ess subject than any other living beings, man not
excepted, to alterations, changes, and variations of all kinds.
Being free to choose their own food and climate, they vary less than
domestic animals vary."[134]

The Buffonian factor of the direct influence of climate is not in
general of so thoroughgoing a character as usually supposed by the
commentators of Buffon. He generally applies it to the superficial
changes, such as the increase or decrease in the amount of hair, or
similar modifications not usually regarded as specific characters. The
modifications due to the direct influence of climate may be effected, he
says, within even a few generations.

Under the head of geographical distribution (in tome ix., 1761), in
which subject Buffon made his most original contribution to exact
biology, he claims to have been the first "even to have suspected" that
not a single tropical species is common to both eastern and western
continents, but that the animals common to both continents are those
adapted to a temperate or cold climate. He even anticipates the subject
of migration in past geological times by supposing that those forms
travelled from the Old World either over some land still unknown, or
"more probably" over territory which has long since been submerged.[135]

The mammoth "was certainly the greatest and strongest of all
quadrupeds, but it has disappeared; and if so, how many smaller,
feebler, and less remarkable species must have perished without
leaving us any traces or even hints of their having existed? How
many other species have changed their nature, that is to say,
become perfected or degraded, through great changes in the
distribution of land and ocean; through the cultivation or neglect
of the country which they inhabit; through the long-continued
effects of climatic changes, so that they are no longer the same
animals that they once were. Yet of all living beings after man the
quadrupeds are the ones whose nature is most fixed and form most
constant; birds and fishes vary much more easily; insects still more
again than these; and if we descend to plants, which certainly
cannot be excluded from animated nature, we shall be surprised at
the readiness with which species are seen to vary, and at the ease
with which they change their forms and adopt new natures."[136]

The following passages, debarring the error of deriving all the American
from the Old World forms,