8 EVOLUTION AND GENETICS 



gressive evolution that carries with it an idea of 

 mechanical necessity. If there is anything mystical 

 or even improbable in St. Hilaire's argument it does 

 not appear on the surface ; for he did not assume that 

 the response to the new environment was always a 

 favorable one or, as we say, an adaptation. He ex- 

 2)ressly stated that // the response was unfavorable 

 the individual or the race died out. He assumed that 

 sometimes the change might be favorable, i.e., that 

 certain species, entire groups, would respond in a 

 direction favorable to their existence in a new envi- 

 ronment and these would come to inherit the earth. 

 In this sense he anticipated certain phases of the 

 natural selection theory of Darwin, but only in part ; 

 for his picture is not one of strife within and without 

 the species, but rather the escape of the species from 

 the old into a new world. 



If, then, we recognize the intimate bond in chem- 

 ical constitution of living things and of the world in 

 which they develop, what is there improbable in St. 

 Hilaire's hypothesis? Why, in a word, is not more 

 credit given to St. Hilaire in modern evolutionary 

 thought ? The reasons are to be found, I think, first, 

 in that the evidence to which he appealed was meagre 

 and inconclusive; and, second, in that much of his 

 special evidence does not seem to us to be applicable. 

 For example the monstrous forms that development 

 often assumes in a strange environment, and with 

 which every embryologist is only too familiar, rarely 



