CHAPTER II

EVOLUTION OR DESCENT OF LIVING ORGANISMS The theory of evolution is intimately associated with the name of _Darwin_, for it was he who established it in the scientific world. In reality, the idea of the transformation of organisms was put forward by _Lamarck_ more than a century ago, but he did not sufficiently support it. The theory of evolution states that the different animal and vegetable species are not each of them specially created as such from the first, but that they are connected with each other by a real and profound relationship, and derived progressively one from another; generally from more simple forms, by engraphia and selection. Man himself is no exception to this rule, for he is closely related to the higher apes. It is no longer possible to-day to deny the fundamental fact which we have just stated. Since _Darwin_, and as the result of the powerful impulse which this man of genius gave to natural science, innumerable observations and experiments have confirmed the truth of the progressive evolution of living beings. Comparative anatomy, comparative geography of plants and animals, comparative embryology, and the study of the morphology and biology of a number of recently discovered plants and animals, have built up more and more the genealogical tree, or _phylogeny_, of living beings, that is to say their ancestral lineage. The number of varieties and races or sub-species increases indefinitely, the more closely they are examined. Researches on the fossil remains of species of animals and plants which have been extinct for thousands and millions of years (_palæontology_) have also contributed to determine the trunk of the great tree of former life. The numerous gaps which still exist between these fragmentary documents of former ages are nevertheless too considerable for continuous connections to be established in the past by the aid of fossils. We not only know that the different forms of living beings are connected to each other by a real relationship, but we can fathom more and more deeply the degrees of this relationship, and can often prove from which group of animals a given group is descended. In many cases we can determine at which period the fauna and flora of two continents have been separated from each other, and in what manner they have been transformed, each in its own way, while still preserving the general characters which were common before their separation. The specialist can soon discover what species belong to the old geographically differentiated fauna and flora of the country, and what have been ulteriorily imported. I record these facts for the benefit of those persons who have not yet understood that it is absolutely useless at the present day to dispute the evolution of living beings. Deceived by the divergent opinions of scientists concerning hypotheses which endeavor to explain the details of evolution, these persons confound the details with the fundamental facts of evolution. =Ontogeny. Phylogeny.=--In the light of the facts of evolution, heredity takes quite a new aspect when removed from the old biblical idea of the independent creation of species. _Haeckel_ launched into the scientific world, under the name of "fundamental biogenetic law," a theory which, without having the right to the title of an immutable dogma, explains the facts in a general way, and gives us a guiding line along the phylogenetic history of living beings. "_Ontogeny_," that is the history of the embryological development of each individual, always consists in a summary and fragmentary repetition of _phylogeny_, or the history of the ancestors of the species to which the individual belongs. This signifies that, as embryos, we repeat in an abridged form the series of types or morphological stages through which has passed the series of our animal ancestors, from the primitive cell to man. In reality this is only true in a relative way, for a considerable part of the ancestral engraphias of the embryo has disappeared without leaving any trace; also many embryos, especially those which have special conditions of existence outside the body of their mother, have acquired special complex organs and corresponding functions. Thus, the caterpillars of butterflies with their specific and generic peculiarities, hairs, horns, etc., furnish many examples of secondary acquired characters which have nothing in common with the worm, which is the ancestral type of the butterfly represented by the embryonic period when it is a caterpillar. However, many undoubted vestiges of the ancestral history are found in the embryos at different periods of their development. It is certain that insects descended from worms, and there is no doubt that the larvæ of insects, which are almost worms, represent the ontogenetic repetition of the phylogeny of insects. It is also certain that whales, although they have whalebone instead of teeth, have descended from cetacea provided with teeth, which in their turn descended from terrestrial mammals. But we find in the embryo whale a complete denture which is of no use to it, and which disappears in the course of the embryonic period. This denture is nothing else than a phylogenetic incident in the ontogeny of the whale. In the fins of cetacea, as in the four limbs of other mammals, we find the same bones, which are derived from the bones of the wings and legs of their bird ancestors. In birds, the same bones are the phylogenetic derivatives of the limbs of reptiles. All these facts demonstrate with certainty the descent of animal forms, a descent which we can follow in all its details. In certain ants whose bodies show their close relationship with a slave-keeping group, but which have become the parasitic hosts of other ants, we find not only the arched mandibles, shaped for rape, but the undoubted rudiments of the slave instinct, although this instinct has, perhaps, not been exercised by them for thousands of years. These examples suffice to show that the form and functions of a living organism, as well as its mental faculties, are derived not only from the most recent direct ancestors of this organism, but that they partly mount much higher in the genealogical tree. Our coccyx is a vestige of the tail of animals. It is from them also that we have inherited anger and jealousy, sexual appetites, fear, cunning, etc. As long as they remain in use, the oldest inherited characters normally remain the most tenacious and are preserved the longest. When they cease to be utilized, or become useless, they still remain for a long time as rudiments before finally disappearing; for instance the vermiform appendix of the intestine and the pineal gland of the brain. These rudiments often persist for still a longer time in the embryo, as we have seen in the case of the ancestral teeth of the embryo whales. We also meet with the stumps of wings in the chrysalis of certain ants (_Anergates_), the males of which have lost their wings. =Natural Selection.=--The artificial selection practiced by gardeners and cattle breeders led _Darwin_ to his hypothesis of natural selection by the struggle for existence. Confirmed in his idea by the observation of tropical nature, _Darwin_ thought he could explain the origin of living beings by natural selection. It is this hypothesis which is properly called _Darwinism_. But the name Darwinism has also been given to evolution as a whole, which has been the cause of endless confusion. All the mystic and narrow-minded, full of biblical prejudice, naturally profit by this confusion to attack the facts of evolution and science itself. =The Struggle for Existence.=--The struggle for existence and natural selection are absolutely positive facts, which can be constantly verified by the observation of living nature as it is presented to us. All living beings eat one another or at any rate struggle against each other, plants as well as animals; and, apart from air and water, animals are almost entirely nourished by plants and other animals. It is obvious that in this perpetual struggle the less adapted and the less armed--and by arms we include the powers of reproduction, resistance to diseases and to cold, etc.--disappear, while the better adapted and the better armed persist. I confess I cannot understand the detractors of _Darwin_ who are blind in face of these facts and hypnotized by certain conventional suggestions. On the other hand, what always has been and still remains hypothetical is the explanation of the descent of all plants and animals by natural selection alone. We have already spoken of the _mutations_ of _de Vries_, and the theory of the _mneme_ elaborated by _Semon_, and need not repeat them here. Thanks to the idea of _Hering_, worked out by _Semon_, the facts are now explained in a satisfactory manner. Engraphia, produced in the organisms by the irritating agents of the external world, prepares and builds up little by little their increasing complications, while selection, by continually eliminating the unfit, directs the elaborating work of the mneme and adapts it to the surrounding local circumstances. _De Vries_ has objected that the variations produced by artificial and natural selections are mutable, while sudden mutations have a much more stable character. But we have just seen that these mutations themselves are evidently only the delayed ecphoria of a long ancestral engraphia accumulated. On the other hand, the variations obtained by selection are themselves only due to more rapid ecphorias, derived from repeated conjugations in a certain direction. _Plate_ and others have shown that they may become more and more fixed, if they are well adapted, and thus become more tenacious. There is, therefore, no contradiction between the fundamental facts, and all is simply and naturally explained by the combination of hereditary mnemic engraphia with selection. Recent study on the transformations of living beings have shown that they do not take place in a regularly progressive manner, as _Darwin_ at first believed, but that periods of relatively rapid transformation alternate with periods of relative arrest, both in a general way and for each particular species. We see certain species remaining almost stationary for an immense time and tending rather to disappear, while others vary enormously, showing actual transformation. The transplantation of one species to a new environment, for instance to a new continent, provokes, as has been proved, a relatively rapid transformation. It is evident that mnemic engraphia transforms organisms the more rapidly as it changes in nature itself, which is the case in the migrations we have just mentioned, and which also changes the factors of selection. Other facts show clearly that the fauna and flora of the present world find themselves in a period of recoil with regard to their modification. In the tertiary period the fauna and flora of the world were richer than to-day; many more older species have disappeared than new ones have arisen. This fundamental fact seems due to the extremely slow cooling of the earth, and appears to be indicated by the powerful growth in tropical climates, the fauna and flora of which resemble those of the tertiary period, and, on the other hand by the relative poverty and slowness of growth in cold countries. =Conclusions.=--What are the principal conclusions to which we are led by this short study of the ancestral history or phylogeny of man? (1). The transformation or evolution of living beings is a demonstrated fact. (2). The factors in evolution appear at first sight to be very diverse: selection, mutation, climatological, physical and chemical factors, etc. We have seen that they may all be connected with the fundamental principle of mnemic engraphia, aided by natural selection. No doubt the nature of the mnemic engraphia of external agents in the living substance is still unknown. When we are able to connect the laws of life with the laws of inert nature, we shall only have before us a single great metaphysical mystery, that of the tendency of mundane energy to the differentiation of details and the production of complicated forms. What is important here is to know that engraphia and selection are capable of considerably modifying species in a positive or negative manner, for good or evil, improving them by good influence and good conjugations, or deteriorating them by bad selection or by blastophthoria, which causes them to degenerate. The combination of a bad selection with blastophthoric influences constitutes the great danger for humanity, and it is here that a rational sexual life should intervene. (3). The mental faculties of animal species, as well as their physical characters, depend on their ancestral hereditary mneme. They simply represent the internal or introspective side of central activity, and the brain obeys the natural laws of the mneme in the same way as the other organs. (4). It follows from all this that phylogeny and selection, the same as heredity properly understood, have the right to a fundamental place in the sexual question, for the germs which, after each conception, reproduce an individual are, on the one hand, bearers of the inherited energy of our ancestors, and on the other hand, that of future generations. According to the care or neglect of civilized humanity they may be transformed for good or evil, progress or recede. Unfortunately, owing to religious and other prejudices, the question of evolution is not discussed in schools. Hence, the majority of men only hear of these things by hearsay in a rough and inexact manner; so that a series of phenomena familiar to naturalists and medical men, are still dead letters for the rest of the public. This obliges me to speak further on some points of detail. The so-called historical times, that is the times of the Chinese, Egyptians and Assyrians, which appear to us extremely remote, are from the point of view of evolution very near to us. These ancient peoples, at any rate those who were our direct ancestors, or who were closely related to them, are thus, in the language of evolution, which takes no count of time or of the number of generations, our very near relations. The generations which separate them from us and the few hundred generations between them and those of their direct ancestors, who were at the same time ours, represent a limited period from the point of view of the ethnological history of mankind. On the other hand, if we examine the savage peoples of America, Asia, Africa and Australia, which have been specially studied since the discovery of America and some of which are actually living, and compare them with ourselves and with our ancestors of four thousand years ago, we find that they differ infinitely more from us than we differ from our ancestors, as their ethnographical and historical remains are sufficient to prove. Among the savage peoples we find races such as the pigmies of _Stanley_ (Akkaas), the Weddas of Ceylon, even Australians and negroes, whose whole bodily structure differs profoundly from our European race and its varieties. The profoundness and constancy of these differences clearly show that the relationship of such races to ours must be very remote. We are concerned here with veritable races or sub-species, or at least with very constant and accentuated varieties. It is true that it is difficult to unravel the almost inextricable confusion of human races; but we may be certain that the savage races and varieties remote from ours, and even certain less-remote races such as the Mongols and Malays, are, phylogenetically speaking, infinitely less related to us than the ancient Assyrians. This indicates that the ancestors which were common to us and these races must probably be looked for several thousands of generations back, even when their descendants are still living on other continents at the present day. It is easy to explain that human races so different could develop separately in continents and under climates with a very different mode of life and conditions of development, if we reflect that at these remote periods men only had very limited modes of transport and lived in a fashion very little different from that of the anthropoid apes, so that the ethnological forms were preserved separated from each other by small distances. This fact can still be observed among the small hostile Indian or Malay tribes, who live in tropical regions and often occupy only a few square leagues. The higher civilizations of former times could not develop beyond a comparatively limited circle, as their means of transport did not allow them to venture too far. The conquest of the whole earth by modern civilization by means of the mariner's compass, firearms, steam and electricity is thus an absolutely contemporaneous event, unique in the history of the world, the origin of which hardly goes back more than four hundred years. This event has completely upset the natural internal evolution of human races, by the fact that all the lower races attacked by civilized races armed with guns and alcohol, are destined to rapid and complete destruction. Geology has discovered in the caves of the quaternary period, human remains which are much lower in the scale of evolution and much nearer the anthropoid apes than the lowest races still living. Their brain, as shown by the cranial cavity, was still smaller. Lastly, _Dubois_ has discovered in Java the cranium of _Pithecanthropus erectus_ which is intermediate between that of the orang-utan and man. If more such remains are discovered the chain of transition between the apes and man will be almost complete. =Hybridity. Consanguinity.=--Before concluding this chapter we must study the question of _hybrids_. It is important to know to what point fecundity and descent are influenced by the degree of relationship between the two procreators. Conjugation probably arises from the general necessity of organisms to reënforce their race by variety. Consanguinity perpetuated is harmful to the species, in the same way as parthenogenesis, or indefinite reproduction by fission or budding. It produces enfeeblement and degeneration of the race, and leads to extinction by causing sterility. By _consanguinity_ is meant continued sexual union between near relatives. It is easy to understand that the conjugation of two germs derived from brothers and sisters or from a father and his daughter approaches parthenogenesis from the point of view of the mixing of hereditary energies. We shall see later on that nearly all peoples have a certain repugnance to consanguineous marriages. Among animals, natural selection eliminates too consanguineous products. On the other hand, sexual union between different species, however little removed, gives no products. Near species may produce hybrids between themselves, but these hybrids are as a rule sterile or nearly so, and are incapable of perpetuating their type, which reverts rapidly to one of the primitive species. It has been recently demonstrated that the incapacity of two species of animals to produce hybrids is intimately connected with the reciprocal toxicity of their blood. When the blood of one species is injected into the veins of another the production of hybrids is possible between them, at least as far as has been observed. It is curious to note that the blood of the anthropoid apes is not toxic for man, although these animals are very different from us, and hybrids have not yet been produced. This fact helps us to understand how it is that the differences which exist between the different human races do not prevent the production of hybrids between any two of them. In spite of this we may state, without risk of error, that the most dissimilar human races give a bad quality of hybrids, which have little chance of forming a viable mongrel race. We have not sufficient information on this point concerning the lowest human races, such as the pigmies and Weddas. On the other hand, mulattoes (hybrids between negroes and whites) constitute a race of very bad quality and hardly viable, while the hybrids between Indians and whites are much more resistant and of relatively better quality. In this question, the middle course appears without any doubt the true one. Unions between near races and varieties, or at least between individuals of the same race or variety whose relationship is old, are certainly the best. We readily grant that the homogeneity of a race has the advantage of fixing its peculiarities in a more durable and characteristic fashion; but many inconveniences counterbalance this advantage. If we one day, by wise selection and by eliminating all sources of blastophthoria obtain a superior quality of human germs, it is possible that in the remote future, consanguinity, provided it is not exaggerated may lose its dangers.