436 Mental Factors in Evolution 



If we include under the expression of the emotions not only the 

 premonitory symptoms of the initial phases of the organic and mental 

 state, not only the signs or conditions of half-tide emotion, but the 

 full-tide manifestation of an emotion which dominates the situation, 

 we are naturally led on to the consideration of many of the phe- 

 nomena which are discussed under the head of sexual selection. The 

 subject is difficult and complex, and it was treated by Darwin with 

 all the strength he could summon to the task. It can only be dealt 

 with here from a special point of view that which may serve to 

 illustrate the influence of certain mental factors on the course of 

 evolution. From this point of view too much stress can scarcely be 

 laid on the dominance of emotion during the period of courtship and 

 pairing in the more highly organised animals. It is a period of 

 maximum vigour, maximum activity, and, correlated with special 

 modes of behaviour and special organic and visceral accompaniments, 

 a period also of maximum emotional excitement. The combats of 

 males, their dances and aerial evolutions, their elaborate behaviour 

 and display, or the flood of song in birds, are emotional expressions 

 which are at any rate coincident in time with sexual periodicity. 

 From the combat of the males there follows on Darwin's principles 

 the elimination of those which are deficient in bodily vigour, deficient 

 in special structures, offensive or protective, which contribute to 

 success, deficient in the emotional supplement of which persistent 

 and whole-hearted fighting is the expression, and deficient in alert- 

 ness and skill which are the outcome of the psychological develop- 

 ment of the powers of perception. Few biologists question that 

 we have here a mode of selection of much importance, though its 

 influence on psychological evolution often fails to receive its due 

 emphasis. Mr Wallace 1 regards it as "a form of natural selection"; 

 " to it," he says, " we must impute the development of the exceptional 

 strength, size, and activity of the male, together with the possession 

 of special offensive and defensive weapons, and of all other characters 

 which arise from the development of these or are correlated with 

 them." So far there is little disagreement among the followers of 

 Darwin for Mr Wallace, with fine magnanimity, has always preferred 

 to be ranked as such, notwithstanding his right, on which a smaller 

 man would have constantly insisted, to the claim of independent 

 originator of the doctrine of natural selection. So far with regard 

 to sexual selection Darwin and Mr Wallace are agreed ; so far and 

 no farther. For Darwin, says Mr Wallace 2 , "has extended the 

 principle into a totally different field of action, which has none of 

 that character of constancy and of inevitable result that attaches 

 to natural selection, including male rivalry ; for by far the larger 



1 Darwinism, pp. 2iS2, 283, London, 1889. " Ibid. p. 283. 



