1022 LIFE : OUTLINES OF GENERAL BIOLOGY 



in over-destructiveness. In regard to some of the questions involved, 

 the wisest course is probably to suspend judgment until fresh facts, 

 especially of an experimental kind, accumulate. In regard to some 

 other implications, however, it seems possible to meet some of the 

 chief objections by a re-statement in the light of new data. 



It was primarily in reference to secondary sex-characters that 

 Darwin suggested his theory of sexual selection. Certain variations, 

 e.g. in the improvement of weapons and food-catching apparatus, 

 are favoured by natural selection in the course of the everyday 

 struggle for existence; in the same way, variations which are 

 advantageous in securing mates and consummating sexual repro- 

 duction will be favoured by sexual selection. 



Darwin began with instances of the importance of masculine 

 vigour and equipment when rival males compete for the possession 

 of the females. "The strongest, and with some species the best- 

 armed of the males, drive away the weaker; and the former would 

 then unite with the more vigorous and better-nourished females, 

 because they are the first to breed. Such vigorous pairs would surely 

 rear a larger number of offspring than the retarded females, which 

 would be compelled to unite with the conquered and less powerful 

 males, supposing the sexes to be numerically equal; and this is all 

 that is wanted to add, in the course of successive generations, to 

 the size, strength, and courage of the males, or to improve their 

 weapons." (Descent of Man, 2nd ed., 1888, vol. i, p. 329.) 



Now it is plain that forceful competition among rival males for 

 the possession of a female or of several females, does not differ in 

 kind from the ordinary struggle for food and foothold, except that 

 it is strictly intra-specific. Darwin pointed out indeed (p. 349) that 

 sexual selection is less rigorous than natural selection; that it is less 

 of a life-and-death affair; that it operates through the unsuccessful 

 males having fewer, less vigorous, or no offspring ; and that it is not 

 limited by the general conditions of life; but there is in all this no 

 departure from the general logic of the theory of natural selection. 

 This part of the theory, therefore, remains valid to those who 

 regard natural selection as a vera causa. 



Darwin went on to those characters that are useful in the recog- 

 nition and capture of the females. When a male excels his neighbours 

 in his capacities for finding, pursuing, and catching the female, 

 sexual selection, he said, again comes into action. (Descent of Man, 

 p. 324.) The male moth often finds his mate by the olfactory acute- 

 ness of his large antennae ; some small crustaceans recognise the other 

 sex almost instantaneously when there is chance contact in the 

 water; in some fishes, recognition depends on colour and on 

 behaviour; many experiments led Goltz to believe that the male 

 frog distinguishes the female by touch ; in birds, visual and auditory 

 impressions count for most ; in mammals, the scent is often of chief 



