LAMARCK’S THEORY OF DESCENT ‘201 
there are many others which, in addition, have a con- 
siderable influence in the production of the effects in 
question. 
“Tt is known that different localities 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, these 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 speczes. 
“Tt 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. 
“Tn 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 noticethem. He is obliged to consult monu- 
