Darwin s Theory of Sexual Selection 173 



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." 



Again: "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 in- 

 creased by sexual or natural selection. Nevertheless, they 

 may become permanent if the exciting cause acts perma- 

 nently ; 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 

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

 species appear to have been differently affected ; in the 

 Agel(B7is phceniceus the males have had their colors greatly 

 intensified in the south ; whereas with Cardinalis virginianus 

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

 calus major the females have been rendered extremely vari- 

 able in tint, whilst the males remain nearly uniform." 



The admissions contained in this statement would seem 

 to jeopardize the entire question, for, if it is admitted that, on 

 account of the difference in the constitution of the two sexes, 

 the influence of the surrounding conditions would produce a 

 different effect on them, it would seem that there is no need 

 whatsoever for the theory of sexual selection. What Darwin 



