, or—to utilise our example from hu- man inventions once more—by the early decades in the history of the motor-car, when it was regarded as either a joke ora nuisance, before its sudden rise into general use. once the new type becomes well established, it usually evolves into a number of specialised branches, together with other branches which remain relatively primitive and generalised. this spe- clalisation of a group into a number of adaptive lines is usually known by osborn’s term of adaptive radiation. it is beautifully illustrated in the fossil history both of the reptiles and of the mammals (and again in the origin of numerous divergent types of motor vehicle as soon as the motor type came into favour). progress from lower to higher—it remains to ask whether one type can legitimately be called “ highcr ” than another, whether the term “ progress ” can legitimately be used for any purely biological process, since such terms involve the idea of value. types undoubtedly differ in regard to their degree of efficiency, self-regulative capacity, etc.; and thercis also undoubt- edly a general directional trend to be traced in the evolution- ary history of life as awhole. it is further found, however, that this trend is in the general direction of producing qualities and characteristics which are regarded as valuable by us (control, efficiency, independence, etc.), and that the difference between what are customarily called lower and higher organisms does again correspond with a difference in regard to qualities which do seem valuable to us. in other words, the terms high and low as applied to organisms, and biological progress as applied to a certain direction of evolution are perfectly legitimate. conclusion.—in conclusion, it should be remembered that the fact of biological progress, of a steady trend of the upper level of life in an upward direction, by no means implies, as is sometimes stated, the existence of an internal “ urge,” or of a non-natural guiding force; nor need we assume any purpose in the process. the matter is on a par with the question of purpose in tegard to specific adaptations, which were taken by paley as definite proofs of purposeful design by a personal designer. darwin, however, pointed out that the purpose here was only apparent, and that adaptations could be satisfactorily accounted for by the non-purposeful automatic working of natural forces. precisely the same is true of the apparent purposefulness re- vealed in biological progress. on reflection, it, too, is seen to recelve a satisfactory explanation on the same darwinian prin- ciples. the struggle for existence being as keen as it is, any ad- vance, whether specialisation along a restricted linc, or progress in general organisation, will be a biological advantage. purpose is a purely psychological category, and the term should only be used when other explanations can be excluded. it is, however, important to notice that, with man, purpose has evolution come to have evolutionary significance. any future progressive evolution of the human species (see eugenics) or of human in- stitutions must inevitably depend, in greater or lesser degree, upon true purpose; and this itself is a biological advance, for purposive planning is both more direct and less wasteful than the pseudo- teleological methods of natural selection. (j..5. hi) ii. evolution and comparative anatomy the science which is concerned with the resemblances and dif- ferences which exist between the bodily structures of animals, was cultivated by the zoologists of the 19th century with such success that by 1870 the structure of representative members of all the greater groups of vertebrates was known, and even the invertebrate groups were well understood. the body of facts so brought together forms the foundation of the theory of organic evolution. it established that the whole series of living animals, some 2,000,000 in number, resembled one another in such a way that their organisation could be referred to a small number of fundamental types, sharply marked off from one another, and not connected by any animals of intermediate structure. the more important of these groups are the protozoa, porifera, coelenterata, platyhelmia, chaetopoda, arthropoda, mollusca, polyzoa and chordata, whose characters and mutual relation- ships are well explained in the zoological articles of the ecyclo- pedia (see 28.1033 esp.}. the general acceptance of the truth of the doctrine of evolu- tion led to a great deal of work on comparative anatomy, with the intention of displaying the steps by which the structure of the higher animals had arisen from that of lower forms. it was soon realised that a continuation of this work resulted merely in the accumulation of details, which although sometimes inter- esting, could not bring about any important changes in the con- clusions which had already been reached. two hes of research appeared open to the morphologists of 1870; they could add the investigations of function to that study of pure form which was their selected field, or they could determine the actual mode in which the structures they described came into existence during the embrvological development of an animal. study of embryology.—the problems raised by an attempt to relate the structure of an animal to the functions performed by its organs are, except in specially simple cases, of great difficulty, requiring resources of physics and chemistry which were not available in 1870; thus it was to the study of embryology (q.7.) that the majority of morphologists turned. their work soon led to results which revolutionised the whole subject, placing many homologies between the parts of different animals, which had previously been disputed, on a firm foundation and introduc- ing the element of succession of events in time. but embryology in its turn has reached a stage in which the new work ts concerned solely with detail, and no fundamental new facts are likely to be discovered by the old methods. there is however another way in which the time element can be brought into morphology; study of the remains of fossil animals has, of late, solved some out- standing problems amongst vertebrates and has revived interest in the whole subject. experimental work.—the most promising mode of attack is, however, through experiment. it is possible to interfere with the development of an animal: by altering the rate at which it pro- ceeds, by cooling or by chemical means; by the removal of the primordium of one of its organs; by transplanting a developing eye or ear into a new region of the body, or even by grafting halves of two different species together. work of this kind is being very actively carried on, especially in the unites states of america, and it has already revolutionised our outlook on morphology. the study of evolution, and of the causes which have brought it about, is not now fashionable. all zoologists regard the truth of the doctrine as established more by the patent incredibility of other explanations than by direct evidence; indeed only the study of palaeontology (q¢.v.) leads to a vivid realisation of its truth and of the details of the process. thus zoologists, being no longer compelled to concern themselves with the truth of a fun- 1073 damental principle, have been free to devote their attention to those problems which gave promise of rapid solution. at present it is difficult to design and carry out experiments whose direct object is the establishment of the factors which bring about evolutionary changes, because the whole subject 1s overlain by a mass of theoretical conclusions based entirely on the examination of observed facts, whilst many aspects of the subject which are quite fundamental have never yet been ade- quately explored by an experimental method under controlled conditions. mendelism (q.v.).—the rediscovery in 1900 of mendel’s principles of heredity showed that the assumptions made by the earlier naturalists, and even the conclusions reached by statisti- cal methods of investigation, might have no validity so far as the individual was concerned, and emphasised the necessity of a renewed and rigorous investigation of that heredity to which every animal owes its morphology. but this work, as it has been carried on, especially by the school of morgan, is itself morpho- logical, it relates the structure of an adult animal to that of the chromosomes contained in the nucleus of the zygote from which it arises. the problem which now confronts morphologists is to discover the mode in which the “‘ genes ”’ function, that is, the nature of the factors which so control development as to deter- mine the final structure attained by the animal. this problem is being attacked by the methods of experimental embryology, which are leading to a better understanding of the meaning of the facts of comparative anatomy. thus, by their early work, comparative anatomists established the prima facie case on which our belief in the reality of evolution rests, whilst by the work that they are now carrying on they hope in the end to come to an understanding of those forces which underlie the phenomenon of evolution. birliography.—w. bateson, material for the study of variation (1893); j. w. jenkinson, experimental embryology (1909); d'arcy w. thompson, growth and form (1907); e. s. russell, form and function (1916). (d. m.s. w.) iii. the palaeontological aspect the law of evolution, especially as applied to human origin, has again been challenged in the united states by adherents of religious bodies who are described as fundamentalists as distinguished from modernists (see fundamentalism). the movement is based on a revival of the literal interpretation of creation as described in the book of genesis, largely under the eloquent leadership of the national politician, william jennings bryan. evolution is characterised as an unfounded hypothesis, unsupported by evidence, subversive of youthful morals, and, therefore, a menace not only to religion but to the state. bryan and other lay and clerical opponents of evolution sus- tained their course by direct citations from dr. william bateson’s toronto address to the american association for the advance- ment of science (1921), “ evolutionary faith and modern doubts,” which supported the law of evolution and, while com- pletely negative as to the causes of the origin of specics, served to clear the biologic atmosphere and to intensify research for veritable causes. © palaeontologic aspects of the theory of organic evolution zoological researches on variation, selection and the origin of species, up to the year 1926, have ended in a series of negative conclusions and opened the way to consider the new light thrown on the problem of adaptation by palaeontologic research. in such research we may sharply distinguish between the illumina- tion of the law of evolution as a universal principle of plant and animal descent and the light which palacontology throws upon the causes of evolution and, consequently, on the older theories of causation. (1) palaeontology substantiates natural selection in its larger meaning but deprives it of its creative or originative power. (2) palaeontology gives an equally strong negation to lamarckism in its creative sense of immediate inheritance in course of present time. (3) palaeontology presents an equally - strong front against discontinuity and mutation, or sudden sal- 1074 tations in mechanical characters, and substitutes an absolute, unbroken continuity in secular evolution as in growth. material observed.—in palaeontology, however, the field of observation is chielly limited to the adaptations of the hard parts preserved in a fossil state, to the relations of function and form, to the adaptation and development of new proportions (allome- trons) in mechanical structures—adaptations which are prima- rily biomechanical. thus while palaeontology negatives both selection and lamarckism in biomechanical evolution, it has its strict limitations, it throws no light on the possibility of discon- tinuity or mutation in biochemical or biophysical evolution. there are grounds for believing that saltation, mutation and other forms of discontinuity, such as may frequently occur in adapta- tions primarily biophysical and biochemical, immunity and non- immunity, fertility and non-fertility and interbreeding, physical reactions to temperature, atmospheric pressure, etc. as the unique result of palaeontological research we perceive evolution as a secular phenomenon, a process of the ages which, measure either by geology or by the radium content of the rocks, is infinitely slower than either lamarck or darwin con- ceived. lamarckism in part holds true as a cause of secular evolution, just as darwinism (i.e., survival of the fittest) holds true as a potent cause of secular evolution. on the other hand, palaeontology denies absolutely the origin of species according to the original conceptions and literal interpretations of cither lamarck or darwin. in claiming that all that is acquired is transmitted, lamarck was over-confident, as darwin was over- confident in claiming that every variation, however slight, may favour the chance of survival. the second unique result of palaeontological research is to transfer from the field of reason, imagination and speculation to the field of direct observation the whole question of the modes and methods of evolution and the whole problem of the manner in which new specific adaptations originate and of the details by which new biomechanical species are constantly created. we refer to such biomechanical adaptations as the elongated neck of the giraffe, the classic case cited by lamarck and darwin, the highly complicated mechanical evolution of the teeth, the origin and development of horns and of defensive armature. the record of the rocks.—in the 60 years since 1865 some palae- ontologists have been speculating, while others were quietly devoting themselves to gathering harvest after harvest of facts about the modes and methods of the origin of species. the palaeozoic rocks of eastern america afforded iiyatt (1866) oppor- tunities similar to those enjoyed in europe by waagen (1869) and neumayr (1871) of observing in closely successive and con- tinuous stages (mutations of waagen) that the old barriers be- tween “ species’ as conceived by lamarck and darwin are entirely broken down and one specific stage merges into the next without a break; in this respect evolution appears exactly like growth. in vertebrate palaeontology finely successive fossil hori- zons in the arid western states of america yielded osborn and others closely continuous stages in all the hard parts of many lines of mammalian descent, especially horses, rhinoceroses and titanotheres. ; tuee creative origin of species thus between 1859 and 1926 the “ origin of species ”’ has be- come an entirely different problem from that conceived of by darwin or, in fact, by any other zoologist, because our knowledge of what constitutes a species is entirely different. as palaeon- tologists we are observing the initial and terminal phases of a con- tinuous creative evolution and udauptation of ihe germ plasm, be- cause palaeontology forces upon us this new creational definition and conception of evolution, namely, of a continuous creative unfolding of life fitted to a continuously changing environment. it is remarkable that through palaeontological research the original latin word ‘ evolution ” becomes inadequate and the old sanskrit word v kur reasserts itself. create (lat. creafus, make, create, akin to gr. xpatvew, com- plete, skt. vkar, make.) 1, trans. to bring into being; cause to ex- ist. 2. intrans. to originate; engage in originative action. hvolution this new creative definition of evolution expresses the two new principles of evolution discovered in palaeontology, namely, the principle of continuity and the principle of rectigradation, the one a denial of mutation in biomechanical evolution, the other a denial of for/uzty in biomechanical evolution. species and adapiations—it appears through the study of continuous scries of invertebrate and vertebrate fossils that “species ” and “ adaptations ” are synonymous terms, as may be clearly seen in the history of these two terms, from aristotle to linnaeus.! the origin of species and the origin of adaptations are phenomena of the same significance, for every “‘ species ”’ is an ensemble of countless “ adaptations ’? in various stages of rise and decline. what aristotle (300 n.c.) called an adaptation, linnaeus in 1758 called a species. when aristotle in his //istory of animals and his physics debated the natural causes of adap- tations he had in mind the same structures and functions as those which linnaeus used in defining his species. tor example, the celebrated “ survival of the fittest ’ passage in aristotle’s physics (taylor’s translation) :— | what, then, hinders but that the parts in nature may also thus arise? tor instance, that the teeth should arise from necessity, the front teeth sharp and adapted to divide the food, the grinders broad and adapted to breaking the food into pieces. . . . it is argued that where all things happened as if they were made for some purpose, being aptly united by chance, these were preserved, but such as were not aptly made, these were lost and still perish, according to what empedocles says concerning the bull species with human heads, ... nature produces those things which, being continually moved ae a certain principle contained in themselves, arrive at a certain end. for example, again, linnaeus (1758) defines the anthropoid ape known as the orang:— simia: dentes primores 1v., approximati. lantari solitarii, longiores hinc remoti. jafolares obtusi. cauda nulla: simiae veterum. seven principles of origin baldwin thus defines the word “ principle ” in its bearing on science in general :— principle (lat. principtum, commencement, beginning: trans. of gr. eox#, beginning, authority): ger. princip; fr. principe; ital. principio. scientifically, it is the law through which a diversity of facts, otherwise unrelated and unexplained, are classified and interpreted: opposed to datum, brute fact or “ mere '’ fact. .. . greek philosophy began with the search after the principle in the literal sense: that original reality (a) from which other things are derived, and (6) out of which they consist. in the sense («) it was implicitly or explicitly dynamic, a force, a causal power; in the sense (}) it was static, an element of subsistence. the first meaning led up to aristotle’s form eiso0s as a principle; the second to his matter ua. the seven principles —briefly, the first of these subsidiary principles discovered and formulated in zoology as confirmed and amplified in palaeontology are five in number: first, the prin- ciple of individual adaptation or reaction to changes of motion or function which invariably precede changes of form, as first observed by aristotle and finally confirmed by the experi- mental observations of arbuthnot lane and felix reg- nault; second, the aristetle-lamarck principle of development through use, of degeneration through disuse, of balance through unchanged or static function. these two principles were under- stood and expressed by goethe in the pre-lamarckian year 1784 when as a brilliant novitiate in human and comparative anatomy he was on the very threshold of evolution:— thus by the animal’s form is its manner of living determined; likewise the manner of life affecteth every creature, nloulding its form. third, the ontogenetic principle by von baer in embryology and hyatt in palaeontology, of acceleration or the hurrying forward of characters in development and in evolution, and of retarda- tion or the slowing down of characters, according to juvenile or adult needs in the struggle for existence; fourth, the empedo- cles-darwin principle of individual and racial struggle for exist- ence and individual and racial survival of the fittest; fifth, the 1there are, however, many specific characters to which no adap- tive significance can yet be assigned.—eb. 4.8, evolution lamarck-darwin principle of ebranchement, of divergence, the adaptive radiation of osborn, which permeates the diversity of the plant and animal world. these five pioneer or zoologic principles, all alike discovered in zoology, have been confirmed and ratified in palaeontology as the principles of progression and of retrogression, mani- fested first only in the individual and finally in the race. they are the coefficients both of individual development and of racial evolution or phylogeny, as set forth in what osborn has termed “tetraplasy ” in ontogeny and “ tetrakinesis ”’ in phylogeny. to cite baldwin again:— coefficient. a. co-operating; acting in union to the same end. 2. that which unites in action with something else to produce a given effect; that which unites its action with the action of another. the two remaining principles are palaeontologic, namely (vt.) continuity and (vil.) rectigradation. to the zoologist every minute mechanical part of every animal is still and dead; to the palaeontologist every detail is alive and moving, slowly unfold- ing in the original sense of the latin evelvere (evolutio); to the vision of the embryologist, individual development is an unfold- ing of the potency of the germ. in this creative movement the palaeontologist discovers his two new principles, a sixth and a seventh, namely the principle of continuity, of continuous and unbroken advance or recession of each character from invisibility into visibility, and, closely connected therewith, the principle cf rectigradation, of the con- tinuous orthogenetic rise of each new organ out of heredity, pass- ing through stages of increasing mechanical perfection, then per- haps gradually subsiding again into the germplasm until it finally disappears. these seven principles which govern the origin of species in mechanical adaptation also concern an enlarged heredity, for only through palaecontology can we broaden and clarify our vision of heredity and distinguish the ripples of “‘ saltation ”’ or “f mu- tation’ (de vries) from the waves of “ evolution,” the local currents and vortices of ‘‘ variation ” from the rise and fall of the tide of great characters (cf. scott, 1894). the minute fos- silised tissues of the ivory tusks of the mastodon and the stu- pendous “ thunder-saurian ”’ brontosaurus are alike mirrors and ‘“‘ phenotypes ”’ of the evolving germ-plasm out of which they once developed. the stages in the evolution of the horse, camel, mastodon and elephant, in the largest and in the minutest detail, are mirrors of the evolution of the germ-plasm. palaeontology against vitalism or ‘f entelechy”’ the principles of rectigradation, that is, of the direct adap- tive origin of new specific characters from the germ, presents the greatest theoretic difficulties; certain new specific characters arise adaptively, without antecedent use or function, and are therefore unexplainable on the original lamarckian principles (lamarck, spencer, cope). nor is the cause of these ortho- genetic characters traceable to an “ entelechy ” or internal per- fecting principle, or to an evolution creatrice in bergson’s sense. new organs chiefly appear as secular reactions to new conditions of hfe. entirely inexplicable as the reaction process is, all of the numerous rectigradations which have been closely observed in many lines of descent are responses to secular changes in environ- ment or in habit. in this secular sense the lamarckian prin- ciple of new needs of the organism inducing a change of function and the change of function inducing change of structure acquires a new significance. for example, the browsing horse ( h ypo/ip- pus), remaining in a forested environment, retains an arrested dental mechanism, whereas the plains-living horse { hipparion), finally contending with the grasses of an extremely arid environ- ment, shows the most highly progressive and intricate dental structure; the browsing pleistocene proboscidean (afastodon) retains the same kind of grinder as its oligocene ancestor (palae- omastodon); the grazing mammoth (£. primtigenius) rapidly evolves a grass-eating mechanism. such facts as these, however, do not justify a revival of la- marckian confidence, because, taking biomechanical evolution as a whole as revealed in palaeolontogy, it is like a two-edged | to75 sword, equally damaging to the original darwin and the original lamarck hypotheses. it substitutes a firm and undeviating order in biomechanical adaptation, of which we have at present no conceivable explanation as to causes.! brp_tograpuy.—h. i’. osborn, the origin and evolution of life (1917-25); the origin of species as revealed by vertebrate palaeen- tology (1925); the origin of species ii. (1925) and the origin of species, 1859-1925 (1925), the definitions of “ principle ” and “ coefficient ’ are taken from baldwin's dictionary of philosophy and psychology: that of “ create” from the century dictionary. (eh. f. qo.) iv. theory of organic evolution two important advances in the study of evolution have taken place since 1859, when darwin published his origin of species. the first of these was mendel’s discovery of the fundamental laws of heredity, announced in 1865 but lost sight of until 1go00. the second advance was the discovery of the importance of dis- continuous germinal variation, whose value in relation to evolu- tion was foreshadowed by w. bateson’s work on afaterials for the study of variation (1894), and brought prominently forward by il. de vries in his afutation theory (1901). even before dar- win’s time it was known that new types, departing widely from the parent type, occasionally appear and that their characters may be inherited. the more extreme variations of this kind had been called sports. it was not realised, however, that many of the minute differences in individuals arise in the same way. the writings of august weismann between 1885-93, more especially his essays on the continuity of the germ-plasm as the foundation of a theory of heredity (1885), the significance of sexual reproduction in the theory of natural selection (1886) and the germ plasm (1889) had shown that variations originate in changes that first take place in the germinal material. his discussion of the problem of variation gave a new trend to all later studies on variability. twenty-four years later the pene- trating analysis of w. johannsen (1909), based on experimentally obtained data, furnished a secure basis for all later discussion relating to selection. these advances have furnished material for a scientific discussion of the evolution theory. the phyloge- netic generalities formerly indulged in when questions of varia- tion and heredity were discussed have to-day little more than his- torical interest; for it has become apparent that those discussions were lacking in a precise knowledge of the facts with which they dealt. a more detailed and systematic statement concerning those matters referred to above may now be made. mendelian turleory of heredity mendel (see mendelism, 18.115) has shown that when two plants belonging to races with contrasted characters, such as peas with green seeds and peas with vellow seeds, are crossed the hybrid offspring may be like one of the parents with respect to the pair of characters involved in the cross. if the hybrids are next bred to each other (or when monoccious, self-fertilised) the next gencration consists of the two kinds of individuals in the ratio of 3:1. mendel explained this ratio by assuming that one of the original races carried an element for yellow seed, the other race an element for green. when these elements are brought together in the hybrid the influence of one dominates the influ- ence of the other. if, at the time when the egg-cells and the pol- len grains of the hybrid reach maturity, the elements separate so that half of the germ-cells come to contain the element for yellow and half the other element for green, then chance fertili- sition of any egg by any pollen grain will give a three to one ratio. for when yellow meets yellow a pure yellow individual will re- sult; when vellow meets green a yellow individual will be produced (yellow dominating); similarly when green mects yellow a yellow individual will result; and when green meets green a pure green individual will be formed. the outcome is three yellow to one 1[t is important to recall that the study of palaeontology cannot in the nature of things give information as to the kind of hereditary processes occurring in evolution. the important fact of gradual evolutionary change established by palaeontology could be quite well accounted for by the accumulation by selection of small mutations.—epb. #.b 1076 green. of these three kinds one is pure for yellow and breeds true to that character; one is pure for green and breecls true to green; while two are hybrids, and, if selfed, will give again three yellow to one green. mendel also discovered that when two pairs of contrasted characters enter a cross, ¢.g., when a tall plant with coloured flowers is crossed to a short plant with white flowers, each pair behaves as above, and independently of the other, giving in conse- quence in the second generation four kinds of individuals in the ratio of 9:3:3:1. two of these kinds are like the two original grandparents; the other two present new recombinations of their characters. the same independent assortment of pairs of characters is supposed to hold for any number of pairs, but later results have shown that this is true only to a certain point. thus the inheritance of characters can be explained by the theory that there are independent elements in the germinal ma- terials (eggs and sperm-cells) to which, in a sense (see below), the differentials that distinguish individuals may be referred. equally important is the demonstration that these elements do not fuse or blend when brought together in the hybrid, but sep- arate there cleanly from each other, and half of the gametes come to contain one member of a pair and half the other member. when mendel wrote, no mechanism was known to which an appeal could be made to account for this separation (technically called segregation) of the elements in the hybrid, but, later, the extensive work carried out on the ripening of the germ-cells made it evident that the chromosomes furnish a mechanism that ful- fils all the requirements of mendel’s principles both for one pair and for more than one pair of elements. in the examples that mendel chose to illustrate the fundamental laws of heredity, one character completely dominates the other; but, while this often happens, in many other cases the hybrid character is more or less intermediate between those of the parents. thus when a white-flowered four o’clock is crossed to a red-flowered plant, the flowers of the hybrid are pink. nevertheless, the results inthe next generation (namely, 1 red; 2 pink; 1 white) show that the hereditary elements have not blended in the hybrid but separate as cleanly as do the clements for yellow and green peas. it is true that when a given character in one race differs from the con- trasted character of the other race in many elements (as height, e.g., tall ». short in man) the results are not simple but even here there is every reason to suppose that mendel’s laws also hold for the character pairs taken separately. each individual contains in every cell of its body as well as in the germ-cells two elements of each kind, one of which has come from the father, the other from the mother. in other words, it is not a characteristic of the hybrid alone to have pairs of cle- ments, but all ordinary animals and plants also are “ double ” or duplex. when the germ-cells mature the members of all these piirs separate and each ripe cell comes to contain half of the entire number. at the time of fertilisation of the egg by the sperm the full number of elements is again restored. the postulated elements in the germ-cells, now usually called genes, are not to be confused with the characters of the individ- uals for which, in a sense, they are responsible. each character is not supposed to be the direct product of one particular gene. on the contrary, characters or organs, as realised, are complex in origin—the product of a great many genes—but a difference that distinguishes one kind of individual from another may be due to a difference in only one pair of genes that act, so to speak, as differentials. moreover, there is much evidence to show that these differentials cause not only a single main difference but a great many other minor differences in all parts of the body. what is called a mendelian “ character” therefore 1s only the most conspicuous amongst these several effects, al] of which, however, accompany one or the other differentiating gene. whenever dominance is complete the measure of a given char- acter in the hybrid cannot serve as a measure either of the past history of the individual or of its potential progeny. tor exam- ple, if a grey house mouse is bred to a tame white or albino mouse the hybrid is grey and ts undistinguishable in colour from the house mouse, whose ancestry may never have contained a while mouse evolution and whose offspring by other house mice would be always grey; while half of the gametes of the grey hybrid that has had one white parent will contain an element for white. failure to recognise these simple facts made all the earlier work on heredity extreme- ly difficult and inaccurate when applied to individual cases. in this respect mendel’s discovery has made possible a more accu- rate interpretation of heredity, and consequently hasanimportant bearing on theories of evolution. since the elements in the gametes of the hybrid come out as they went in, the character of the individual is shown not to have any influence whatsoever on the elements in the germ-cells. it follows that lamarck’s theory of the inheritance of acquired characters is erroneous. that theory postulates that the char- acter of the individual has a direct effect on the germ-cells, so that the offspring show the influence of the characters of the body of the parents. if this were true there could be no reap- pearance of clean-cut elements in the gametes of a hybrid as mendel’s law postulates and as the facts demonstrate. since this law has been shown to hold, wherever tested, it follows that there is no influence of the sort postulated by lamarck’s hypoth- esis, although evidence is at hand to show that external agencies may, in rare cases, alter the gene, the altcration being then in- herited in mendelian fashion. applications of mendelism it thus follows that a theory of organic evolution must be in conformity with mendel’s principles, quite irrespective of the way in which the elements in the germ-material may be supposed to have arisen. there may be some dispute as to whether this or that character shown by domesticated animals and plants has arisen in the same way as have the contrasted characters in the wild forms from which they have been derived, but there can be no doubt that the elements or genes in both are inherited in pre- cisely the same way. mutation t heory.—the mutation theory, as it is called to-day, postulates that new types arise by sudden changes in the con- stitution of the germinal material. the new type, if sufficiently equipped to survive, shows the same degree of stability as the original type, 7.e., it breeds true to its new characteristics. the mutation may involve one striking change or many changes of small or large degree. whether the new mutant type is or is not to be called a new species is in part a question of definition, for it is true that new mutant types do not show for the most part, when bred to the parent stock, a peculiarity that has often been found to distinguish wild species when crossed, namely cross- infertility or sterility of the hybrids when such are produced. if this distinction is held as essential to the definition of new species, then it must be positively stated that most mutant types differing from the original type do not show this relation to the original type or to each other. there is, nevertheless, something further to be said before admitting this argument as the crucial test of the origin of tvpes by mutation or by any other process. the doctrine of the origin of new types by mutation owes its vogue to-day mainly to the work of hugo de vries, and to a large extent to his observations on an escaped variety of evening prim- rose (oenothera lamarckiana). he found that this plant pro- duces in each generation a small percentage of new types that breed true to their kind. these new types he called elementary species. they cross freely with the parent and with each other. it has been objected many times, especially by the opponents of the mutation theory, that the appearance of the new types in this evening primrose is due to its hybrid origin, and in support of their contention they point out that o. lamarckiana is not known to exist as a wild species. these who relied on thissevi- dence failed to appreciate that the appearance of its mutants does not conform to the ordinary rules of hybrid splitting, and their arguments were rudely shaken by the fact that other wild species of oenothera behave in this respect in the same way as does lamarck’s evening primrose. more recent discoveries have shown, it 1s crue, that a few of the more striking mutants of this plant owe their origin to proc- esses some of which at least can scarcely be admitted as repre- evolution senting, in general, the way in which wild species arise. an example of this may be cited here: one mutant type, o. gigas, is due to a doubling of the number of chromosomes; sev- eral others to the addition of an extra chromosome to the chro- mosome group, and the latter process is one that can hardly be supposed to be a method by which new species arise. there re- main still a few other types whose appearance is not yet clear, but some of them at least can be accounted for on the assumption of what is known as balanced lethal factors. without attempt- ing to discuss this technical question it may be said that the appearance of this last kind of new type does not represent the original act of mutating but rather the liberation of genes from their lethal connection. these genes may have arisen earlier by what is now known as point mutation. if so, some of de vries’ results fall into line with the results of more recent work on mutation. this work has shown that new characters arise from time to time as a result of a single change (point mutation) of an element of a germ-cell. ‘the new element gives with the one from which it arose a contrasted pair of mendelian units (called allelomorphs). if the new type is crossed to the parent type, the new and the old elements segregate in the hybrid as a char- acteristic pair of mendelian differentials. the new mutant type breeds true to its kind as does the parent type. the only serious question that may arise is whether these mutant types furnish materials for evolution, or whether they represent no more than the materials from which many of our domesticated types of animals and plants have originated. there can be no doubt that a large number of domesticated types have arisen in this way, nevertheless it might still be true that the origin of such types has nothing in common with the process by which wild types and species originated. a further consideration of the situation may help to show which way probability lies. 1. some of the mutant types are charactertsed by the loss of characters or parts present in the old type. the albino, for example, has no pigment in the eye, hair or skin. but evolution may be at times in the direction of simplification as with the eyes of many cave-dwelling forms. 2. new mutant types are often abnormal or defective. because of their small chance of survival such new types cannot, of course, be supposed to contribute materials for evolution, unless the origin of variations has some mystical relation to their fitness—a supposition not uncommon in the latter part of the 19th century. but nothing in the theory of evolution requires that all new variations shall be in the direction of fitness. for the theory of evolution it is only necessary that some sorts of variations appear that have a chance for survival in the old or in a new environment, 3. some of the new mutant types are less resistant (weaker) or are less fertile than the original type from which they arose. these under natural conditions would die out. in fact, many observations go to show that animals and plants under natural conditions are kept up to their top level of strength and fertility by the constant elimination of the less viable variations, wild types have already been brought as near the upper-limits as their particular organisa- tion is capable of, and it is not to be expected, therefore, that any particular departures from this type will be an improvement. the situation would not be very different if a change could be “ purpose- ly’ brought about, for, as stated, the adjustment of most organisms to the varied conditions under which they live—an adjustment that has been reached after an immense interval of time—may be as nearly perfect as the materials of its organisation and the varying condition of its environment permit. in a new environment or in a new relation to its present surroundings the chance for a change in an adaptive direction may seem greater, the relation of domesti- cated types to human needs or fancy supplies such a novel situation; but human intelligence as an agent in evolution, while it may speed up the process or increase the chances of survival of a particular type, bears the same relation to variability which makes evolution possible as does any other environmental agency. if the preceding discussion appears to weaken rather than enhance the value of mutant types as material for evolution, this is equally true for any other kind of material, unless there were kinds in which the response of the organism to a possible need takes place. carefully controlled observations have dis- covered no adequate evidence of this latter sort of variation. the extravagant claims and speculations that have been ad- vanced in support of such views rest on confused thinking or unwarranted assumptions or false deductions from insufficient evidence. | 1077 more specifically in support of the mutational origin of new types the following facts carry considerable weight: (1) the dif- ferences that distinguish wild variations and even wild species have been shown in a number of cases to depend on genetic ele- ments that behave toward each as do mendelian elements. (2) genetic elements that modify common characters, making them a little more or a little less developed, are well known. thev conform in every way to the laws regulating larger changes. many of the individual differences that make organisms a little better or a little less well adapted depend on these modifying elements. any theory of evolution based on observed facts, and not on imaginary supposilions, must appeal to these genctic elements as material out of which to construct a theory of evolu- tion or descent through gradual modifications. as already stated, it does not follow that these modifying factors, which can gener- ally be found when looked for, have arisen by mutations even though they obey mendel’s laws, but until some other origin can be discovered it seems better to construct a working hypothesis on this assumption than on one that appeals to purely fictitious agencies. (3) darwin argued that since all degrees of infertility between types and all degrees of fertility of hybrids are known to exist, there is no need to suppose that these differences have had any origin than other kinds of differences. in fact, if evolu- tion has taken place, we might expect to find just such an incon- stant relation. later work supports darwin’s contention. the attempt to set up artificial distinctions between the frequently observed infertility between wild ‘“‘ species’? and the complete fertility of nearly all domesticated and mutant types does not appear to-day as a real difficulty in the path of the mutation theory of evolution. : modern experimental research has brought to light an impor- tant distinction in relation to those individual dilferences that are always found to be present in any group (variety or specics) of individuals. the individual differences, that are often called fluctuating variations, are due sometimes to environmental effects produced on the individual during its development. these are not transmitted to the offspring and can take, therefore, no part in evolution. other individuz] differences are genetic differ- ences due to elements or genes in the germinal materials. these differences are inherited according to mendel's laws and may take part in evolution. at the time when darwin wrote the origin of species (1859) these distinctions were not clearly under- stood, although, of course, it had been known long before that time that while some individual differences are transmitted others are not. darwin’s theory of natural selection was based on the occurrence of individual variations, which, under selection, fur- nish the materials by which progressive evolution takes place. it was, however, not then sufficiently realised that selection of individual differences, even of those that are inherited, can not bring about an advance in the direction of selection to an indefinite extent. the changes due to selection come abruptly to a standstill unless new mutation occurs. the explanation of this is well understood to-day, owing more especially to the thor- ough examination of the problem by a danish botanist, w. jo- hannsen. the first advance that takes place under selection is due to the sorting out of the genetic differences present that modify this or that organ in one or another direction. when selection has brought together those genetic clements that modify a particular character in the direction of selection, further ad- vance ceases. the selected type will still vary, it is true, due to the environmental influence acting on cach individual during its development; but, since these are not inherited, no further ad- vance in the selected group of individuals as a whole takes place. only by the appearance of a new mutation or of some other sort of change is any further progress possible. ‘the rather widespread popular fallacy that selection can go on changing a group as long as the proccss continues is now known to be erroneous. the sclective process does not furnish a new base from which further progress may be made, but acts only in so far as genctic differ- ences are already present and then comes to an end, or unless new differences arise by mutation. it is a creative process only in so far as it sorts out what is already given. on the other hand 1078 if mutations are constantly arising, selection will gwide the resultant evolution. darwin’s ideas concerning the nature of variation and the power of natural selection could not have been as precise as the ideas of the present time based on accurate experimental work, and there is nowhere to be found any statement in his writings to the effect that selection itself creates the possibility of further advance in the direction of selection. it could not have been as clear to him as tous that the power of selection to bring about a progressive change in a given material is extremely limited. nevertheless, he took for granted that new variations are con- stantly occurring, and in all directions. if this were strictly true, selection would cause progress indefinitely. we realise that ge- netic variability is by no means such a common event as dar- win supposed. on the contrary, all the evidence indicates that it is a rather remarkably rare event in proportion to the individ- ual environmental changes that are ever present. compensating for the rarity of new genetic variations is the fact that when they do appear they are constant and not necessarily lost by the swamping effects of intercrossing. thus what the theory of natural selection lost in one direction it gained in another, and the probability that evolution has taken place by the selection of chance variations is as great as at the time when darwin ad- vanced his theory of natural selection. bisliograpiy.—gregor mendel, ‘' versuche itiber pflanzenhy- briden, ’’ verhandl. d. natur-vereins in brunn, vol. 10 (1865); a. weismann, essays on heredity, 2 vol. (oxford, 1889); the germ- plasm (1893); w. bateson, materials for the study of variation (1894); w. johannsen, uber erblichkeit in populationen und in reinen linten (jena, 1903); a. weismann, the evolution theory (1904); 1. de vries, species and varieties; their origin by afutation (1905); r. h. lock, variation, ileredity and evolution (1910); h. de vries, the mutation theory (1910-1); a. d. darbishire, breeding and the mendelian discovery (1911); w. bateson, mendel’s principles of iteredity (1913); w. johannsen, elemente der exakten erblichketts- lehre, 2nd ed. (jena, 1913); hl. de vries, gruppenweise artbildung (1913); w. bateson, presidential address to brit. assn. meeting held in australia (1914); r. r. gates, the mutation factor in evolution (1915); t. hl. morgan, the physical basis of ileredity (philadelphia, 1919); r. c. punnett, amendelism, 5th ed. (1919); e. baur, einfithrung in die experimentelle vererbungslehre, 5th and 6th ed. (1922); t. hf. morgan, a. h. sturtevant, h. j. miiller and c. b. bridges, the mechanism of mendelian heredity, rev. ed. (1923); w. e. castle, genefics and eugenics (1924); t. h. morgan, hvolution and genetics, (princeton, 1925); e. b. wilson, the cell in development and heredity, 3rd. ed. (1925). (t. h. mm.) v. evolution and response to environmental change the word evolution, literally translated, means unfolding or unrolling, and in latin signified the opening up of the bud into the perfect flower or leaf-shoot. its meaning was extended later by metaphor to denote the growth of an institution or a people. in the 18th century it was introduced into biology to denote one particular theory of the development of the individ- ual. according to this theory all development was a mere un- folding or unrolling: the perfect individual complete in all its parts already existed in miniature in the germ; growth consisted in separating out and making evident what had been previously wrapped up together. history of the term.—the geologist, lyell, employed it to denote the moulding of the earth by natural forces. darwin, in 1859, did not employ the word evolution at all in his celebrated book on the origin of species. when herbert spencer, in his famous first principles, attempted to show that the same process which had con- densed nebulae into suns and planets had also produced life from life- less matter and modern animals and plants from the first simple living things, he gave to this hypothetical process the name “‘evolu- tion’; but his term ‘ evolution "' has come into general use to denote the darwinian theory that the inexhaustible variety of living plants and animals have arisen by descent from a few or, perhaps, only one stock of simple ancestors. nature of evidence.—now since evolution is ex hypothesi, a process which required for its accomplishment millions of years, direct evidence of its occurrence is of course unobtainable, and the indirect evidence in its favour may be grouped under three heads, viz.: (1) deductions from the comparison of allied species with each other, (2) deductions from the comparison of fossil species with one another and with living species, (3) deductions from the comparison of the hvolution stages which the individual of one species passes through during its growth from the egg to the adult condition, with the adult stages of other species. darwin relied mainly on the first category of evidence. he showed that those who contended for the fixity and independent creation of each species, nevertheless divided many species into jocal races which in their view had arisen through the modification of different portions of the mother species by exposure to different types of external conditions, but that in practice no sharp line could be drawn between such races and species which graded into each other. huxley, however, relied chiely on the second category of evidence, for at the time of his great fight for darwin, scrics of closely related fossils deposited in immediately succeeding beds had heen discovered, in aa te? to his mind there was exhibited a veritable record of evolutionary change, the fossils in the lower beds being the remains of the ancestors of the animals preserved in the younger and succeeding beds. the comparison of the embryonic stages in the life history of one animal with the adult stages of another was brought into prominence by haeckel, who interpreted the life history of the individual as a recapitulation of the history of the race: this inter- pretation is of course a great assumption: its validity has to be first established by arguments drawn from categorics i and 2; but once its general truth is admitted it furnishes a splendid means of un- ravelling the actual course which evolution has pursued. present position.—the present position of affairs may be sum- marised as follows: by arguments belonging to all three cate- gories mentioned above, the educated mass of mankind have been convinced that evolution has actually taken place; that as time has flowed on a species has gradually changed its character and that one mother species has split up into local races which, by diverging more and more from one another, have gradually changed into distinct daughter species. but how this has been brought about is an extremely disputed question, for the con- stancy of specific characters within the span of observation afforded by a human life is the most familiar of all the facts of natural history. main hypotheses —three main hypotheses as to how evolu- tionary change has been produced have been put forward, the lamarckian, the darwinian and de vriesian respectively. lamarck’s hypothesis in its original form was that the direct cause of evolution is a change in the environment. animals exposed to new conditions experience new needs, and the effort to satisfy these needs leads them to make greater use of certain organs and less use of others; greater use leads to greater growth and lesser use to diminished growth; and these tendencies to greater or less growth are transmitted by heredity to offspring. darwinian hypothesis —the darwinian view is that change of conditions induces a tendency in animals to vary slightly in all directions; that many of these variations are inheritable, and that those that happen to suit the new environment are preserved and affect the character of subsequent generations, whilst the individuals which exhibit harmful variations are wiped out by natural selection. darwin implicitly assumed that the descend- ants of each individual exhibiting a favourable variation might be expected to vary again in the same way as did their progenitor, and that so the character of the stock would be gradually modi- fied in a given favourable direction. mitation theovy.—the theory of de vries is founded on his experiments with the evening primrose oenothera lamarckiana. he found that when thousands of this plant were cultivated in the botanical gardens at amsterdam, in each gencration a small number of individuals were produced which exhibited marked divergences in structure from the type, divergences which at the same time affected roots, leaves, stem, flowers and seeds. in nearly every case the divergent individual, when fertilised with its own pollen, transmitted its peculiarities to its offspring; so that new species were being produced from the mother species in each generation complete in all their characters. the causes of this production of new species, however, were quite mysterious, and de vries suggested that species underwent fits of variation. to very similar conclusions morgan was led by his cultures of the fruit ly drosophila mclanogaster, of which he has bred several hundred thousand individuals. here, too, small numbers of individuals, differing definitely, though to varying extents from the type, were encountered, and each such individual, when mated with its like, transmitted its peculiarities to its offspring. morgan believed that in these aberrant individ- evolution uals he had discovered the raw material of evolution, and is usually known as the “‘ mutation theory.” pure lines.—the reason that the mutation theory has gained in favour whilst the pure darwinian theory is less widely ac- cepted than formerly is to be found in the results of what are called the pure-line experiments. galton and weldon had shown that if the individuals of species are measured with respect to the development of a single character, they did exhibit varia- tions on both sides of the mean of approximately the same extent and with very nearly equivalent frequency, but the question remained to be answered whether these variations were inherit- able or not. this question was attacked by johannsen, agar and jennings, each of whom investigated inheritance in a pure hne— that is, amongst the offspring of a single parent. johannsen chose the bean-plant, in which the flowers can be fertilised with their own pollen; agar worked on the little crustacean simoce- phalus, in which the eggs develop parthenogenetically, that is, without fertilisation; and jennings chose the protist paramecium, commonly known as the slipper animalcule, for his investigations. this animal is equivalent to a single cell and multiplies by divi- sion into two. in all three cases it was found that the progeny varied considerably amongst themselves, but that if a divergent individual were selected to carry on the strain, the progeny of such an individual were exactly like those of a typical individual and that the possibility imagined by darwin of continuously increasing or diminishing the size of an organ by continually selecting in each gencration for continued propagation those in- dividuals which exhibited the largest or smallest developments of an organ did not in fact exist. difficulties and criticisms of the mutation theory.—the ob- jections to the mutation theory are of a different character. while “‘ mutations ” do appear suddenly and are in most cases inheritable, most of the mutations described by morgan and the “sports ’’ used to propagate fancy races in other species, differ strongly in their character from the diagnostic marks which dis- tinguish allied species from one another. on this subject the judgment of leading systematic zoologists is decisive. most mu- tations are as haecker has recently expressed it: “‘ inhibitions of development ” and correlated with diminished vital energy. as they never fail to make their appearance when plants are cultivated or animals bred in confinement there must be what baur terms “ idiokinetic factors’ in environments of this kind which alter the hereditary tendencies. the nature of these fac- tors has been investigated by tornier in the case of goldfish. no domesticated race of animals exhibits such aberrant types as the goldfish; but all the divergences of structure from the normal are the secondary results of what tormier calls ‘ plasma-weak- ness”? or the diminished vital energy of the protoplasmic part of the egg, in consequence of which this portion became crushed and distorted by the swelling yolky portion. this weakness is due to the deprivation of the egg of sufficient oxygen during the critical period of its development immediately succeeding fertilisation; but once acquired, this weakness is transmitted from one generation to another and produces similar results in each. if tornier’s conclusions are accepted, ‘‘ mutants ” can have played no part in the process of evolution, for owing to their relatively feeble constitution they would be the first to be eliminated by natural selection. lamarckian hypothesis ——as to lamarck’s principle of “ re- sponse to the environment ” as the cause of evolution: that ani- mals do respond to changes in the environment by slight changes in habits and consequent modifications of structure is admitted by all, so far as the life of the individual is concerned. the point in dispute and one that is vital for the evolution theory is whether such modifications can be transmitted in any degree to subse- quent generations. thus, children who run about with bare legs acquire an abundant growth of hair on these members, profes- sional singers acquire enlarged chests and prize-fighters enor- mous muscles in their arms. it is obvious that if these changes affect the children of such people the changes in structure will keep pace with changes in habits, or, as it is usually phrased, structure will change with function. 1079 evolution of the horse—in the succession of fossil remains, which convinced huxley of the truth of evolution, this slow concomitant change of structure and function is the salient fact which impresses itself on the observer. thus, in the series which is apparently the record of the evolution of the horse, we start with animals with four toes on each foot. as we proceed upwards in the series the outer toe, corresponding to the human little toe, gradually diminishes in size and disappears first on the hind foot and then on the fore foot. the second and fourth toes then begin to diminish slowly and are ultimately reduced to mere vestiges concealed under the skin, in which condition they remain in the modern horse, leaving only the third toe active and functional. whilst the toes are shortening the teeth are undergoing changes also. in the earlier four-toed forms the grinding teeth are stud- ded with cusps—-but as we ascend in the series the cusps become connected by ridges, and the vallevs between the ridges become filled with cement and the crown is at the same time greatly in- creased in height. he changes both in teeth and feet are clearly related to the gradual changes of swampy plains into dry steppes, and the resultant modification of succulent soft marsh plants into dry harsh grasses. embryological evidence —but the study of comparative em- brvology leads also to the conclusion that evolution results from changes in habits. whenever in an order, where the type of structure is fairly constant, one genus is met with which exhibits an aberrant type of structure, this aberrant genus, when young, almost invariably exhibits the structure characteristic of the other members of the order. the cat-fish, widely distributed over europe and asia,(see distribution of animals) are fresh- water fish devoid of scales and with darkly pigmented skins. they have broad mouths adorned with long barbels, which have been fancifully compared to the whiskers of a cat. there is a cat-fish, however, which is a denizen of small ponds and tanks in india, belonging to the genus claritas, which has learned to breathe air. this fish, when young, is exactly like other cat-fish, but as it grows a sac-like extension of the opercular cavity is formed above the gills and into this cavity peculiar tree-like organs extend. ‘these organs are adapted to absorb oxygen from the air; they arise as little buds from the uppermost sections of the gill arches, and as they grow the fish begins to make excur- sions out of the tanks on to the swampy meadow and gardens round them in pursuit of earthworms. it is difficult to take seri- ously the suggestion that “ accidental”? mutations led to the production of the trees in fish which remained in the water and that then these aberrances enabled their happy possessors to extend their hunting grounds, whilst other simultaneous muta- tions inspired them with the instinct to do so. zoological evidence.—the study of closely allied species or de- tailed systematic zoology has led dr. tate regan, to exactly the same conclusion. change of habits, he avers, has preceded and determined change of structure and so caused evolution. so in the case of the viviparous blenny zoarces, which retains the young in the maternal body till they have acquired the struc- ture of the parent and are ready to assume the parental habits, small colonies of this fish in different localities differ from one another slightly in the shape of the body. those that live in the quict headwaters of the danish fjords have shorter and deeper bodies with a reduced number of vertebrae, while those that lead a more active life in the open sea have longer and more slender bodies with an increased number of vertebrae. activities— habits—are here, as lamarck phrased it, called forth by the de- mands of the situation in which the fish find themselves and be- come crystallised into changes of structure. transmission of acquired or adoptive charactcrs.—most palae- ontologists are supporters of the lamarckian view, but so far the evidence adduced in favour of the lamarckian view has been indirect; the question now arises: can we induce animals to adopt different habits from those to which they have been accustomed, and show that these changed habits and the modifications re- sulting therefrom are transmitted to- their descendants? weils- mann, who on theoretical grounds was strongly opposed to the theory of the inheritability of the effects of habit, endeavoured 1080 to give a negative answer to this question. tle cut off the tails of mice and bred these mutilated specimens together and showed that their progeny were born with normal tails. these experi- ments, which betray ignorance on the part of the experimenter of what the lamarckian doctrine was or what was meant by an “ acquired character,” have been cited for a generation as con- clusive evidence against this doctrine. recent experiments ——of recent years, however, a series of carefully planned experiments have been carried out which give positive answers to the question. thus, kammerer took speci- mens of the common european f'ire-salamander, (sulamandra maculosa) and reared them in cages the walls of which were coloured yellow or black. the skins of these animals are black diversified with patches of yellow pigment. this yellow pig- ment, however, only makes its appearance at the time of the metamorphosis of the gilled larva into the jand-living adult. it varies in extent in different individuals. during larval life kam- merer kept his specimens in surroundings of a neutral grev tint; after metamorphosis he placed relatively black specimens in yellow cages and yellower specimens in black cages. in these cages they lived and grew till they reached maturity, a process which occupied between four and five years. at the end of this time the specimens in the yellow cages had amalgamated their yellow spots into two broad longitudinal dorsal bands; in those in the black cages, on the contrary, the spots had dimin- ished to minute dots. when two yellowed specimens were mated together and their offspring reared to maturity in yellow boxes, the yellow increased so much in extent as almost to exclude the black pigment altogether: when on the contrary, these offspring were reared in black boxes the ycllow pigment still increased in guantity for the first year of their life owing to the influence of paren- tal conditions; then, and then only, did the black environment begin to exert its effect and the yellow pigment was ultimately reduced to small spots. durkhen enclosed the caterpillars of the common white butter- fly (pierisbrassicae) in boxes covered with lids of orange-coloured glass. in these boxes they pupated, and from the pupae the but- terflies emerged and were used to propagate a second generation. the orange-coloured light inhibits the formation of the pigments (chalky white and minute dots of black) in the skin of the pupa and allows the green blood to shine through. in ordinary light about 4% of the pupae are green: of those reared in orange light 65% were green. when a second generation were reared under similar conditions 95% were green, and when this generation was exposed to the influence of ordinary daylight 34° were still green owing to the influences to which their parents were exposed. macbride once endeavoured to force the stick insect (caraz- sinus morosus) to feed on leaves of the common ivy plant. the insects disliked this plant very much and took to it with reluc- tance—those that survived produced few eggs, but these eggs produced larvae which took to ivy with avidity when opportu- nity offered. time factor —lamarck had expressly asserted that the influ- ence of conditions in modifying structure only begins to be evi- dent “‘aftera long time,’ and all the evidence derivable from palae- ontclogy bears out this conclusion. pigmentation, however, is the most recently acquired and variable character which ani- mals possess; and it was therefore to be expected that it would be this character which would yield results to experiments conduct- ed over a relatively limited period of time. the objection some- times raised that the changes induced in these experiments might not be permanent is due to a confusion of thought. the objector tacitly assumes that a change in hereditary tendency, once pro- duced, should persist, whatever the nature of the subsequent environment may be. but if hereditary potences are of such a nature that they can be deflected from their course by environmental change, a transference of the organism back to typical conditions must work in the opposed sense to the previous environmental change. the utmost that we could expect in such cases would be (1) an intensification of the effect when the environmental change is lvolution prolonged for several generations; (2) a trace of the effect, es- pecially in earlier stages of life, when the organism in the second generation is removed to normal surroundings; these expecta- tions are fulfilled by the results of kammerer and durkhen. it appears therefore that the whole constitution of an animal can be expressed as a superposed series of adaptations or habits. this, indeed, has always been the basal assumption underlying comparative anatomy—and that these habits have produced corresponding structural modifications. those most recently ac- quired are assumed to be most quickly affected by changes in conditions—long established habits acquire a kind of inertia, or are, so to say, more “‘ deeply engrained ” and only yield slowly to new stimuli. two a priert theoretical objections have been made to the ilamarckian doctrine by its opponents. these are: (1) that there are structures, such as the peculiar features of neuter insects and the phenomena of mimicry im insects, which could not have been evolved by the handing on to posterity of the results of changes of habits, and (2) that there is no conceivable mechanism by which changes in the body of the adult organism could be transmitted to the egg-cell. the first objection may be at once countered by the reflection that in many cases where the evolutionary history has been clearly deciphered the dependence of change of structure or change of habit is obvious. if in these difficult cases alluded to above we knew the evolutionary history, the same explanation would be seen to apply to them. elsewhere (see bibliography ) suggestions have been made as to how these exceptional cases might be explained, but it is waste of time to discuss them until we know more of their history. the mechanism.—to the second objection we may reply that whether we can conceive it or not some means of transmitting the effects of changes in bodily structure to the egg must exist. guyer and smith made an emulsion of the lens of the eye of a rabbit in ringer’s solution and injected it into the blood of a fowl. after an interval of three weeks the scrum of the fowl’s blood had acquired the power of attacking and dissolving the lens of the rabbit’s eye. if now this serum were injected into the veins of a pregnant rabbit some of the embryos were born with minute defective lenses. if these young were allowed to breed the defect could be transmitted through six generations without any further administration of serum, and was, moreover, trans- mitted through the male, so that any explanation of the trans- mission by a supposititious infection of the embryos of each gen- eration through the placenta of the mother was excluded. guyer was driven to the conclusion that the germ-cells of the rabbits originally injected had acquired the power of forming a ‘‘ cytol- ysm ” which destroyed the lens, and that this power was trans- mitted by heredity. but it is really idle to raise the objection that there is no “ mechanism ” by which the properties of the body can be trans- mitted to the egg. no “ mechanism ” is yet discovered by which the growth of the adult body from the egg can be explained. evolution of planis——does evolution as a result of the trans- mission of the effects of habit apply to plants also? as there is a strong fundamental similarity in the characters and reactions of living substance in both animals and plants, it is to be expected that plants, like animals, will inherit acquired qualities. but the life of the plant and all its reactions are much slower than those of an animal, and the period of a human life would probably be too short to demonstrate this inheritance. some evidence, how- ever, exists. in the 17th century the peach tree was introduced by the french. colonists into the island of reurion. in france the peach is a deciduous tree, but those planted at sea-level in reunion became evergrecns, whilst those on the summits of the mountains remained deciduous. if now the seed of a tree living at sea-level is planted at a higher elevation, it remains an ever- green, so that this acquired habit has become hereditary. to sum up, there 1s in every organism something which feels, reacts by striving, learns, remembers and iransmits its memories to its posterity. striving and memory are fundamental proper- ties of life and give the only satisfactory explanation of evolution. evolution bratiograpny,.—g. ih, t. eimer, die fintstehung der arten (1888- 1901); e. d. cope, the primary factors of organic evolution (1896); g. b. lamarck, zoological philosophy, trans. h. elliot (1914); p. kammerer, the inheritance of acquired characteristics (1924); e. w. macbride, introduction to the study of heredity (1924); and article a zoology,’ "in evolution in the light of modern k nowledge (1925); eugenio rignano, biological memory: a new theory of life, english translation and introduction by e. w. macbride (1926). (e. w. macb.) vi. evolution and mind the word “ evolution ” has been used in many senses. some of them may now be regarded as obsolete. but there is still diversity of usage. traced to its source this is not mercly a mat- ter of verbal definition. it depends on the place that is assigned to mind in, or in relation to, the course of events. in what may be called an unrestricted usage of the word “ evolution,” mind is the outcome of the progressive differentiation and integration of world-events. in a specially restricted usage those world- events which are distinctive of organisms are the outcome of the directive activity of mind. this divergence of usage is based on the acceptance of this or that speculative hypothesis. on one hypothesis mind is the evolutionary ferminus ad guem: on the other hypothesis mind is the creative terminus a quo. but the biologist within his province may reject both these hypotheses. for him evolution is neither more nor less than a doctrine of descent. take first the unrestricted use of the word. the noun stands for a concept of very wide range, and needs adjectival qualification or referential completion to focus its meaning. thus we read of cosmic evolution, of mental evolution, of social evolution; of the evolution of the atom, of the solar system, of scenery and so forth. those who accept this unrestricted usage must be prepared to state that which is common to each several instances of the use of the noun, when they talk, for example, now of geological and now of mental evolution, or turn from the evolution of a crystal to that of trial by jury. herbert spencer, who rendered current the unrestricted use of the word, enunciated a “ law of evolution ” stating certain criteria which he regarded as salient. but his formulation is rarely quoted now save by those who seek to show the inadequacy of the concept he sought to express with such emphasis on redistribution of matter and motion as seemed to leave mental and social evolution interpretable only on a basis of questionable analogy. those who still use the word in an unrestricted sense mean by it something comprehensible though necessarily expressible only in very comprehensive form. they mean something like this: any set of events or state of affairs, physical or mental, which exemplifies evolution is a passing phase in an orderly sequence; and it comes into existence in such wise that its place in the se- quence, and its relations to precedent and consequent phases, are interpretable under the accredited methods of scientific pro- cedure. otherwise stated: evolution implies a determinate plan of advance to which any given instance of advance may be re- ferred, and as thus referred is susceptible of interpretation, such interpretation is commonly spoken of as natural. but it is com- monly held that there are some phases of events or some states of affairs of which no natural interpretation, evolutionary or other, can be given. these are said to be supernatural. if we wish to understand why so many people regard evolu- tion as a live issue we cannot disregard this antithesis between natural and supernatural. but though it is preserved in much controversial discussion, nay more, is widely regarded as essen- tial, it has for long been subjected to criticism. many urge, rightly or wrongly, that it is a relic of primitive mythology. there are those who believe that some world-events demand supernatural intervention in order that the direction they take may be explained, whereas other world-events do not. hence one must ask: which do and which do not? but many eminent thinkers believe that the concept of supernatural intervention, here, there or elsewhere, as directive of the current course of world-events, should be ruled out as invalid. the supernatural, they urge, is omnipresent. if they be right, the antithesis be- tween “ some ” events and “ others ” lapses. the question then losi is: are all world-events not only natural but in some valid sense supernatural also? we are not here concerned with this philo- sophical question. but we must not prejudge the issue. hence we must be content to say: there are at any rate some events which occur in enchained sequence of which it may be affirmed that to all these events the concept of evolution in an unrestricted sense is applicable. a further question then arises. does every enchained sequence of natural events furnish an instance of evolutionary advance? of course there is temporal sequence; and this may be called “ advance in time.”’? but this means only that in any sequence of phases, sav 7, #2, 2, 2 precedes #2, which is succeeded by w. it tells nothing of the character of the group of events /, m orn. if there be evolution some change of character is implied. now it was one of herbert spencer’s noteworthy contributions to the discussion of enchained natural sequence that he sought to dis- tinguish groups of events or states of affairs as in some sense “lower”? and “higher.” progress is from lower to higher; regress is from higher to lower. evolution is always progressive. regressive change is not evolution but ‘ dissolution.” the difficulty still remains how to characterise in some way “ higher ” and ‘ lower.” it may be that at present we can best deal with the question departmentally and say that 2 1s higher (or lower) than m, as an organism, as a mind, as a social institu- tion and soon. but to justify the concept of unrestricted evolu- tion there must be some character or characters, which may be taken as distinctive of all instances of what we are to call “ high- er.” perhaps there is as yet no common agreement as to the criteria on which reliance can be placed. it has, however, been suggested that complexity in the constituents of any ?, m or m, and comprehensiveness in their plan of going together as an integral whole may serve to distinguish higher from lower in any context of natural events. so far we have taken the sequence of events, say /, m, 2, as susceptible of observation or infcrable from observation duly recorded. let us assume that /, # and #, are integral entities whercin certain natural events as constituents go together in sub- stantial unity in accordance with some determinate plan, as in an atom, a molecule, a crystal, an organism. then m may be (1) a stage in progressive evolution, or it may be (2) a stage in regressive ° ‘dissolution.’ let »: be an atom of lead. it is admit- tedly in being. we seem to have evidence of its becoming or natural origin, in isotope form, by regressive dissolution of the uranium or the thorium atom. but we have as yet no evidence of its origin through progressive evolution. if, however, mm be a molecule, say of water, there may be evidence of its origin (1) in this instance by evolution or (2) in that instance by dissolu- tion. and if # be an organism its status in being may have been reached either by evolutionary progress from an organism which was lower than it is, or by regressive dissolution (degradation) from one which was higher than it is. here we take it for granted that 7, m and # are affiliated organisms. it may then be said that, since there is no affiliation in atoms or molecules or crystals, the words evolution or “ dissolution ” (in the biological sense of regressive degradation) are inapplicable. furthermore, in liology, adaptation means changing attunement to changing external conditions and of such progressive or regressive adapta- tion there is no evidence in the inorganic world. we thus pass from the unrestricted usage to one that is re- stricted to that province of inquiry in which /, m or # are living organisms. and here yet a further restriction is customary— namely, to that which is otherwise spoken of as the ‘ doctrine of descent,”’ where /, #2 and 2 are aftiliated organisms, reserving the word ‘ development ” for the branch of inquiry which deals with 7, # and # as stages in the life-history of the individual. the question then arises: in what way is the story of the individ- ual development (ontogeny) connected with the story of racial or linear evolution (phylogeny)? now it is part of the business of the biologist to describe (1) the intrinsic nature of this or that organism, and (2) its extrinsic relations to the world in which it lives—its environment. in order that it may continue in being (survive) there must be 1082 adaptation to surrounding circumstances. the evidence of such adaptation must primarily be sought in the story of development in the course of individual life. but the story of /, of sm and of 2, as affiliated individuals, may have much in common in respect of their intrinsic nature and of their adaptation to environing con- ditions. in any evolutionary hypothesis, that which is common to the affiliated organisms /, # and 7, is discussed under heredity (see heredity). apart from a doctrine of heredity there can be no doctrine of descent. and this applies to the intrinsic na- ture of the individuals, and to the adaptation of these individu- als to their environment. such in brief—apart from contributory matters—is the con- cept of evolution in a restricted sense. it neecls emphasis, how- ever, that under intrinsic nature and adaptation there are com- monly included such mental characters as may be attributed to the organism on presumptive evidence. this provides for mental evolution on a doctrine of descent. we may now ask on what grounds one usage or the other is accepted. they may broadly be distinguished as practical and speculative. there seems to be a hierarchy of modes of being. and this hierarchy may be reducible to the three modes of being, physico-chemical, vital and mental. the unrestricted theory is that these three exemplify the evolutionary sequence /, m and x and are interpretable as successive stages of world-progress in one order of nature. the vital m has certain distinctive char- acters, such as hereditary adaptation, which are absent in /; the mental 2 has characters which are absent in #—let us say en- deavour to reach a foreseen end. the presence of » implies that the stage m has already been reached; the presence of # implies that the stage 7 has already been reached. it does not neces- sarily follow that m can be interpreted in terms of /, or that 2 can be interpreted in terms of m. nay rather it seems, on the evidence, that in passing from / to m, and from m to x, there is something really new. for this the word ‘‘ emergent ” has been suggested. emergence labels the concept which may thus be expressed: when certain constituents with distinctive character- ising properties go together in accordance with some determinate plan so as to form an integral whole, the properties of that whole are not the algebraical sum of the properties of the constituents as they exist (a) independently or (b) within some other and different whole. there are #ew properties which are said to be emergent. whether there be in nature instances of emergence in this sense is a matter of evidence. if so they may be found only in /—in the physico-chemical realm, or they may be found also in m and in x. wherever they be found, we must loyally accept this find- ing, which implies that in these cases—not necessarily in all cases —evolutionary advance is by emergent steps with continuity of direction towards higher modes of being. acceptance of some such evolutionary scheme for the interpretation of life and mind is admittedly on speculative grounds. on practical grounds botanists and zoologists of the older school may say: we keep to known facts and work within our province. of an enchained series of steps from the not-living to the living there is at present no evidence which carries conviction. we start, therefore, with organisms in being. we adduce evidence in favour of evolution, by which we mean a doctrine of descent. we adduce evidence from which we infer that, accompanying certain organic events, the physiological nature of which we seek to characterise, there is in some organisms, but not in all, and even in man in some but not all of his behaviour, conscious guid- ance which contributes to fuller life and to nicer and more deli- cate adaptation. this “ mind” we accept where the evidence justilies its acceptance, just as we “ accept ”’ life on the evidence. we find it in being at a describable stage of individual develop- ment. it is then a factor in further development and on this wise, under heredity, a factor in organic evolution. it is not with- in our province to ask: whence does life arise? or whence does mind arise? when once they are in being (through what mode of becoming, sudden or gradual, is unknown) we trace their evolution under our doctrine of descent. we submit that all this is based on sound scientific method. evolution i.et us grant that it is based on sound biological method, and that the botanist or zoologist is wise to keep within his own province. but there are border-land sub-provinces in which other specialists are busily at work, and the interconnection of provinces (physico-chemical, organic and mental) is itself worthy of serious discussion. we must set no barriers to scientific inquiry. unrestricted evolution 1s unquestionably speculative in the sense that it is a hypothesis to be accepted or rejected on eviden- tial grounds. it includes in i1s purview the origin of living beings and the origin of conscious endeavour to attain foreseen ends. under restricted evolution biologists of the older school exclude these questions of origin (that of life and of mind) either (1) as beyond the scope of their special inquiry, or (2) as one with which science has no concern. but in either case they commonly urge that conscious endeavour as distinctive of mind, comes into elfective existence quite late in the developmental history of the individual and quite late in evolution under their doctrine of descent. and when it does come, so as to be a new factor in adaptation to environing circumstances, they commonly accept as an unexplained fact that it in some way “ accompanies ”’ cer- tain highly differentiated physiological events the story of which falls within their province. there is, however, a newer school of biologists, and among them the logically consistent extremists say: not late in the course of development or of evolution does mind appear, but at the very outset of life, which from first to last is but the organic expression of mind as endeavour to accomplish its ends in development and evolution. for them evolution assumes a radically different meaning. it is still restricted to the realm or order of life and mind as definitely contrasted with the utterly diverse order of matter and energy. here only is endeavour in being, but here always. even in the plant, even in the fertilised ovum, even in processes of cell-division, that endeavour which is distinctive of mind, and which is absent in the inorganic realm, intervenes as directive of the course of events. the word ‘ supernatural ” may not be used, but sufficient emphasis can be laid on the analogous concept—“ wholly other than naturalistic or deter- ministic.”’ endeavour belongs to a disparate order of being, that of the mind which animates the organism and uses the material provided by nature as a means to the accomplishment of its ends. however stereotyped the development of oak from acorn may be, it is none the less the expression of life which is one with mind and is utterly different from the forces concerned in any mechanical occurrence. it betokens a persistent and consistent aim directed to, and directive of the fulfilment of ‘ oakly ” being. it is this that is spoken of as endeavour; this that demands a concept which is inapplicable to atoms or molecules or crystals or the solar system. such a form of restricted evolution is a speculative hy- pothesis to be accepted or rejected on evidential grounds. what is the evidence in support of the cardinal concept? that is the crucial question which must here be left sab gudice. in view of the rival claims of this special form of restricted evolution on the one hand, and of unrestricted evolution on the other hand, controversy, often embittered, arises, and there is talk of ‘ obsession ” by this or that “ dogma.’”’ the issue is at the bottom the place and the status of mind in its relation to matter. dr. broad has recently discussed no less than seventeen logi- cally possible solutions of this vexed problem under certain definitions. they lie beyond our purview here. much has been written—much remains to be written—on evolution. the care- {ul reader should ask: which of at least three different usages of the word is implied in this or that statement, in this context or that? birliography.—fvolution in the light of modern knowledge, a collective work (1925); as presenting the restricted view j. arthur thomson, concerning evolution (1925); for unrestricted treatment, c. lloyd morgan, life, mind and spirit (1925); for a critical discus- sion of underlying principles, without special reference to evolution, but with much emphasis on emergence, c. d. broad, the mind and its place in nature (1925). (c. li. m.) examinations examinations (sce 10.41; also intelligence, human}.— as far as great britain is concerned progress since 1911 has been made in three directions:— (1) it is suggested that the following criteria applicable to physical tests should be applied as far as possible to exami- nation tests: (a) the test of a given characteristic should demonstrably yieldl a suitable measure of that characteristic; (b) in cases where the whole material under investigation cannot be tested, it should be shown that the sample tested is an average sample of the whole; (c) the test should be trustworthy, 7.e., when repeated a number of times by the same observer, or when repeated by different observers, it should yield approximately the same results; (¢) the application of the test should not sensibly affect the characteristic tested, or injuriously affect the material as a whole; (ce) the characteristic tested should be demonstrably of a permanent or semi-permanent nature.! (2) the british govt. has taken action with a view to the improvement of the most difficult civil service examinations in the country and of secondary school examinations. the report of the treasury committee on civil service, class i. examina- tions (1917), has led to important reforms in that examination, of which the chief are the introduction of a viva-voce examination and the modification of the examination in ‘‘ english ” so as to make it a real “‘ capacity-test ”’ of “ the understanding of english and the workmanlike use of words.”’ ‘the test in this subject has now a definite purpose and is designed to meet that purpose; and the whole tendency of the examinations in other subjects is also to test capacity rather than mere memory. the secondary schools examination council set up by the board of education in 1917 is making, with the help of expert investigators in each subject, periodical investigations of exam- inations and scripts with a view to correlating the standards of public examinations at the ages of 16 and 18 (approximately), conducted by universities and other public bodies, while avoid- ing the introduction of an educational dead-level which would block progress. this “ continuous audit ” of examinations is valuable, and probably the first of its kind. in regard to one point there has been no visible advance—the statistical investi- gation of the marking by different examiners, in which edge- worth’s important researches remain almost isolated. starch and elliott, in 1913, showed that the marks allotted independently to a single script by 115 mathematical teachers varied from 28 to g2, confirming edgeworth’s results.2, further investiga- tion of this point is essential. in regard to “ interview ” and viva-voce examinations, there appears to be far greater uniform- ity of valuation.’ (3) the development of intclligence tests has introduced a new element into examinations. in the marking (or ‘ scoring ”’) of these tests, differences between different examiners are elim1- nated: the tests are “‘ trustworthy ” as defined under (1) above. ballard (joc. cit.) points out that most ordinary examinations are incidentally tests of english composition, which is difficult to mark; whereas in “ intelligence ”’ tests writing is reduced to a minimum, the answer being often given by a mark or a number instead of by words. but much of the old difficulty remains as to the precise significance of the cxamination results in their bearing on the purpose of the examination. the fact remains that in the emergency of the war the “ group-tests,” which are rapid, were successfully applied in 1917-8 in the united states of america to nearly 2,000,oco men with the object of separating them into various classes for military employment or registering them as unemployable (see jon anatrysts).* ballard, who has extended the new methods to such school subjects as history and geography, claims that there is a high degree of correlation between the results and the estimates of teachers based on long 1p. j. hartog, examinations and their relation to culture and efficiency (1918). 2see p. b. ballard, the new examiner, p. 182 (1924). 3 cf. sir stanley leathes on ‘' the qualifications . . . of pub- lic servants,” jour. of public administration, 1, p. 356 (1923). 4c.s. yoakum and r. m. yerkes, amfenial tests tn ithe american army (1920). 1083 experience. the consultative committee of the english board of education in their important report on psychological tests of educable capacity, etc. (1924), state that ‘ though in the present state of development of ‘ intelligence’ tests it is hardly possible to explain simply what is measured or tested by them, it is tolerably well established that these tests ... have shown themselves capable of giving a useful common measure- ment of what teachers generally call capacity or intelligence.” the committee think the new tests will probably exert an im- portant influence on examinations of the ordinary type, and recommend especially that further research should be instituted into the use of individual “ intelligence ” tests in connection with oral examinations for all ages or types. although progress has been made, there is still much room for the improvement of examinations, it being especially necessary to define the exact purpose of each examination, and to ascertain by investigation how far it fulfils that purpose. brbliograpily.—in addition to sources quoted, circular 906 of may 25 1917, of the board of education, london, re the secondary schools examination council; publications of that council; chap- ters on “ examinations "’ in the calcutta university commttssion re- port, vol. 2, chap. 18; vol. 5, chap. 40; vol. 7, app. 18 or if (p. j. h. the united states examinations in subject matter in school and college have been undergoing a very radical change during the period 1910~26. this chanze may be characterized as a turning away from the old- type question, which asked the candidate to “ describe,” “ state” or “ explain ”’ in essay form a certain topic, to the new-type ques- tion, which calls for a specific response to an item, this response being made by underlining, checking or writing a word or at most a phrase. in an old-type examination ® the candidate might be asked to write an essay in answer to the question, ‘‘ describe the secretion of gastric juice.’ in the new-type examination his knowledge about gastric juice would be tested by his responses to many short items. such items may take several forms, as will be hlustrated by items from different subjects:— analogy: gastric juice is to the stomach as (saliva, adrenin, fears, bile) is to the lachrymal glands. completion: the part of a circle included between two—and an —is called a sector. recognition: planets move around the sun in orbits that ere circular, el/fptical, hyperbolic, cylindrical. true-false: t. f. the chief crop in ohio is tobacco. there are many different varietics and combinations of such forms, and those quoted above must be considered only as sam- ples. the reasons for this change from old- to new-type examinations may be ascribed to the unreliability of the old-type and the devel- opment of the new-type item in intelligence testing. the old- type question is difficult to score accurately and it fails to cover the whole field of the subject examined. the development of group intelligence tests led the way to a study of the technique of constructing the questions, arranging them in sub-tests and in standardising the whole test. the methods of scoring were also developed through the group intelligence test. the construction of an examination in a school subject for nation-wide use (general- ly called a standardised educational test) is now quite a techni- cal matter. there are such standardised subject-matter exami- nations or tests for practically every subject taught in the ele- mentary and high schools of the country. in addition to these standardised tests made by experts, teach- ers are everywhere using the new-type examinations in their class room work. wood? describes such examinations at the university level and russell ® shows in detail how school teachers can con- struct such examinations in a)] subjects in the elementary school. he goes further and suggests how they may be used as effective teaching devices. none of these authorities advises the absolute 5examples taken from d. g. paterson, preparation and use of new-t ype examinations. yonkers, 1925. 6w. a. mccall, tow ta measure in education (new york, 1922). 7b. d. wood, measurement in higher education (yonkers, 1923). 8c. russell, classroom tests (boston, 1926). 1084. abandonment of the old-type essay examination, but all of them believe it to be insuflicient for the accurate examination of the pupil. all of them emphasise the necessity for a careful construc- tion of the new-type examination, and they maintain that it can be made to measure the pupil’s ability to reason. they deny that it merely tests the memory of the pupil. these new type examinations are now being used by such ex- amining bodies as the college entrance examination board and the board of examiners of the new york city board of educa- tion, and by many civil service commissions, both state and mu- nicipal. in public personnel studies, a journal issued by the bu- reau of public personnel administration, institute for govern- ment research at washington, suggested examinations for a great many civil service positions have been published. almost all of these examinations are of the new type. (r. pr.) excess profits duty.—this describes a tax on the excess of the actual profit of an accounting period overastandardof profit. i. in the united kingdom immediately after the outbreak of war in rgr4 it was appar- ent, from the movement of the monthly index numbers of the wholesale prices of commodities, that profits of businesses, espe- cially of those concerns whose products would immediately be in increased demand, would move upwards at a rate even greater than that shown by the index number. for instance, the sauerbeck-statist index number for july 1914 was 82-4, by dec. it was 91:6 and in july rors it had reached 106-4, or an increase of over 25% in 12 months. when the results shown by accounts of trading concerns embracing part of the war period became available to the authorities, the figures which emerged more than confirmed this anticipation, and so the excess profits duty was born. it was imposed by part 3 of the finance (no. 2) act 1915, which passed into law on dec. 23 of that year. scope of the duty.—the excess profits duty was a duty, where a chargeable amount of profit existed, on the profit of trades and businesses carried on in the united kingdom, or owned or car- ried on in any other place by persons ordinarily resident in the united kingdom. the duty did not extend to the profit derived from husbandry in the united kingdom, or from the exercise of a profession or from offices or employments—though in certain cases the remuneration of directors and other persons concerned in the management of a business was indirectly made subject to the duty. the duty was imposed upon the profit of a business concern as an entity, and not by reference to the profit or income of individuals as such. a chargeable amount of profit was the excess of the actual profit of an accounting period over a standard of profit increased by certain free allowances. an accounting period was in general the period for which the accounts of the business are made up; it might cover any period not exceeding 12 months. both for the accounting period and for purposes of the stand- ard, profit was determined, subject to the modifications sect out in the statutes, on the same principles which determined profits under the income tax acts. it was limited to the profit inuring to the proprietors of the business, exclusive (with certain excep- tions) of interest received on investments. interest paid upon loans and other charges upon the business was therefore declucted in arriving at profit. — standard of profit.—the standard of profit was represented in the normal case of a business which had been carried on for some years prior to the outbreak of war by either: (a) 4 profits standard, or (6) a percentage standard. a profits standard was normally the average profit of any two of the three years to the end of the last accounting period ended before the outbreak of war. in exceptional cases the profit of a different period of pre- war trading was adopted. a percentage standard was nor- mally a statutory percentage (in the case of companies 6% and in other cases 7% for accounting periods ended on or before dec. 31 1916, and 8% thereafter) on the amount of capital employed in the business at the end of the last accounting period ended before the outbreak of war. provision was mace for the increase of these percentages in the case of classes of excess profits duty trade or business which proved that the capital employed in the class of trade or business was subject to special circumstances (e.g., special risk, etc.). applications for any such increase of the statutory percentage was dealt with by a board of referees appointed for the purpose by the treasury. a large number of such applications was made to that board, embracing many trading activities carried on abroad by british concerns, c.g., mining, teaplanting, etc., and numerous awards were issued by the board increasing the statutory percentage. since the scheme of the duty involved a comparison of the profit of the accounting period with the standard of profit (the excess of the former over the standard being the amount on which the duty was charged), it was necessary that the basis of computation should be similar and comparable in both cases. provision was therefore made for a reduction or increase of the profit of the accounting period, by reference to a statutory per- centage upon the additional or reduced amount of capital employed in the accounting period as compared with the capital employed during the period or at the date to which the standard related. the statutory percentage here referred to was for cases where there was a decrease in the amount of capital employed, 6°% in the case of companies and 7% in the case of other persons since the imposition of the duty. where there had been an in- crease in the amount of capital the statutory percentage was at. different times: in the case of companies, 6, 9 and 11%; in the case of other persons, 7, 11 and 13%. capital as computed for the purpose of the duty represented the proprictors’ trading capital, and borrowed money was, therefore, excluded from the computation of capital. in general, capital of a business consisted of money; assets acquired by pur- chase at the price paid, subject to any deductions for wear and tear or replacement; debts due to the business and assets not acquired by purchase taken at their value when they became assets of the business. accumulated profits employed in the business were treated as capital; any capital (the income of which was not taken into account in computing profits for the purposes of duty) and any borrowed moncy or debts were to be deducted in computing the capital. assets paid for otherwise than in cash were to be taken at the value of the consideration when the asset was acquired, but if the business had been con- verted into a company so that the shares therein were held by the late owner, no value was to be attached to those shares so far as they were represented by good-will or otherwise than by material assets. for this purpose patents and secret processes were deemed material assets. the free allowance was in general £200 for an accounting period of a year. in certain cases of ex- soldier, etc., proprietors of businesses it was {500. relief under the original act-—special provisions affording relief from the full weight of the duty were introduced as from jan. 1 1917 in the case of small businesses. the relief was given either by reference to the deficiency of the profit of the accounting period below a prescribed sum (at first a sum of £2,000 for an accounting period of a year and subsequently £4,000), or by ref- erence (as from jan. 1 1920) to a substituted standard depend- ent upon the number of working proprietors and the capital employed during the period or at the date to which the original standard related. a special and novel feature of the duty was found in a provision under which in the normal case a percentage—equal to the percent- age rate of duty in force for the period concerned —of any deficiency of profit of a business below the standard in any accounting period was set off against the amount of duty applicable to an excess of profit over the standard in another period. special provisions were included in the statutes as regards busi- nesses where there had been only two pre-war years or only one or part of one pre-war year, or where the business had been commenced since the outbreak of the war; as regards depreciation and obsoles- cence of assets, unremunerative capital, remuneration of directors, etc.; the businesses of local authorities, industrial and provident so- cictics and of shipping; and other matters of detail. in the case of an accounting period which commenced before and ended after any of the times stated, the excess profits were appor- tioned on a time basis between the relative parts of the accounting period and the apportioned parts of the profits were charged at the several appropriate rates of duty. excess profits duty the duties imposed are shown in the following table:— rates of duty on the amount by which the profits from any trade or business to which the law applied, in any accounting period which ended after aug. 4 1914, exceeded by more than {200 the pre-war standard of profits excess profits arising:— o (a) within a year from the commencement of the first accounting period! . ; : : : , 160) (0) after the end of the period mentioned in (a) but before jan. rrgt7'. ; ; : ‘ : : : . 60 (c) during the calendar years 1917 and 1918 ; . . 80 (2) during the calendar year 1919 ; ; ; . . jo (e) on and after jan. 1 1920, until parliament otherwise determined e # swe as 2 ie. «60 ‘in the case of trades or businesses commencing after aug. 4 1914, the rate was 50%, if the accounting period ended on or before aug. 4 1915, and 60 % if it ended thereafter. munitions levy.—for a time there existed side by side with the excess profits duty another duty known as munitions levy, or munitions exchequer payments, which was imposed by the muni- tions of war act 1915. [t applied only to certain concerns or parts of concerns engaged in the manufacture of munitions or war mate- rials which the minister of munitions ‘ controlled ’’ under the pro- visions of that act. the act limited the profits of controlled establishments, as from the date of control, to a retainable amount, ascertained in accord- ance with the statute and rules made thereunder. any excess of net profits of the establishment over such retainable amount was pay- able to the exchequer in the form of munitions levy. pe retainable amount of profits was, broadly speaking, made up of :— (2) the standard amount of profits, (6) one-fifth of that standard, (c) special allowances for increased output or for increased capital, and (d) special allowances for exceptional services by the controlled owner or other exceptional circumstances. controlled establishments liable to the munitions levy were liable also, like other trades and businesses, to the general excess-profits duty, but under section 48 of the finance act 1916, it was provided in effect that the concern should be liable to pay for any period an amount equivalent to the higher of the two charges, but not both. the operation of the munitions levy was terminated as from dec. 31 1916 by the finance act 1917 (section 24). the ground for the repeal of the levy as from dec. 31 1916, is to be found in the fact that as from that date the rate of excess-profits duty was increased to 80%. at that rate the duty became, practically without excep- tion, the heavier charge, and the munitions levy would, if it had been continued, have been inopcrative in its result. | repeal of the duty—'xcess-profits duty was abolished by the finance act 1921. as different businesses had become first subject to the duty at different dates, provision was made for them to cease to be liable to the duty at different dates in such a manner as to result in every business which had commenced before the outbreak of war being subject to the duty for an aggregate period of seven years and no longer. businesses which had commenced after the out- break of war had their liability terminated at a fixed date of dec. 31 1920, refund of relief.—lt was a general principle that against the duty chargeable upon the excess profits of any accounting period there might be set off the duty applicable to any deficiency of profits sus- tained in another accounting period. the various changes which were enacted in the rate of duty made it possible for a taxpayer to be required to pay an amount of duty in excess of his aggregate net excess profits over the whole period for which the duty was in force. to obviate this anomalous result, provision was made that in such cases the excess should be remitted or repaid. in calculating the duty to be compared with the net aggregate excess profits, payments of munitions levy were to be counted as payments of excess-profits duty to the extent that duty would have been payable if muni- tions levy had not existed. part of the productivity of the duty was due to the continuous rise of the price level, and as carly as 1917 the trading community, anticipating that at some time this period of high prices might be succeeded by a heavy fall in prices, urged upon the government the necessity of providing relicf from excess-profits duty, in any cases in which losses were incurred shortly after the duty came to an end, in consequence of such a fall in value. complex provisions to this end were contained in the finance act 1921, granting three reliefs in connection with trading stocks, two of which were alternative to one another. a maximum period of four years from aug. 31 1921, within which relief could operate, was allowed. during the four years from 1921 to i924, inclusive, £184,000,000 of excess-profits duty and munitions levy were repaid, and a large part of this repayment is to be ascribed to these reliefs. that the fears of the trading community as respects the price level were justified, is shown by the movement of the sauerbeck-statist index number from its peak of 266-1 for april 1920 to 134°8 in april 1922, 1085 the net amount of duty collected and retained in the exchequer from the inception of the tax to march 31 1926 was {1,280,000,000. even at that date a considerable volume of arrears was still out- standing, although the authorities anticipated that little more benefit to the exchequer could be expected. in order to expedite the clearing up of arrears, steps were taken in 1922 to charge simple interest at the rate of 44% per annum with- out deduction for income tax on excess-profits duty outstanding as from the date at which the debt became payable, or, if it had become payable on or before jan. 1 1922, as from that date. in the earlier years of the debt the number of assessments made was about 50,000, but when prices were at their peak the number of concerns liable to the duty was round about 70,000. yield.—the approximate true excess profits arising in accounting oe classified in financial years were officially estimated to be as ollows:— approximate true excess accounting periods ended profits in the period or year aug. § 1914 to march 31 1915 . . 50,000,000 year to march 31 1916 ; . 200,000,000 year to march 31 1917 . 350,000,000 year to march 31 1918 . 430,000,000 year to march 31 1919 . 500,000,000 year to march 31 1920 . 600,000,000! year to march 31 1921 . 200,000,000! 1 subject to revision in the light of assessments still being made for accounting periods ended in the year 1919-20, and 1920-1. the estimate for the latter year does not allow for the reduction in value of trading stocks arising after the end of the final accounting period under the relief provisions. qv. fe*c,) il, the united states although during the american civil war the state of georgia had adopted (1863) a tax on business profits in excess of 8% on the capital stock, at rates varying from 5% to 25% according to the amount of such excess profits, the first federal excess- profits tax was adopted in the act of march 3 10917, for the purpose of creating a ‘‘ special preparedness fund.” after the united states entered the world war, this tax, at higher rates and in more complex form, was continued in the acts of oct. 3 1917, feb. 24 1919 and nov. 23 1921. in all these acts, less use was made of pre-war profits as a base than in the british. acts. the american tax was aimed at “supernormal profits ” —profits in excess of normal profits—rather than profits in ex- cess of pre-war profits. the decision to subordinate pre-war profits was made deliberately by the framers of the law on the ground that a deduction based upon invested capital was simpler, better designed to serve as the basis of a permanent tax, and more equitable in that it prevented tax-payers from escaping the tax merely because they had been unusu- ally prosperous before the world war. under the american tax a business which had been unusually profitable before the war and merely maintained the former rate of profits during the war, was still subject to a heavy excess-profits tax. how- ever, minor recognition of the war-profits idea was incorporated in the act of oct. 3 1917; and for the one year 1918 a dual or alternative tax was imposed, the taxpayer in effect paying an 80% war-profits tax or an excess-profits tax at progressive rates of 30% and 65%, whichever tax was larger. during the years 1919-21 only the excess profits tax was retained. provistons.—the 1917 law applied to all trades and businesses, including professions and occupations, but beginning with 1918 the tax was confined to corporations, excluding ‘‘ personal-service corporations.’ the normal exemption or ‘ excess-profits credit ”’ consisted of a specific exemption of $3,000 plus 8% of the invested capital. income in excess of this credit but not in excess of 20° of the invested capital was taxed (after the year 1918) at the rate of 20°, and the remaining income, if any, at the rate of 40%. the upper rate for the year 1917 rose to 60° and for i918 to 65%. under the act of oct. 3 1917 the specific exemption to individuals and partnerships was $6,000; but to corporations only, $3,000. yield —judged by the standard of productivity—the most im- portant quality of a war tax—the excess-profits tax was conspicuously successful during the world war. the yield of the tax was as shown on following page. the figures for 1918 represent possibly the largest annual amount ever produced in one country by a single tax. during the years 1917-9 the excess-profits tax produced more than 25% of the total ordinary receipts, but despite the high rates, the tax was collected 1086 without crippling industry, owing to the high level of profits and to the protective effect of the normal exemption, the relief provisions, and the large degree of administrative discretion authorised in the law. excess-profits tax returned for calendar year 1917 = individuals, etc. s$1o1,249,781 partnerships 103,887,984 corporations . i ,633,747,740 total $1,843,885,505 1918 2,505,565,939 i9ig 1,.431,805,690 1920. 988,726,351 i92t. 335,131,511 in accordance with the promises of both political parties, the tax was repealed, after stubborn opposition, as on dec. 31 1921. the termination of the tax gave rise to no special problems such as arose in great britain, because under the american tax the liability of the taxpayer for any one year was not dependent in any important way upon his income for other years. the repeal of the tax was due mainly to the sharp decline in its productivity under peace conditions; its discrimination in favour of overcapitalised concerns and against conservatively financed corporations; the general belief that it was passed on, loaded with additions, to the general body of consumers; its capricious inequalities; and its great complexity. the com- plexity of the tax, which, in the words of one secretary of the treas- ury, threatened to cause an administrative breakdown, is illustrated by the fact that the tax liability for the year 1917 of many of the large corporate consolidations had not been finally determined at the close of the year 1925. bibliography.—r,. h. montgomery, excess profits tax proce- dure (1920); r. m. haig, taxation of excess profits tn great britain, american economic review, vol. x., no. 4 suppl. (1920); treasury department, regulations 45 (1920); commerce clearing house war tax service (1921); g. fe. ifolmes, federal income taxes (1923); prentice-hall, federal tax service (annually). cl sa)