OBGANIC EVOLUTION MACNAMARA. 369 



persistence. These traces of ancestral history are intelligible only by 

 means of the hypothesis of natural selection. 1 



Prof. G. Elliot Smith insists on the fact that a knowledge of the 

 evolution of the brain affords us a reliable and important clue in 

 understanding the factors which have led to the making of mammals 

 what they are, as well as supplying evidence to show whence they 

 came. He demonstrates the fact that from the earliest development 

 of the structures forming the cerebral cortex (or that portion of it in- 

 cluded in the neopallium), its function has been to regulate "skilled" 

 movements of the animal's body. 2 The superior development of 

 the brain of Pithecanthropus with its rudimentary sensori-motor 

 center of speech, gave this order of beings an advantage over its 

 nearest competitors, the anthropoid apes, and as the progressive evo- 

 lution of the brain of man was raised to a higher standard by the 

 exercise of his skilled movements, so his psychical powers increased, 

 and led him to manufacture weapons and implements of various 

 kinds, and to appreciate the use of fire to aid his brute force. 

 Thus the gap between man and apes widened more and more as the 

 reasoning power of the former increased through successive gen- 

 erations. 3 



Having thus given an outline of the evidence which leads us to 

 accept Darwin's hypothesis as being as near an approximation to the 

 truth as, for example, the Copernican hypothesis was to the true theory 

 of the planetary motions, 4 we must refer to some of the reasonable 

 objections that have been advanced against this theory. 



As far back as the year 1863 Huxley found he was unable, without 

 reserve, to accept the theory of natural selection, because although in 

 his opinion this theory accounted for the structural origin of species, 

 it was incapable of explaining their physiological differences. 5 For, 

 he argued, it was a well-known fact that distinct species in a state of 

 nature were, when crossed, incapable of perpetuating the species. Qn 

 the other hand, selective breeding was incapable of producing species 

 which on crossing were, as a rule, sterile. Since Huxley's time, 

 however, it has been proved that fertile pairing between distinct 

 species of animals is by no means a rare occurrence. 6 



We have already referred to another difficulty experienced by 

 many educated people in accepting, without reserve, the theory of 

 natural selection; they are unable to conceive how slight beneficial 



i Heredity, by Prof. J. A. Thomson, p. 127. 



2 British Association for the year 1911. Sec. D. " The Origin of Mammals." 



3 Prof. H. E. Crampton, "The Doctrine of Evolution," p. 175. Human Speech, by N. C. Macnainara, 

 p. 210, figs. 37 and 42. 



4 Huxley's Essays, p. 100. 

 6 Huxley's Essays, p. 228. 



6 J. A. Thomson on Heredity, pp. 338, 387. 



38734°— sm 1911 24 



