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’ 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?, “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. 282, 283, London, 1889. 2 Tbid. p. 283. 
