442 THE DESCENT OF MAN. 



and complex, perhaps an Impossible process, to change one form 

 of transmission into the other through selection. Therefore, 

 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 first 

 sexually limited in their transmission, there would not be the 

 least difficulty in rendering a male bird widely different in color 

 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 colors are of service to the males in their rivalry 

 with other males, such colors would be selected, whether or not 

 they were transmitted exclusively to the same sex. Consequently 

 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 colors were of high importance for the safety of 

 the female during incubation, as with many ground birds, the 

 females which varied in brightness, or which received through 

 inheritance from the males any marked accession 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 elim- 

 inated by a change in the form of inheritance; and this, as shown 

 by our previous illustration, would be extremely difficult. The 

 more probable result of the long-continued destruction of the 

 more brightly-colored females, supposing the equal form of trans- 

 mission to prevail, would be the lessening or annihilation of the 

 bright colors 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 sex- 

 ually-limited variations in brightness occurred in the females, 

 even if they were not in the least injurious to them and conse- 

 quently were not eliminated, yet they v/ould not be favored or 

 selected, for the male usually accepts any female, and does not 

 select the more attractive individuals; consequently these varia- 

 tions 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 commonly duller-colored than the males. 



In the eighth chapter instances were given, to which many 

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

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

 riations which occur late in life are commonly transmitted to the 

 same sex in v/hich they first appear; whilst variations occurring 

 early in life are apt to be transmitted to both sexes; not that all 



