122 BIOLOGY AND SOCIAL PROBLEMS 



the black and white guinea-pigs already al- 

 luded to, we may have two individuals with 

 indistinguishable exteriors and yet with very 

 different germinal possibilities. One stock of 

 black guinea-pigs, depending upon its ances- 

 try, is able to produce nothing but black de- 

 scendants, and another stock of black indi- 

 viduals, indistinguishable externally from the 

 first but differing from it in its ancestry, can 

 bring forth white offspring as well as black. 

 In the preservation of black individuals, nat- 

 ural selection would act the same in the two 

 stocks, but one stock would be more effective 

 than the other in establishing a black race. 

 Thus germinal composition may be a factor of 

 no small importance in limiting the effective- 

 ness of natural selection, a process which is 

 of undoubted significance in nature, but which 

 may be much more restricted in its applica- 

 tion and effectiveness than its advocates have 

 suspected. 



That natural selection influences man as it 

 does other organisms is an undoubted fact. 

 Every epidemic that carries off human beings 

 acts selectively, and if it affects individuals in 

 early life and before the period of reproduc- 

 tive activity, it may have great importance 



