Chap. YI11. Sexual Selection. 225 



permanently ; and in accordance with a frequent form of inheri- 

 tance they may be transmitted to that sex alone in which they 

 first appeared. In this case the two sexes will come to present 

 permanent, yet unimportant, differences of character. For 

 instance, Mr. Allen shews that with a large number of bird3 

 inhabiting the northern and southern United States, the speci- 

 mens from the south are darker-coloured than those from the 

 north ; and this seems to be the direct result of the difference in 

 temperature, light, &c, between the two regions. Now, in some 

 few cases, the two sexes of the same species appear to have been 

 differently affected ; in the Agelceus phmriceus the males have had 

 their colours greatly intensified in the south ; whereas with Car- 

 dinalis virgin ianus it is the females which have been thus affected ; 

 with Quiscalus major the females have been rendered extremely 

 variable in tint, whilst the males remain nearly uniform. 31 



A few exceptional cases occur in various classes of animals, in 

 which the females instead of the males have acquired well 

 pronounced secondary sexual characters, such as brighter colours, 

 greater size, strength, or pugnacity. With birds there has some- 

 times been a complete transposition of the ordinary characters 

 proper to each sex ; the females having become the more eager 

 in courtship, the males remaining comparatively passive, but 

 apparently selecting the more attractive females, as we may infer 

 from the results. Certain hen birds have thus been rendered 

 more highly coloured or otherwise ornamented, as well as more 

 powerful and pugnacious than the cocks ; these characters being 

 transmitted to the female offspring alone. 



It may be suggested that in some cases a double process of 

 selection has been carried on ; that the males have selected 

 the more attractive females, and the latter the more attractive 

 males. This process, however, though it might lead to the 

 modification of both sexes, would not make the one sex 

 different from the other, unless indeed their tastes for the beauti- 

 ful differed ; but this is a supposition too improbable to be worth 

 considering in the case of any animal, excepting man. There 

 are, however, many animals in which the sexes resemble each 

 other, both being furnished with the same ornaments, which 

 analogy would lead us to attribute to the agency of sexual 

 selection. In such cases it may be suggested with more plausi- 

 bility, that there has been a double or mutual process of sexual 

 selection ; the more vigorous and precocious females selecting 

 the more attractive and vigorous males, the latter rejecting all 

 except tho more attractive females. But from what we know 



« ' Mammals and Birds of E. Florida,' pp. 234, 280, 295. 

 11 



