to acquire it by the
means which have in reality created it.

"Besides, in reproductive unions the crossings between the
individuals which have different qualities or forms are necessarily
opposed to the continuous propagation of these qualities and these
forms. We see that in man, who is exposed to so many diverse
circumstances which exert an influence on him, the qualities or the
accidental defects which he has been in the way of acquiring, are
thus prevented from being preserved and propagated by generation.
If, when some particular features of form or any defects are
acquired, two individuals under this condition should always pair,
they would reproduce the same features, and the successive
generations being confined to such unions, a special and distinct
race would then be formed. But perpetual unions between individuals
which do not have the same peculiarities of form would cause all the
characteristics acquired by special circumstances to disappear.

"From this we can feel sure that if distances of habitation did not
separate men the intermixture by generation would cause the general
characteristics which distinguish the different nations to
disappear.

"If I should choose to pass in review all the classes, all the
orders, all the genera, and all the species of animals which exist,
I should show that the structure of individuals and their parts,
their organs, their faculties, etc., etc., are in all cases the sole
result of the circumstances in which each species is found to be
subjected by nature and by the habits which the individuals which
compose it have been obliged to contract, and which are only the
product of a power primitively existing, which has forced the
animals into their well-known habits.

"We know that the animal called the _ai_, or the sloth (_Bradypus
tridactylus_), is throughout life in a condition so very feeble that
it is very slow and limited in its movements, and that it walks on
the ground with much difficulty. Its movements are so slow that it
is thought that it cannot walk more than fifty steps in a day. It is
also known that the structure of this animal is in direct relation
with its feeble state or its inaptitude for walking; and that should
it desire to make any other movements than those which it is seen to
make, it could not do it.

"Therefore, supposing that this animal had received from nature its