The Evidence from Sexual Characters. 241 



is certainly no difficulty in believing that these instincts 

 have had a male origin. 



The remarkable instinct which leads some species of 

 cuckoo and crow blackbirds to lay their eggs in the nests 

 of other species, must have originated in females, and a 

 collection of all the cases which must be explained in 

 the same way would make a formidable list, but the fact 

 would still remain true, that among animals with separate 

 sexes, male modifications are very much more frequent 

 than female modifications, and this is all that our the- 

 ory requires. 



