The answer is found in the selective influence of environment. There is an endless diversity of environments. The iceberg, the hot spring, the mountain top, the abysses of the ocean, the interior of another creature, all constitute a complex of changing influences. In many cases where the external changes are regularly recurrent like the seasons and the tides, the organism falls into step with them so that there are internal rhythms. To some of these changes the living organism is able to adjust itself temporarily. To others the response is not so delicate and the novel conditions provoke structural changes from which the organism never recovers, the limits of organic elasticity having been passed. Adaptation is the key-note of organic nature, and it is exactly the thing natural selection secures. However modified, those individuals which are not adapted to their environment are destroyed in the struggle for existence, leaving only the well-adapted forms alive. The environment molds the living organism. Those whose innate plasticity is equal to the occasion are modified and survive. Those whose plasticity is not equal to the occasion are exterminated. This modification takes place generation after generation, but, as such, is not inherited. But any variations arising in the germ cells which are similar. in direction to these modifications, will tend to support them, and to favor the organism in which they occur. Thus plastic modification leads, and germinal variation (variations arising in the germ cells) follows; the one paving the way for the other. The modification is not inherited, but it establishes a condition under which congenital variations 10 are given time to get a hold on the 10 Congenital variations are variations which arise in the germ cell. They are variations which are inherited. They are not modifications. organism, and are thus enabled by degrees to reach the fully adaptive level. Natural selection cuts off the unadapted individual. The plastic individual though originally unadapted to its particular environment, may be modified in such a manner that it survives. Of its offspring those who are plastic and adaptable survive, all others perish. But if one among its offspring possesses a germinal variation which better adapts it to the surrounding conditions, it immediately has an advantage in the struggle, and its progeny will inherit the favorable quality. These offspring which possess an innate adaptation will have a much better chance for longer life and larger families than those which possess mere plastic modifiability. In this way, during the evolution of life from low to higher and higher forms, Nature has weeded out and exterminated the ill-adapted organisms, tolerating the temporary compromise of modification until the progress of reproduction shall give rise to a real germinal variation (mutation) which brings renewed stability to the species. SUPPLEMENTARY READINGS. BOAS, F.-The Mind of Primitive Man. DARWIN, C.-The Origin of the Species. DAVENPORT, C. B.-Heredity in Relation to Eugenics. GALTON, F.-Natural Inheritance. KELLICOTT, W. E.-The Social Direction of Human Evolution. METCALF, M. M.-Organic Evolution. PUNNETT, R. C.-Mendelism. Since modifications do not seem to be inherited, it follows that the only kind of variations which count in the offspring are germinal variations. Mutations or stable variations are germinal variations and are therefore of more importance in evolution than fluctuating or unstable variations which are not transmitted to offspring. See Metcalf, pp. 82-86. ROMANES, G. J.-Darwin and After Darwin, I The Darwinian Theory. THOMSON, J. A. & GEDDES, P.-Evolution (Home University Library). THORNDIKE, E. L.-Individuality. WEISMANN, A.-The Evolution Theory. III THE ORIGIN AND ANTIQUITY OF MAN SINCE We explain the origin of different forms of animal life by adaptive modification and descent, it is only one step further to apply the same reasoning to the human species and to account for man as descended from some lower animal form now extinct. Darwin advanced this theory in his, "Descent of Man." Since Darwin wrote there has been much evidence gathered to support the doctrine of descent. The evidence of evolution is now based upon the discoveries of the explorer, paleontologist, anatomist, embryologist, and physiologist. Most natural scientists regard this body of testimony as constituting a confirmation of the theory of evolution. For certain forms of life it is indeed, quite conclusive.1 In this chapter, we shall concern ourselves with an examination of the chief evidences for the doctrine that man is descended, in common with other animals now living, from some lower and extinct form. The success of any demonstration that man is related by descent to some lower creature depends largely upon our ability to reconstruct the series of related forms. When the doctrine of the descent of man was first advanced, superficial and popular writers immediately jumped at the conclusion that naturalists believed that man was descended from the "monkey." This, of 1 But this is a matter that the reader can look up for himself in the many books now available upon the subject. course, is quite absurd, as man could obviously not be descended from a form of life now living. The ape and the monkey family, together with man, are probably descended from some generalized ape-like form long since perished from the earth. They both may have a common ancestor: one is not descended from the other. The human species or Hominidæ is not descended from the Gorilla or the Chimpanzee, but the ascent of the Hominidæ is in an independent line from some long since extinct generalized form, from which the other branches also spring in independent lines. All have some features in common, while each presents some special characters. The points of resemblance between the Hominidæ and the Simiida are far more numerous than between the Hominidæ and any other group. Keane infers from this that the divergence of the higher groups took place in the sequence indicated in the following classification. For this reason the study of man from the physical side is confined to his relation to the higher apes.3 It has been customary in modern zoölogical classification to detach from the Class Mammals, the large and dispersed group of Apes and Half-Apes (Lemurs), to constitute the independent order of Primates, so named by Linné. Recent systematists divide the order into two suborders, Lemuroidea and Anthropoidea, and subdivide the Anthropoidea, the manlike forms, into five familiesHapalida, Cebida, Cercopithecida, Simiida, and Hominida (human species). The reasons for asserting that men are primates and are closely related to the Simiida, are, that part for part the skeletons, pelvis, ribs, hands, feet, spinal columns, teeth, and bones of the skull, are 2 Keane, A. H.-Ethnology, 1896, p. 19. 3 Ibid., p. 20. 4 Ibid., p. 17. |