ORGANIC EVOLUTION—-MACNAMARA., 869 
persistence. These traces of ancestral history are intelligible only by 
means of the hypothesis of natural selection. 
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.* 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.* 
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,‘ 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.’ 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. On 
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.® 
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 
1 Heredity, by Prof. J. A. Thomson, p. 127. 
2 British Association for the year1911. Sec. D. ‘The Origin of Mammals.’’ 
8 Prof. H. E. Crampton, “‘The Doctrine of Evolution,’’ p. 175. Human Speech, by N. C. Macnamara, 
p. 210, figs. 37 and 42. 
4 Huxley’s Essays, p. 100. 
5 Huxley’s Essays, p. 228. 
6 J, A. Thomson on Heredity, pp. 338, 387. 
38734°—sm 1911——24 
