296 THE DESCENT OF MAN 



ing his voice, pouring out odoriferous secretions, etc. ; and 

 this expenditure is generally concentrated within a short 

 period. The great vigor of the male during the season 

 of love seems often to intensify his colors, independently of 

 any marked difference from the female."' In mankind, and 

 even as low down in the 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 accumulated and increased 

 by sexual or natural selection. Nevertheless, they may 

 become permanent if the exciting cause acts permanently; 

 and, in accordance with a frequent form of inheritance, 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 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, etc., between the two re- 

 gions. Now, in some few cases, the two sexes of the same 

 species appear to have been differently affected; in the 



2' Prof. Mantegazza is inclined to believe ("Lettera a Carlo Darwin," 

 "Archivio per 1' Anthropologia, " 18tl, p. 306) that the bright colors common 

 in so many male animals are due to the presence and retention 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. 



'" Eor mankind, see Dr. J. Stockton-Hough, whose conclusions are given in 

 the "Pop. Science Review," 18'74, p. 97. See Girard's observations on ths 

 Lepidoptera, as given in the "Zoological Record," 1869, p. 341, 



