Chap. VIII.] SEXUAL SELECTION. 267 



that variations in the muscles " are probably more com- 

 mon in males than females." Certain muscles which are 

 not normally present in mankind are also more frequently 

 developed in the male than in the female sex, although 

 exceptions to this rule are said to occur. Dr. Burt Wild- 

 er 18 has tabulated the cases of 152 individuals with su- 

 pernumerary digits, of which 86 were males, and 39, or less 

 than half, females ; the remaining 27 being of unknown 

 sex. It should not, however, be overlooked that women 

 would more frequently endeavor to conceal a deformity 

 of this kind than men. Whether the large proportional 

 number of deaths of the male offspring of man and appar- 

 ently of sheep, compared with the female offspring, be- 

 fore, during, and shortly after birth (see supplement), has 

 any relation to a stronger tendency in the organs of the 

 male to vary and thus to become abnormal in structure or 

 function, I will not pretend to conjecture. 



In various classes of animals a few exceptional cases 

 occur, in which the female instead of the male has ac- 

 quired well-pronounced secondary sexual characters, such 

 as brighter colors, greater size, strength, or pugnacity. 

 With birds, as we shall hereafter see, there has sometimes 

 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, as we may infer from 

 the results, the more attractive females. Certain female 

 birds have thus been rendered more highly colored or 

 otherwise ornamented, as well as more powerful and pug- 

 nacious, than the males, these characters being transmit- 

 ted to the female offspring alone. 



It may be suggested that in some cases a double pro- 

 cess .of selection has been carried on ; the males having 



18 'Massachusetts Medical Soc' vol. ii. No. 3, 1868, p. 9. 



