28 THEORY OF EVOLUTION 



earth slowly changed as the carbon dioxide 

 contents in the air altered as land appeared 

 and as marine animals left the water to inhabit 

 it, they or their embryos responded to the new 

 conditions and those that responded favorably 

 gave rise to new creations. As the environ- 

 ment changed the fauna and flora changed 

 change for change. Here we have a picture of 

 progressive evolution that carries with it an 

 idea of mechanical necessity. If there is any- 

 thing mystical or even improbable in St. Hi- 

 liare's argument it does not appear on the sur- 

 face ; for he did not assume that the response to 

 the new environment was always a favorable 

 one or, as we say, an adaptation. He expressly 

 stated that if 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 exist- 

 ence in a new environment and these would 

 come to inherit the earth. In this sense he an- 

 ticipated certain phases of the natural selection 

 theory of Darwin, but only in part; for his 

 picture is not one of strife within and without 



