CHAPTEE VI 



ETIENNE GEOFFROY-SAINT-HILAIRE 



Direct action of the environment Hypothesis of sudden variations 

 Phenomena of arrested development. 



LIKE his colleague at the Jardin des Plantes, Etienne 

 Geoffroy-Saint-Hilaire was a convinced transformist. 

 As regards the mechanism of evolution it may be 

 said that his ideas only differ from those of Lamarck 

 by a few tones. Like Lamarck, he admits the unity 

 of a pre-established plan, the realization of which 

 takes place partly under the influence of wants and 

 habits, but still more under the direct action of the 

 surroundings, among which Geoffrey considers as 

 the most important : the cooling of the earth, and 

 still more the gradual diminution of the quantity 

 of oxygen contained in the air. Thence comes the 

 preponderating influence which this scholar is led to 

 attribute to modifications of the act of respiration. 

 But Geoffroy-Saint-Hilaire remained, even more 

 than Lamarck, a stranger to palaeontology, and to 

 the real genealogical history of living beings, a fact 

 which prevents us from dwelling much on his works. 

 On the other hand it is interesting to point 'out in 

 his work two ideas personal to himself, and both 

 destined to be developed later in the history of the 

 transformist doctrines. There are, first, the hypo- 

 thesis of sudden variations, substituted for that of 

 D 33 



