220 THE DESCENT OF MAN. 



organic scale as in the Lepidoptera, the temperature of the body 

 is higher in the male than in the female, accompanied in the case 

 of man by a slower pulse."" On the whole the expenditure of 

 matter and force by the two sexes is probably nearly equal, though 

 effected in very different ways and at different rates. 



From the causes just specified the two sexes can hardly fail to 

 differ somewhat in constitution, at least during the breeding 

 season: and, although they may be subjected to exactly the same 

 conditions, they will tend to vary in a different manner. If such 

 variations are of no service to either sex, they will not be accu- 

 mulated and increased by sexual or natural selection. Neverthe- 

 less, they may become permanent if the exciting cause acts per- 

 manently; and in accordance with a frequent form of inheritance 

 fhey may be transmitted to that sex alone in which they first 

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

 nent, yet unimportant, differences of character. For instance, 

 Mr. Allen shows that with a large number of birds inhabiting the 

 northern and southern United States, the specimens from the 

 south are darker-colored 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 af- 

 fected; in the Agelaeus phoBniceus the males have had their colors 

 greatly intensified in the south; whereas with Cardinalis virgin- 

 ianus it is the females which have been thus affected; with Quis- 

 calus major the females have been rendered extremely variable in 

 tint, whilst the males remain nearly uniform.'' 



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

 which the females instead of the males have acquired well pro- 

 nounced secondary sexual characters, such as brighter colors, 

 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 ap- 

 parently selecting the more attractive females, as we may infer 

 from the results. Certain hen birds have thus been rendered 

 more highly colored or otherwise ornamented, as well as more 



common in so many male animals, are due to the presence and re- 

 tention by them of the spermatic fluid; but this can hardly be the 

 case; for many male birds, for instance young pheasants, become 

 brightly colored in the autumn of their first year. 



™ For mankind, see Dr. J. Stockton Hough, whose conclusions are 

 given in the 'Pop. Science Review,' 1874, p. 97. See Girard's observa- 

 tions on the Lepidoptera, as given in the 'Zoological Record,' 1869, p. 

 347. 



" 'Mammals and Birds of B. Florida,' pp. 234, 280, 295. 



