156 



EVOLUTION AND ANIMAL LIFE 



acters": they are not to be compared with those secondary 

 sexual characters such as ornamental or aggressive spines, 

 horns, patterns, etc., which are the characteristics that give 

 males their special reputation for ultravariation. 



FIG. 95. Fore wings of honeybee (drone), showing variations in venation. 

 (After Kellogg and Bell.) 



Finally, with regard to the causal influence in variation-pro- 

 ducing of the "primary factors of evolution," such as temper- 

 ature, light, humidity, pressure, and extrinsic physicochemical 

 conditions generally, summed up commonly in the phrase 

 climate and environment, we have one all-important considera- 

 tion to keep constantly 

 in mind. However po- 

 tent and obvious the ef- 

 fects of these influences 

 are on the individual, 

 we have no proof as 

 yet of a nature to com- 

 pel the general accept- 

 ance of biologists, that 

 such effects can be car- 

 ried directly over to the 

 race or species. 



Only ten years after 

 Darwin published the 



"Origin of Species," von Kolliker, the great German zoologist, 

 in criticising the assumptions on which species-forming by 

 natural selection was based in the Darwinian theory, proposed 

 an alternative theory of heterogenesis or species-forming by 

 leaps (saltations or mutations). These saltations need not of 

 necessity to be large, but must be changes definite and fixed. 

 Later, Korschinsky, a Russian botanist, outlined in some de- 



FIG. 96. Hind wings of honeybee (drone), show- 

 ing variations in venation. Note the interpola- 

 tion of the cells. (After Kellogg and Bell.) 



