354 DARWINISM TO-DAY. 



Cunningham 31 (and also at about the same time Wigles- 

 worth) in 1898 suggested, on a neo-Lamarckian basis, that 

 secondary sexual characters were due to the 

 stimulation of parts through use or external 



secondary sexual violence or irritation. Cunningham would ex- 

 characters, . . . . 



plain all adaptations as derived from variations 



actually induced by responses or reactions to the environ- 

 ment. His theory of the origin of secondary sexual char- 

 acters would simply be the explanation of the adaptive dif- 

 ferences between two individuals of a species on the same 

 basis as the explanation of the adaptive differences between 

 individuals of different species. His argument is summed 

 up as follows : "Selection assumes the occurrence of varia- 

 tions ; the variations must either be similarly indefinite and 

 promiscuous in all cases, or they must be different in differ- 

 ent cases that is, in different species, different sexes, dif- 

 ferent stages of life. If they are different in different cases, 

 then selection is a very unimportant matter, for the chief 

 questions are evidently what are the differences and what 

 made them differ. To deny that the variations have always 

 been different in different cases is to deny the most evident 

 facts ; such denial might be possible when we consider only 

 the difference between species, but it is impossible when 

 we study the differences between the sexes in the same 

 species and between different stages in the same individual. 

 In all cases the variations correspond to differences in habits 

 and mode of life, and in many cases are of the same kind 

 as the changes known to be produced in the individual by 

 special stimulation or special activity of organs ; this is true 

 of many and probably of all cases of adaptation. The gen- 

 eral conclusion is that adaptation is not produced indirectly 

 by the selection from indefinite variations, but directly by the 

 influence of stimulation in modifying the growth of the 

 parts or organs of the body." 



Wallace 32 has suggested that the differences in color- 



