SOME of the most remarkable peculiarities of our theoreticians of race, who call themselves “anthropo-sociologists”, is the fact that they leave us all the more in the dark as to the true nature of the concept of race, the more they have occasion to manipulate with this concept in the explanation of social phenomena. A man’s being, action, performance, are due in their opinion simply to his race; they have been inherited from his ancestors and are transmitted with the certainty of natural law to his descendants. Race is the modern Fate, as inscrutable and immutable as the latter.
It seems self-evident to the anthropo-sociological theoreticians of race that those groups designated as human races should be understood in the same way as we understand races of animals. They seem to be not troubled for a moment by any question as to whether the life conditions of man do not alter the concept of race as applied to man. They do not even take up the question of which type of animal race is represented by the human races.
As a matter of fact, the races of animals are not all of the same type, but may be divided into two different groups: the races of domestic animals, and the races of animals in the wild state.
Zoologists and botanists distinguish these groups with great care. As a rule, they apply the word “race” only to the former, while the latter are termed “varieties” or “species”. The theoreticians of race, the anthropo-sociologists, however, indiscriminately apply observations and laws valid for both the races of domestic animals as well as for the varieties of wild animals, to the human races. This alone must give rise to dreadful confusion, altogether aside from the fact that human beings are neither domestic animals nor animals in the wild condition, but a tribe living under quite peculiar conditions, conditions which do not resemble those of any other animals.
Before taking up the problem of race, we must therefore first attain clarity as to the distinction between the “race” of the domestic animal and the “variety” of the wild animal. We speak here only of animals, since only they are of importance to our problem, which concerns the human races, but the following remarks apply just as well to plants as to animals.
A phenomenon is best understood when its origin is known. In the case of the races of domestic animals, it is not difficult to ascertain this origin, for the process is being accomplished daily before our eyes. The breeding of new races is constantly going on. On the other hand, the formation of varieties in nature cannot be observed; it must be inferred as an hypothesis.
If we regard the organisms in nature, we shall find that none of them serves a purpose lying outside of itself, but that each is an end in itself. Its individual organs must serve for the preservation of the whole, and must therefore be adequate for – or at least compatible with – self-preservation. An organism constituted otherwise cannot continue to exist, and certainly not to multiply.
But in the case of the animal organism, not only its own organs are important, but also those of other organisms with which it comes in contact, which oppose it, or on which it lives. Only man, however, has advanced to the point of altering in such manner the organs of the organisms from which or by which he lives, as to make them more subservient to his purposes. This is one of the means by which he has advanced beyond his primitive condition.
His first step in this process is to cause animals (also plants) which he would otherwise be obliged to seek out and capture with more or less difficulty, to live and multiply in his proximity. His first object in this is probably merely to diminish the difficulties of seeking, perhaps also of overcoming, the organisms on which he lives. But once the latter have been accustomed to live together with man as tame companions, man is also impelled to attempt to adapt the organs of the domestic animal, or of the cultivated plant, to his own purposes, for which nature did not intend them.
This is best attained by adequately altering their conditions of life, by increasing their supply of food, perhaps by fertilizing or battening, decreasing their expenditure of strength in the life process, for instance, by sparing them the necessity of looking for fodder, of fleeing from enemies, of losing heat in the winter cold, etc. But, ultimately, man comes to the point of altering these organisms by making use of his observation that each individual has the tendency to transmit his qualities to his posterity. Much as all the individuals of the same species may resemble each other, they are never completely identical. Slight variations are always present, and these may easily be transmitted.
Most domestic animals finally become so amenable to man’s guidance that he is enabled to mate them, or prevent them from reproducing, as he likes. Once he has advanced to this point, he will, of course, prefer to permit those specimens to reproduce that are most suitable for his purposes, that furnish most milk, meat, or fat, or yield the finest wool, or lay most eggs, have most traction power or swiftness, etc. If those of their posterity continue to reproduce, who present these qualities in the most emphatic form, these qualities will gradually be reinforced to such an extent, and the bodies of the animals will alter so greatly, as to be perceptibly different from those of their ancestors, thus producing a new species from the old species, with permanent, repeatedly transmittable characteristics, provided the breeding-animals are always mated only with their like.
This selection is at first predominantly an unconscious one. The best specimens are reproduced because they are most prized. Without any intention of securing a new race, this final outcome of the process has not been apparent from the outset. But the art of breeding is perfected more and more, becomes more and mare conscious, and finally actually sets out to create specific races with specific race traits. At times, new variations may sporadically appear in isolated specimens. If these are of advantage to man, he will attempt to reproduce them. Thus, in 1791, a ram with short, crooked legs and a long back, which was thus prevented from jumping over hedges, gave rise to a new race in America, that of the Ancona sheep. Likewise in France in 1828, a hornless ram with uncommonly soft, long wool, led to the creation of a new race, the Mauchamp sheep. As a rule, however, the creation of a new race is not such a simple matter, but proceeds by means of a slow, gradual reinforcement of traits, often discernible in the first generation only to the trained eye of experienced breeders, and not attaining practical significance until they have been reinforced to a sufficient extent in the course of generations.
The uninterrupted selection of breeding-animals, continued for generations according to the same plan, creates a new race which is maintained by the fact that only such specimens are reproduced as present this race trait in the most emphatic form, that a mating with individuals of other races is strictly avoided, and all specimens of the specific race which present a variation that deviates from the desired race trait are of course excluded from further breeding.
The necessary condition for the formation of such new races is, of course, that the animals reproduce in the tame state and that their mating be under man’s control. The elephant, as a rule, reproduces only in the wild state and has created no new races.
On the other hand, the domestic cat leaves nothing to be desired in the way of prolificness, yet the cat has preserved much of its original freedom in spite of man. Its love-life is carried on not in the stable but on the roofs, and therefore, according to Darwin, it does not furnish any different races within the same country. 
However, the formation of new races under otherwise identical circumstances will be the easier, the greater the certainty to mate specific individuals, and the more swiftly the generations succeed each other. This is the reason for the great increase of races of rabbits and pigeons; here the breeding of such races has become a sport.
Let us now examine the case of the formation of varieties of animals in the wild condition, which should – it would appear – have been examined before we took up the races of domestic animals, for the wild varieties, of course, arose earlier and constitute the fundamental trunk from which the races of domestic animals have branched off. But in a study of the history of the theory of the evolution of races, the origin of the organisms controlled by man is the proper point of departure, for it was the observations made in artificial selection that led Darwin to construct his hypothesis of natural selection.
Darwin assumed that the formation of varieties and species proceeds in the natural condition, as in the case of domestic animals and cultivated plants, by a selection of the best, most adapted, specimens for reproduction, and excluding from reproduction those less fitted, with the sole difference that the selection, in the natural condition, is not conducted by man, in accordance with his purposes, but by the struggle for existence, which is a consequence of overpopulation, of the circumstance that more individuals of each species are produced than can continue to exist. A constant merciless struggle is going on among them, in which the weakest, least fit, succumb, while the strongest, most fit, maintain themselves and reproduce. Serious objections were raised to this view at the very outset. If the struggle for existence is a continuous, progressive selection of the best specimens, the transformation of species must be going on continuously, and at a rather rapid rate. In the case of certain domestic animals and garden plants a specific new race may be produced in the course of a few years.
In nature, on the other hand, observation shows us that species remain apparently unchanged for long periods. They may change in geological periods, but remain unchanged for many thousands of years within a geological period. In historical times, the great mass of wild animal species has remained entirely the same. As depicted on the ancient Egyptian and Assyrian monuments, they look exactly like their prototypes of today. We are told this difficulty may be eliminated by assuming that evolution proceeds with tremendous slowness, by a gradual accumulation of imperceptible alterations. But the slower this evolution, the more imperceptible the alterations contributed to progress by each generation, the more insurmountable becomes another difficulty in the theory of selection: it becomes more and more impossible to assume that each alteration bestows upon the individual producing it a preponderance over other individuals not supplied with it. In artificial selection, the selection is made by men who already have in mind the new type that is to be bred, grasping its practical advantages and appreciating – through eyes that have been sharpened by this prophecy – the significance of hardly perceptible alterations, which are important not in themselves, but merely as points of departure in a long chain of development, the new type being realised only at its termination. The theory of evolution attempts to dispense altogether with providence in the formation of natural species. Without the aid of far-sighted selection, however, imperceptible alterations cannot become the cause for the survival and reproduction of the individuals supplied with them. Reference to artificial selection is here of no value at all.
In addition, we have a third difficulty: Darwin called his theory of natural selection an explanation of the origin of species. If correct, this theory would merely afford an explanation of the evolution of more highly organised individuals from those less. highly organised. Its whole emphasis is laid on the solution of the problem of evolution. But, in order to explain the origin of species, we must also explain the similarity between individuals, which leads to generalising them as a specific species. Whence this similarity?
In the case of artificial selection, the cause of the similarity between individuals is in their common descent from the same ancestors. The ancestral tree is here of great importance. But it is impossible, in this case, to maintain a “pure race” without constant intervention on the part of the breeder, who must carefully guard his race animals against mating with others, and who must eliminate from their posterity all those individuals that present alterations deviating from the pure racial type.
In nature this breeder is lacking. Unless the alterations are of such variety as to doom the individual to early destruction, they will not prevent it from mating with other differently constituted individuals, and thus from reproducing. A constant mingling of individuals with the most varied changes will take place.
A breeder producing anew race, furthermore, is concerned only with a specific one-sided peculiarity, which he aims to perpetuate. His selection is made solely with this object in view. But in nature, it is not merely a single quality which affords advantage to the individuals possessing it; the most varied qualities may be of value. Let us assume the theory of selection to be correct to the extent that evolution takes place by reason of the fact that individuals with advantageous alterations maintain and reproduce themselves more easily than others. Even here, the most varied alterations are possible, as we may see from the case of the hare. Some hares will be benefited by longer legs, others by greater endurance, a third variety by better protective mimicry (perhaps they are white in winter and brown in summer), a fourth group by reason of enhanced productiveness, others again through increased power of resistance to climatic influences (perhaps they have a thick pelt in winter, a light one in summer) ; finer differences in the sense organs, sharper eyes, better hearing, finer sense of smell, as well as differences in intelligence, in swiftness and correctness of the judgments based on sensual impressions, will be of advantage. One individual may present one set of advantages, another may have other advantages.
If only such individuals should continue to mate as have coincident traits, they might emphasise these traits and thus create a new race. But since there are many such traits, a single species within the same region would not give rise to a single new species but to many such. Thus, as contrasted with wild rabbits, tame rabbits may be divided into many races.
But a mating limited to individuals of the same peculiarities is impossible in the wild state. The character of the mates there depends entirely on accident, on the mating of certain individuals at the moment of the mating season. There is not always sexual selection; mating is often promiscuous. Where there is such selection, it is limited to one sex. The victorious stag will have relations with all the does of his herd, regardless of their properties. And the selection – if present at all – is carried out among a small number only.
In the wild state, therefore, the most varied deviations will be transmitted within a certain species. These deviations continue to mingle again. It is impossible to see how natural selection can here produce new important species with coincident traits. If a constant progressive evolution takes place owing to the survival of the fittest, with new properties and by means of their transmission, this evolution must lead to a disintegration of existing species into a confused mass of varying individuals, all similarity among which will progressively disappear. The theory of the origin of species becomes a theory of their dissolution, and it remains impossible to grasp how species based on the similarity of numerous individuals should ever arise. But, as a matter of fact, we find in nature many more individuals having coincident traits than we do among domestic animals. We have already pointed out how great is the number of races of tame rabbits, as compared with the uniformity found among wild rabbits and field hares.
And the number of species of wild animals is not increasing, while almost each new year supplies us with a new race in the case of many domestic animals
“But geology shows us, that from an early part of the tertiary period the number of species of shells, and that from the middle part of this same period the number of mammals, has not greatly or at all increased.” 
In the introduction to his fine book on the distribution of the animal world, Kobelt says: “I have not been able to convince myself that a sole, uniform transformation of the animal kingdom is taking place over long periods, as a strict interpretation of Darwinism would require ... Beginning with the middle Pliocene period (the geological period immediately preceding the origin of man – K.), we cannot prove with any degree of certainty the new origin of any species.” 
Whence then the great similarity between so many individuals in the wild state?
We cannot explain this similarity by considering only the individual and the evolution of the individual. We are here dealing with a mass phenomenon, which may be explained only by means of a factor lying outside of the individuals, above them, influencing them all in the same manner. It is not hard to discover this factor if we consider the varieties of animals in the natural state. Among races of domestic animals, the individual ancestors, the ancestral tree, is of importance. But the varieties of wild animals are “geographical races”. This is true even for the domestic cat, which resists artificial breeding; it is all the more true of animals in the unrestrained, natural state.
Thus, among lions, we may distinguish the varieties of the Barbary lion, the Senegal lion, the Cape lion, the Persian lion, the Guzerat lion. Among elephants, we distinguish between the Indian and the African. Rhinoceroses are divided into several varieties: the Indian rhinoceros, “whose area of distribution seems limited to the Indian peninsula”; the Varana rhinoceros, “as far as our knowledge goes, is found only in Java”. “The half-armored rhinoceros is found only in Sumatra (Cerator hinus sumatrensis).” “The area of distribution of the double-horned rhinoceros (Atelodus bicornis and Atelodus simus) now extends over all of Central Africa.” “The hornless rhinoceros is said now to be limited to the southern half of Africa.” 
Similarly in the case of the hare: “All of central Europe and a small portion of western Asia is the home of the Continental hare. In the south, it is the Mediterranean hare, a deviating species of small size and reddish color; in the high mountains, it is the Alpine hare, in the far north, the snow hare ... The African hares differ from ours by their smaller size and also by their uncommonly long ears.” 
In other words, it is the geographical differences which produce the differences between varieties in the natural state: differences in climate, configuration of the soil, the nature of the nutrition and the mode of obtaining it, the species of enemies, etc. On the other hand, it is the uniformity of the conditions of life within a certain region which produces the similarity between the individuals of the species concerned. This similarity is more powerful than the differences, the variations of the individuals. The latter tend to be dissimilar, to diverge. The conditions of life in nature, in a certain region, are the same, however, for all, operate in the same way, and oppose the tendency.
If we thus consider the conditions of life, the milieu, as the decisive factor in the moulding of varieties and species in the natural state, we are eliminating the difficulties that would arise if we should proceed – in our explanation of natural varieties – from the experiences obtained in the breeding of the races of domestic animals.
We are now enabled to understand not only the similarity of the individuals of the same species within a certain region, but also the constancy, the tendency to immutability, of species in historical times, as well as their alterations in geological periods. As long as the milieu remains the same, the species will not change. But the milieu doe not permanently remain the same. The earth changes, alters its position in the firmament. Passing through space, together with the entire solar system, it may at times encounter colder regions, at other times warmer ones, in what we call the universe. Nor is its position always the same with regard to the sun; its axis oscillates, and many portions of the earth’s surface may thus obtain a more polar climate than formerly, while others obtain a more equatorial climate.
Far more certain than these changes are those arising from the gradually growing coldness of the earth, its gradual shrinking. Continents and oceans are formed, some of the latter deep, others shallow; flat lands and mountains, marine currents and trade winds, nothing permanent, everything changing, but changing only in endless periods. For thousands of years the same condition will prevail in a certain region; then it will gradually change; moisture yields to drought, warmth to cold, low plains are lifted up, twisted into mountain chains, or subside and furnish sea bottoms. When such changes ensue, the organisms of the region cannot remain the same. Some are destroyed, some are driven out, forced to migrate, some adapt themselves to the new conditions, which they may do in many ways, for which Lamarck and Darwin, as well as their disciples, have gathered very interesting illustrations. But once the organisms of the region are adapted to the new condition of affairs, we no longer find any cause for further changes of their condition, and they will remain in their new forms until new changes in their life conditions are introduced.
This is not a new view. Darwin himself, in the historical sketch introducing his book on the origin of species, points out that Isidore Geoffroy Saint-Hilaire had stated it to be his opinion (in 1550) of the traits of species, “that they are permanent for each species so long as it reproduces itself within the same conditions, but that they change when the external conditions of life change”.
Darwin fully recognised the effect of the altered conditions of life as well as of the use or non-use of organs. But he underestimated their importance, since he was completely dominated by the observations made in artificial selection, and by the assumption of a constant struggle for existence under the pressure of over-population. This latter view he owed to Malthus; it is still considered a cast-iron law of natural science.
But if we examine the struggle for existence, we shall find that overpopulation-in other words, the struggle between individuals of the same species for fodder-plays but a small role, is only an exceptional phenomenon.
A few concrete examples will help us. Hares, as is well known, are very fruitful. The female hare gives birth to a number of young as early as the month of March; very few of these survive; how many, depends chiefly on the weather. Snow, freezing weather, will destroy almost all of them. Sunshine, warm breezes, will enable many to live. It is clear that in these cases the selection among the young hares is but little concerned with the number struggling for existence. The struggle here amounts to a struggle against the external conditions of life, not against numerous competitors of the same species.
Or, let us consider antelopes in an African steppe. Sometimes there is drought for many weeks; springs run dry, pools of water evaporate, many antelopes die of thirst. Only those remain alive which can bear thirst longest, or whose organs are so delicate as to enable them to sense the presence of water at great distances, better than the other antelopes. The struggle for existence here certainly produces an extensive selection, but it is a struggle against the external conditions of life, and has nothing to do with the number of antelopes. The quantity of water did not become insufficient because it was drunk by too many antelopes.
Another enemy of the antelopes is the lion. But the lion’s strength and cruelty do not depend upon the number of antelopes. There may even ensue a struggle between two lions for a single antelope, if there are not many antelopes, the stronger lion being victorious. But even this is of rare occurrence.
Far from being the general and constant cause of the struggle for existence, the great fruitfulness of certain organisms is rather a weapon enabling them to maintain themselves in this struggle, in which they would otherwise succumb. The struggle for existence, as a rule, is not a struggle between members of the same species when it has become too numerous, but a struggle of the individual or a group of individuals of the same species against the external conditions of life, which include not only the inorganic surroundings, but also the organic surroundings. Changes in these conditions of life also involve changes in the mode of the struggle for existence, in the method of using the organs; old organs or forms of organs become dispensable, new organs, or new forms of old organs, become necessary. If the species succeeds in evolving in the struggle with the new conditions, and thus becoming a new species, it will maintain itself; otherwise it will be destroyed. We may judge from remains found in the bowels of the earth how many such species have been destroyed in the earth’s history.
The theory of overpopulation proves nothing, therefore, against the assumption that the final cause for the formation of new species is in the changes of the conditions of life. Another view must still be mentioned: the view that acquired characteristics cannot be inherited.
Modern physiologists distinguish between the body cells and the reproductive cells, the “body plasm” and the “germ plasm”. The germ plasm, according to their view, is immutable, being transmitted again and again. But, according to Weismann, it is immutable even to the extent that it is not influenced by the qualities acquired by the body of the individual during his life. The individual cannot, therefore, transmit these acquisitions. Thus the formation of new, transmittable traits of species by the influence of new conditions of life on the body, is precluded. But this view was emphatically opposed, from its first appearance, particularly by Darwinists. Darwin, himself, assumed the heredity of acquired characteristics, as did also Herbert Spencer. Recent experiments show, on the one hand, that external influences do produce changes which are transmitted, and, on the other hand, that the germ plasm is by no means absolutely independent of the body plasm. This question is excellently treated by Tschulok in his little book on evolution; the following experiment is particularly interesting:
“Two races of hens were treated, one pure black, the other pure white. The races were pure, i.e., it was known definitely for each individual that its parents, grandparents and great-grandparents had all presented the same characteristics as the individual itself; in other words, that no mixture had taken place. When such a white hen was crossed with a white cock, their posterity were white exclusively. Similarly, mating a black hen with a black cock produced only black posterity.
“Now the following experiment was made:
“The ovary of a white hen was removed and implanted in the body of a black hen; the black hen’s ovary was also implanted in the white hen. The operation was performed so neatly that the animals remained alive and were capable, after the wounds had healed, of producing posterity by the normal methods. The white hen with the black ovary was now fructified by a black cock. We should here expect the posterity to be black, for the ova in the ovary of the white hen came from a black hen, and the male semen was likewise obtained from a black cock. However, the chickens were colored black and white. Similarly, the black hen, with an ovary taken from a white hen, was fructified by a white cock. The posterity included not only pure white chickens, but also chickens with black spots.” 
This result is the more astonishing in that it was attained by powerful mechanical interference, not by a gradual, organic alteration. The ovary in the body of the black hen had already attained full development when it was implanted in the white hen’s body, and yet the influence of the new body cells on the transferred germ cells was so strong as to enable the new body fully to impress its type upon the ovary. It might be assumed that the influence of changed somatic traits on the germ plasm must be still stronger in cases where the body suffers changes by reason of the influence of altered conditions, before its germ cells attain full maturity, with the result that the process of maturing goes on completely under the influence of the new properties.
We, therefore, see no reason that would oblige us to assume that acquired characteristics cannot be transmitted. The manner in which heredity works is, however, still completely hidden. Nor may we assume that all acquired characteristics are inherited. Lesions and mutilations, for instance, are hardly transmitted. Weismann cut off the tails of many generations of mice, without ever obtaining a tailless mouse. Many an apparent case of heredity may also be explained by the fact that the posterity live under the same conditions as their ancestors, and therefore acquire and present the same characteristics, without necessarily inheriting them.
There are many degrees among the inherited characteristics. Some are more persistent than others. There are inherited characteristics which the individual may easily lose if it enters a milieu deviating from that producing these qualities. Other traits, on the other hand, are stubbornly retained for many generations, even with the greatest variations in the conditions of life. Relatively, as compared with those traits that change easily, inherited traits of the latter kind may be considered immutable. But if they were acquired owing to the influence of special conditions of life, it would be impossible to understand why they should not be capable of changing under the influence of altered conditions of life.
Many scientists distinguish between race traits proper, in man, which are said to be absolutely unchanging, such as the color of the eyes, the hair, the skin, the shape of the skull; and secondary or fluctuating properties, such as bodily stature, bone structure, muscular system, fatty tissue, etc.
No doubt there is a difference between race traits of these two kinds. But perhaps this difference should be ascribed solely to the fact that the conditions bringing about the fluctuating properties are more susceptible and more swiftly susceptible to change than those causing the apparently immutable race traits. The former may change so quickly as to enable us to observe their influence without difficulty. The other conditions we do not even know, perhaps for the reason that they do not change perceptibly within the period of our observations. But we cannot say of any race trait that it is absolutely unchanging; such a trait would be the sole unchanging phenomenon in this changing world.
On this point, Fishberg says:
“Recent investigations have led to a modification or even complete abandonment of the theory of the constancy and persistence of race traits. For a long time, some anthropologists have maintained that the external environment, particularly the nutrition, the social and geographical surroundings, have a powerful influence on the modification of some traits, such as musculature, stature, etc. Many even go so far as to say that these agencies may alter pigmentation and head-form. Ridgeway, going further, assumes that the duration of human types in a certain region, and over long periods, is an expression not of the influence of heredity, but of environment, and that, on the other hand, modifications of the human form found in the Mediterranean region, and in central and northwest Africa, may be traced back to differences of climate, soil and national products.
“This theory of the decisive influence of environment on the alteration or modification of basic somatic traits may easily be applied to some of the race traits ... In some regions it has been found that the soil has a powerful influence on the stature of the inhabitants; for instance, the great height of persons inhabiting the State of Kentucky is very probably to be explained by the presence of hard water in this region. Similarly (according to Rose), the stature of the population in Gotha, Germany, has been undergoing changes since the introduction of hard water. Observations have also been made on the influence of environment on the head-form – a trait that has hitherto been considered immutable under all circumstances ...
“Professor Franz Boas, of New York, recently arrived at the conclusion, based on his investigations, that the absolute persistence of human types is an untenable theory. His investigations of the physical characteristics of immigrants have revealed an extremely interesting condition; he finds that the children of immigrants are of higher stature and better bodily development than their parents born in Europe. He has also discovered a very remarkable alteration in the head-form of children born in America after their parents had landed. Even a child born abroad, and not more than one year old on its arrival in America, will retain the foreign head-form. But a child born in America, though only a few months after the parents have landed, has the American head-form.” 
Other investigators before Boas had found that the whites in the United States acquire more and more Indian traits in the course of a few generations, thus becoming “Indianized”.
But it would be premature to infer from these facts that the American milieu will ultimately make Indians of the whites.
Even among animals, the milieu is only one of the circumstances determining somatic forms and physical these conditions will strength. Other things being equal, produce both; but these conditions also include the organism on which the milieu is working. The same milieu will not necessarily influence different organisms in the same way, but may have different effects on each. If various races are transplanted from the milieus producing them, into a new environment, they will all be changed by this environment, but not necessarily all in the same way.
The American conditions may have a different effect on a white man than on a Mongolian or on a Negro.
Other factors enter also, however, which make the race problem in the case of man much more complicated even than among animals.
1. Charles Darwin, The Variation of Animals and Plants under Domestication, London 1876, vol.i, pp.46, 46; vol.ii, pp.220, 222.
2. Charles Darwin, The Origin of Species, Harvard Classics Edition, Chap.iv, p.140.
3. Die Verbreitung der Tierwelt, Leipzig, 1902.
4. Brehm: Tierleben.
6. Tschulok, Entwicklungstheorie, Stuttgart, J.H.W. Dietz 1912.
7. Fishberg, German edition, pp. et seq.
Last updated on 20.1.2004