523 



Even if we consider somewhat more marked sexual differ- 

 ences, is it probable, for instance, that the head of the 

 female chaffinch, the crimson on the breast of the female 

 bullfinch, the green of the female greenfinch, the crest of 

 the female golden-crested wren have all been rendered less 

 bright by the slow process of selection for the sake of pro- 

 tection ? I cannot think so; and still less with the slight 

 differences between the sexes of those birds which buiid 

 concealed nests. On the other hand, the differences in 

 color between the sexes, whether great or small, may to a 

 large extent be explained on the principle of the successive 

 variations acquired by the males through sexual selection, 

 having been from the first more or less limited in their 

 transmission to the females. That the degree of limitation 

 should differ in different species of the same group will not 

 surprise any one who has studied the laws of inheritance, 

 for they are so complex that they appear to us in our igno- 

 rance to be capricious in their actions.* 



As far as I can discover there are few large groups of 

 birds in which all the species have both sexes alike and 

 brilliantly colored, but I hear from Mr. Sclater that this 

 appears to be the case with the Musophagae or plantain- 

 eaters. Nor do I believe that any large group exists in 

 which the sexes of all the species are widely dissimilar in 

 color. Mr. Wallace informs me that the chatterers of 

 South America ( Cotingidce) offer one of the best instances; 

 but with some of the species in which the male has a splen- 

 did red breast the female exhibits some red on her breast; 

 and the females of other species show traces of the green 

 and other colors of the males. Nevertheless we have a 

 near approach to close sexual similarity or dissimilarity 

 throughout several groups; and this, from what has just 

 been said of the fluctuating nature of inheritance, is a 

 somewhat surprising circumstance. But that the same 

 laws should largely prevail with allied animals is not sur- 

 prising. The domestic fowl has produced a great number 

 of breeds and sub-breeds, and in these the sexes generally 

 differ in plumage; so that it has been noticed as an un- 

 usual circumstance when in certain sub -breeds they 

 resemble each other. On the other hand, the domestic 



*See remarks to this effect in my work on "Variation under 

 Domestication," vol. ii, chap. xii. 



