250 LAMARCK, HIS LIFE AND WORK 



sity of circumstances brings about for them a diversity 

 of habits, a different mode of existence, and, as the 

 result, modifications in their organs and in the shape 

 of their parts, one should believe that very gradually 

 every living body whatever would vary in its organi- 

 ization and its form. 



I " All the modifications that each living being will 

 [have undergone as the result of change of circum- 

 \ stances which have influenced its nature will doubt- 

 ' less be propagated by heredity {gdn^ratioti). But as 

 new modifications will necessarily continue to operate, 

 however slowly, not only will there continually be 

 found new species, new genera, and even new orders, 

 but each species will vary in some part of its struc- 

 ture and its form. 



" I very well know that to our eyes there seems in 

 this respect a stability which we believe to be con- 

 stant, although it is not so truly ; for a very great 

 number of centuries may form a period insufficient 

 for the changes of which I speak to be marked enough 

 for us to appreciate them. Thus we say that the 

 flamingo {Phcenicopterus) has always had as long legs 

 and as long a neck as have those with which we are 

 familiar; finally, it is said that all animals whose his- 

 tory has been transmitted for 2,000 or 3,000 years 

 are always the same, and have lost or acquired noth- 

 ing in the process of perfection of their organs and 

 in the form of their different parts. We may be as- 

 sured that this appearance of stability of things in 

 nature will always be taken for reality by the average 

 of mankind, because in general it judges everything 

 only relatively to itself. 



" But, I repeat, this consideration which has given 

 rise to the admitted error owes its source io the very 

 great slowness of the changes which have gone on. A 

 little attention given to the facts which I am about 

 to cite will afford the strongest proof of my assertion. 



" What nature does after a great length of time we 



