er
habits.

"Indeed, this can never be denied, because, in fact, nature on a
thousand other occasions shows us, in the power exercised by
circumstances on habits, and in that of the influence of habits on
forms, dispositions, and the proportion of the parts of animals,
truly analogous facts.

"A great number of citations being unnecessary, we now see to what
the case under discussion is reduced.

"The fact is that divers animals have each, according to their genus
and their species, special habits, and in all cases an organization
which is perfectly adapted to these habits.

"From the consideration of this fact, it appears that we should be
free to admit either one or the other of the following conclusions,
and that only one of them is susceptible of proof.

"_Conclusion admitted up to this day_: Nature (or its Author), in
creating the animals, has foreseen all the possible kinds of
circumstances in which they should live, and has given to each
species an unchanging organization, as also a form determinate and
invariable in its different parts, which compels each species to
live in the places and in the climate where we find it, and has
there preserved its known habits.

"_My own conclusion_: Nature, in producing in succession every
species of animal, and beginning with the least perfect or the
simplest to end her work with the most perfect, has gradually
complicated their structure; and these animals spreading generally
throughout all the inhabitable regions of the globe, each species
has received, through the influence of circumstances to which it has
been exposed, the habits which we have observed, and the
modifications in its organs which observation has shown us it
possesses.

"The first of these two conclusions is that believed up to the
present day--namely, that held by nearly every one; it implies, in
each animal, an unchanging organization and parts which have never
varied, and which will never vary; it implies also that the
circumstances of the places which each species of animal inhabits
will never vary in these localities; for should they vary, the same
animals could not live there, and the possibility of discovering
similar forms elsewhere, and of transporting them there, would be
forbidden.

"The second conclusion is my own: it implies that, owing to the
influence of circumstances on habits, and as the result of t