202 ORGANIC EVOLUTION CONSIDERED 



Male spiders are smaller than the females, a fact 

 which natural selection cannot explain, for I know 

 of no advantage that would be gained by the decrease, 

 sometimes very great, in the size of the males, and 

 it is simply an assumption to claim that sexual selec- 

 tion has produced the difference in size. 



With regard to fishes, both sexes of which are 

 highly colored, Mr. Darwin says: " On the whole, 

 the most probable view in regard to the fishes," of 

 which both sexes are brilliantly colored, is that their 

 colors have been acquired by the males as a sexual 

 ornament, and have been transferred in an equal or 

 nearly equal degree to the other sex."* 



He admits that brilliantly colored fishes would be 

 more exposed to danger from enemies, and that, con- 

 sequently, their colors could not have been developed 

 by natural selection. He therefore adopts the theory 

 of sexual selection which he supplements with the 

 theory that the ornament has been transmitted from 

 the male to the female. This theory he applies also 

 to birds t and to reptiles.! 



Again he says: "With the species in which the 

 sexes differ in color, it is possible that at first there 

 existed a tendency to transmit the successive varia- 

 tions equally to both sexes; and that the females were 

 prevented from acquiring the bright colors of the 

 males, on account of the danger to which they would 

 have been exposed during incubation." § 



Yet there are many instances in which the females 

 are brilliantly colored, and others in which the highly 

 ornamented males incubate the eggs. 



To try to account for the many differences of color, 

 etc., between the sexes is quite bewildering. To each 

 theory offered there are so many exceptions that they 



* Descent of Man, Vol. 2, p. 17. t Ibid, Vol. 2, p. 163. 

 % Ibid, p. 35. § Ibid, p. 225. 



