as a consequence of commerce and mutual influence, peoples do not
retain the original mental peculiarities due to climate. This may
not be true of the extreme climates in the torrid and glacial zones,
but in the temperate zone we may discount entirely climatic
influence. The climates of Greece and Italy and that of France are
too similar to cause any sensible difference between the Greeks or
Latins and the French.

Saint Sorlin and Perrault had argued directly from the permanence of
vigour in lions or trees to the permanence of vigour in man. If
trees are the same as ever, brains must also be the same. But what
about the minor premiss? Who knows that trees are precisely the
same? It is an indemonstrable assumption that oaks and beeches in
the days of Socrates and Cicero were not slightly better trees than
the oaks and beeches of to-day. Fontenelle saw the weakness of this
reasoning. He saw that it was necessary to prove that the trees, no
less than human brains, have not degenerated. But his a priori proof
is simply a statement of the Cartesian principle of the stability of
natural processes, which he put in a thoroughly unscientific form.
The stability of the laws of nature is a necessary hypothesis,
without which science would be impossible. But here it was put to an
illegitimate use. For it means that, given precisely the same
conditions, the same physical phenomena will occur. Fontenelle
therefore was bound to show that conditions had not altered in such
a way as to cause changes in the quality of nature's organic
productions. He did not do this. He did not take into consideration,
for instance, that climatic conditions may vary from age to age as
well as from country to country.

4.