RESUME 333 



in the influence exerted upon the physiology of the 

 organism by the various external factors. 



As soon as we consider external factors we leave 

 the domain of adaptive phenomena. We fail to see 

 how factors like climate, temperature or nutrition 

 could, by exerting their influence upon an animal or a 

 plant, bring about such modifications as would facili- 

 tate the animal's or the plant's existence under given 

 conditions. Cold may deepen the colouration of but- 

 terfly's wings and heat may increase the pigmentation 

 of the human skin, but we fail to detect any useful- 

 ness in such changes. Those modifications may be 

 useful in certain cases: when cold causes hair or 

 feathers to turn white it may render a service to the 

 animals inhabiting the Polar regions by enabling 

 them to escape detection; but this is a pure coinci- 

 dence from which we can draw no conclusion. 



The influence of non-adaptive factors is the more 

 far reaching as those factors, being dependent upon 

 conditions of life which are common to a large num- 

 ber of individuals, bring about general variations 

 which do not dwindle away as individual variations do. 

 A general variation cannot become a factor in the 

 transformation of species unless it be inherited; and 

 it is precisely in variations of this kind that we find 

 the most convincing evidence as to the transmission of 

 acquired characters and it is to them that our tenta- 



