HOW IS ORGANIC EVOLUTION CAUSED? 407 



type which exists among animals, he regards their devia- 

 tions from one another, as caused by differences in their 

 modes of life : such deviations being directly adaptive. 

 Enumerating various appliances for procuring food, he says 

 they all " seem to have been gradually produced during many 

 generations by the perpetual endeavour of the creatures to 

 supply the want of food, and to have been delivered to their 

 posterity with constant improvement of them for the pur- 

 poses required." And the creatures possessing these va- 

 rious appliances, are considered as having been rendered 

 unlike, by seeking for food in unlike ways. As illustrating 

 the alterations wrought by changed circumstances, he names 

 the acquired characters of domestic animals. La- 



marck has elaborated the same view in detail : using for the 

 purpose, with great ingenuity, his extensive knowledge of 

 the animal kingdom. From a passage in the Avertissement, 

 it would at first sight seem, that he looks upon direct adapt- 

 ation to new conditions, as the chief cause of evolution. He 

 says "Je regardai comme certain que le mouvement des 

 fluides dans 1'interieur des animaux, mouvement qui c'est 

 progressivement accelere avec la composition plus grande de 

 1'organisation ; et que Vinfluence des circonstances nouvelles, 

 a mesure que les animaux s'y exposerent en se repandant 

 dans tous les lieux habitables, furent les deux causes ge'ne'- 

 rales qui ont amene les differens animaux a 1'etat ou nous les 

 voyons actuellement." But elsewhere, the view he expresses 

 appears decidedly different from this. He asserts that "dans 

 sa marche, la nature a commence, et recommence encore tous 

 les jours, par former les corps organises les plus simples ; " 

 and that " les premieres ebauches de I'animal et du vegetal 

 tant formees dans les lieux et les circonstances conveiiables, 

 les facultes d'une vie commencante et d'un mouvement or- 

 ganique etabli, ont necessairement developpe peu a peu les 

 organes, et qu'avec le temps elles les ont diversifies ainsi que 

 les parties." And then, further on, he puts in italics this 

 proposition : " La progression dans la composition de for- 



