rrestrial globe remains in the same state. Everything, after a
while, undergoes different changes, more or less prompt, according
to the nature of the objects and of circumstances. Elevated areas
are constantly being lowered, and the loose material carried down to
the lowlands. The beds of rivers, of streams, of even the sea, are
gradually removed and changed, as also the climate;[167] in a word,
the whole surface of the earth gradually undergoes a change in
situation, form, nature, and aspect. We see on every hand what
ascertained facts prove; it is only necessary to observe and to give
one's attention to be convinced of it.

"However, if, relatively to living beings, the diversity 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
organization and its form.

"All the modifications that each living being will have undergone as
the result of change of circumstances which have influenced its
nature will doubtless be propagated by heredity (_generation_). 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 structure and its form.

"I very well know that to our eyes there seems in this respect a
_stability_ which we believe to be constant, 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
(_Phoenicopterus_) 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 history has been transmitted for 2,000 or 3,000
years are always the same, and have lost or acquired nothing in the
process of perfection of their organs and in the form of their
different parts. We may be assured 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 to the