448 Tlie Descent of Man. Part W. 



without distinct evidence in each case, I am unwilling to admit 

 that this has been effected in natural species. On the other 

 hand, by means of successive variations, which were from the 

 lirst sexually limited in their transmission, there would not be 

 the least difficulty in rendering a male bird widely different in 

 colour or in any other character from the female; the latter 

 being left unaltered, or slightly altered, or specially modified for 

 the sake of protection. 



As bright colours are of service to the males in their rivalry 

 with other males, such colours would be selected, whether or 

 not they were transmitted exclusively to the same sex. Conse- 

 quently the females might be expected often to partake of the 

 brightness of the males to a greater or less degree; and this 

 occurs with a host of species. If all the successive variations 

 were transmitted equally to both sexes, the females would be 

 indistinguishable from the males; and this likewise occurs with 

 many birds. If, however, dull colours were of high importance 

 for the safety of the female during incubation, as with many 

 ground birds, the feniales whicll^ varied in brightness, or which 

 received through inheritance from the males any marked ao- 

 ce.ssion of brightness, would sooner or later be destroyed. But 

 the tendency in the males to continue for an indefinite period 

 transmitting to their female offspring their own brightness, 

 would have to be eliminated by a change in the form of in- 

 heritance; and this, as shewn by our previous illustration, 

 would be extremely difficult. The more probable result of the 

 long-continued destruction of the more brightly-coloured females, 

 sujiposing the equal form of transmission to prevail, would be 

 the lessening or annihilation of the bright colours of the males, 

 owing to their continual crossing with the duller females. It 

 would be tedious to follow out all the other possible results; 

 but I may remind the reader that if sexually-limited variations 

 in brightness occurred in the females, even if they were not in 

 the least injurious to them and consequently were not elimi- 

 nated, yet they would not be favoured or selected, for the male 

 usually accepts any female, and does not select the more at- 

 tractive individuals ; consequently these variations would be 

 liable to be lost, and would have little influence on the character 

 of the race ; and this will aid in accounting for the females being 

 jommonly duller-coloured than the males. 



In the eighth chapter instances were given, to which many 

 might nere be added, of variations occurring at various ages, and 

 inherited at the corresponding age. It was also shewn that va- 

 riations which occur late in life are commonly transmitted to the 

 same sex in which they first appear; whilst variations odfcurrinjl 



