SEXUAL SELECTION. 209 



Our difficulty in regard to sexual selection lies in understand- 

 ing how it is that the males which conguer other males, or those 

 which prove the most attractive to the females, leave a greater 

 number of offspring to inherit their superiority than their beaten 

 and less attractive rivals. Unless this result does follow, the 

 characters which give to certain males an advantage over others, 

 could not be perfected and augmented through sexual selection. 

 When the sexes exist in exactly eaual numbers, the worst-en- 

 dowed males will (except where polygamy prevails), ultimately 

 find females, and leave as many offspring, as well fitted for their 

 general habits of life, as the best-endov/ed males. From various 

 facts and considerations, I formerly inferred that with most ani- 

 mals, in which secondary sexual characters are well developed, 

 the males considerably exceeded the females in number; but this 

 is not by any means always true. If the males were to the fe- 

 males as two to one, or as three to two, or even in a somewhat 

 lower ratio, the whole affair would be simple; for the better- 

 armed or more attractive males would leave the largest number 

 of offspring. But after investigating, as far as possible, the nu- 

 merical proportion of the sexes, I do not believe that any great 

 inequality in number commonly exists. In most cases sexual 

 selection appears to have been effective In the following manner. 



Let us take any species, a bird for instance, and divide the fe- 

 males inhabiting a district Into two equal bodies, the one con- 

 sisting of the more vigorous and better-nourished individuals 

 and the other of the less vigorous and healthy. The former, 

 there can be little doubt, would be ready to breed In the spring 

 before the others; and this is the opinion of Mr. Jenner Weir, 

 who has carefully attended to the habits of birds during many 

 years. There can also be no doubt that the most vigorous, bes[- 

 nourlshed and earliest breeders would on an average succeed iu 

 rearing the largest number of fine offspring.' The males, as ws 

 have seen, are generally ready to breed before 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 



' Here is excellent evidence on the character of the offspring from 

 an experienced ornithologist. Mr. J. A. Allen, in speaking ('Mam- 

 mals and Winter Birds of B. Florida,' p. 229) of the later hroods, atter 

 the accidental destruction of the first, says, that these "are found to 

 "be smaller and paler-colored than those hatched earlier in the sea- 

 "son. In cases where several broods are reared each year, as a gen- 

 "eral rule the birds of tlie earlier broods seem in all respects the 

 "most perfect and vigorous." 



^ Hermann Muller has come to this same conclusion with respect 

 to those female bees which are the first to emerge from the pupa 

 15 



