EVOLUTION 



3033 



EVOLUTION 



life is widened and its agency be- 

 comes more free. In a sense, the 

 behaviour of a ciliated infusorian 

 is just as perfect as that of a bird, 

 but the range is narrower, and the 

 resources are fewer. The behaviour 

 of ants and bees is extraordinarily 

 effective on the instinctive line (see 

 Instinct), and in its way unsur- 

 passable. It cannot be profitably 

 pitted against the behaviour of a 

 horse or a dog, which is on the in- 

 telligent line, but its range re- 

 sources are narrower. The instinc- 

 tive creature is apt to be sadly non- 

 plussed by some slight alteration in 

 the routine of its experience. What 

 Sir Ray Lankester has called the 

 " little-brain " type, rich in inborn 

 or instinctive capacities but slow 

 to learn, must be distinguished 

 from the " big-brain " with little 

 ready-made equipment, but with 

 prodigious educability. 



The "big-brain" type came to 

 its own in birds and mammals, 

 and there convincing evidence is 

 found of an inner mental life of 

 subjective experimenting, called 

 perceptual inference, or intelli- 

 gence. Interesting also is the fact 

 that, as an organism attains to 

 complex efficiency and to more or 

 less intelligent mastery of its en- 

 vironment, it is able to practise 

 reproductive economy. There are 

 fewer offspring, but there is less 

 mortality. 



Emergence of Man 



In the Early Eocene age, perhaps 

 three million years ago, there 

 emerged an arboreal race, the 

 Primates, differentiated from other 

 mammals in digits, teeth, skull, and 

 brain. From this stock there 

 diverged in succession the New 

 World monkeys, the small anthro- 

 poid Apes (gibbon and siamang), 

 and the large anthropoid Apes 

 (orang, chimpanzee, and gorilla). 

 This left towards the end of the 

 Oligocene (or perhaps in the 

 Miocene) a generalised human stem, 

 from which there diverged in suc- 

 cession Pithecanthropus the erect, 

 the slouching man of Neanderthal, 

 and the early Briton of the Sussex 

 Weald known by the famous 

 Piltdown skull. None of the off- 

 shoots came to much, it seems, 

 but the main stem continued as the 

 stock of modern man, broken up in 

 relatively recent times into African, 

 Australian, Mongolian, and Euro- 

 pean races. 



With the emergence of Man 

 evolution passed on to another 

 grade. For there are several 

 reasons for avoiding the false sim- 

 plicity of regarding social evolution 

 as no more than a continuation of 

 infra-human evolution. The first 

 and chief reason is to be found in 

 man's undeniable apartness and 



pre-eminence as a rational and 

 social person. Man is differentiated 

 by his language, by his capacity for 

 forming and experimenting with 

 general ideas, i.e. by his reason , by 

 his vivid self-consciousness of his 

 own evolution and by purposeful 

 determination to control it ; and by 

 his strong kin-instincts. The second 

 reason is the fact that in social 

 history we have to deal with 

 integrates of social persons, oper- 

 ating as unities of a higher order. 

 The third reason is the importance 

 of what lies outside the individual, 

 namely, in literature and art, the 

 folk-ways of customs and tradition, 

 the external registrations which we 

 call institutions. In all this new 

 notes are struck, and the evolution 

 of man, though continuous with, is 

 more than a mere continuation of, 

 the evolution that goes on in infra- 

 human animate nature. 



Factors in Organic Evolution 



While the general idea of 

 evolution is accepted by most 

 naturalists, there is great un- 

 certainty in regard to the operative 

 factors. The uncertainty is partly 

 due to the difficulty of arguing 

 from a meagre experience of the 

 present to a past of many millions 

 of years, and partly to the fact that 

 the inquiry is still very young, for 

 it virtually dates from Darwin's 

 Origin of Species, 1859. 



There are two main problems. 

 The first asks how the continual 

 emergence of new things, 8f 

 changes or variations which make 

 an organism appreciably different 

 from its parents or its kin, is to be 

 accounted for. The second asks 

 what directive factors may operate 

 on the variations which arise, deter- 

 mining their elimination or persist- 

 ence and working towards the 

 familiar but puzzling result the 

 existence of distinct and relatively 

 well-adapted species. 



Some of the peculiarities or 

 observed differences distinguish- 

 ing members of the same species 

 can be shown to be individually 

 acquired bodily modifications di- 

 rectly due to some peculiarity of 

 nurture in the widest sense. But 

 as there is no secure evidence that 

 these characteristics are trans- 

 mitted to the offspring, they can 

 only be of indirect importance to 

 the race. The raw material of 

 evolution is furnished not by these 

 modifications, but by variations 

 which are inborn, not acquired or 

 imposed from without. 



Among these variations there 

 may be distinguished minute pecu- 

 liarities, and larger abrupt sports of 

 notable amount, such as a fantail 

 pigeon or a copper beech. The 

 former, Darwin's " individual vari- 

 ations," may be usefully termed 



fluctuations. The sports corre- 

 spond to Galton's " transilient vari- 

 ations," Bateson's " discontinuous 

 variations," De Vries's " muta- 

 tions," and the last term should be 

 kept for them. The transmissibility 

 of inborn fluctuations has been 

 proved in a few cases, and it was 

 Darwin's conviction that " it is 

 by the accumulation of such ex- 

 tremely slight variations that new 

 species arise." 



As to the origin of those minute 

 novelties, a falling out of some 

 feature, or a rearrangement of 

 certain characters displayed by 

 ancestors, it is possible to think of 

 them as due to the intricate permu- 

 tations and combinations that 

 occur in the germinal material in 

 the history of the germ -cells, 

 especially during maturation and 

 fertilisation (see Embryology) 



But the baffling problem is the 

 origin of the distinctively new, 

 where the novelty is qualitative, 

 not quantitative, where a new 

 pattern, like a genius, appears. At 

 present science cannot go beyond 

 tentative suggestions. Some facts 

 suggest that environmental influ- 

 ences may act as variational stimuli 

 on the germ-cells and provoke 

 mutation. It is also known that 

 one species may differ from another 

 in the number, shape, size, and 

 structure of its nuclear bodies or 

 chromosomes, and just as bacteria 

 sometimes change suddenly in 

 their physiological properties, so 

 the chromosomes which last on 

 from generation to generation may- 

 change in their stereochemic archi- 

 tecture or functional powers. 

 Germ-cells and Variations 

 This again might be due to environ - 

 mental influence or to processes of 

 ageing or rejuvenescence occurring 

 in the germ -cells. Just as a remark- 

 able regulatory process, called 

 endomixis, takes place periodically 

 in a " pure line " of slipper- 

 animalcules (i.e. in a stock all 

 descended from one individual), so 

 in a lineage of germ -cells, within 

 the organism that bears them, a 

 similar process might occur. 



It must be borne in mind that a 

 germ -cell is no ordinary cell, but 

 an organism telescoped down into 

 a one-cell phase of its being. Just 

 as a Protozoon may make experi- 

 ments as well as a Mammal, so the 

 germ-cells may conceivably make 

 architectural experiments in self- 

 adjustment or self-expression, the 

 outcome being seen in variations. 



The most clearly discerned 

 directive factor in organic evolu- 

 tion is natural selection, the pro- 

 cess by which, in the struggle for 

 existence, certain variants of a 

 species, marked from their fellows 

 by the presence or absence of some 



