LAMARCK'S THEORY OF DESCENT 30I 



there are many others which, in addition, have a con- 

 siderable influence in the production of the effects in 

 question. 



" It is known that different locahties change in na- 

 ture and quality owing to their position, their nature, 

 and their climate, as is easily seen in passing over 

 different places distinguished by special features ; 

 hence we see a cause of variation for the animals and 

 plants which live in these different places. But what 

 we do not sufficiently know, and even what we gen- 

 erally refuse to believe, is that each place itself changes 

 with time in exposure, in climate, in nature, and qual- 

 ity, although with a slowness so great in relation to 

 our own continuance that we attribute to it a perfect 

 stability. 



" Now, in either case, tliese changed localities pro- 

 portionally change the circumstances relative to the 

 organisms which inhabit them, and the latter then 

 give rise to other influences bearing on these same 

 beings. 



" We perceive from this that, if there are extremes 

 in these changes, there are also gradations — namely, 

 degrees which are intermediate and which fill the in- 

 terval. Consequently there are also gradations in the 

 differences which distinguish what we call species. 



" It is then evident that the whole surface of the 

 earth offers, in the nature and situation of the mat- 

 ters which occupy its different points, a diversity of 

 circumstances which is throughout in relation with 

 that of the forms and parts of animals, independent 

 of the special diversity which necessarily results from 

 the progress of the composition of organization in 

 each animal. 



" In each locality where animals can live, the cir- 

 cumstances which establish there an order of things 

 remain for a long time the same, and really change 

 there only with a slowness so great that man cannot 

 directly notice them. He is obHged to consult monu. 



