progress of nations toward
a correspondence with the conditions to which they are exposed.

To the same conclusion also must he be brought who advocates the origin
of different races from different centres. It comes to the same thing,
whichever of those doctrines we adopt. Each brings us to the admission
of the transitory nature of typical forms, to their transmutations and
extinctions.

[Sidenote: Human variations.]

Variations in the aspect of men are best seen when an examination is
made of nations arranged in a northerly and southerly direction; the
result is such as would ensue to an emigrant passing slowly along a
meridional track; but the case would be quite different if the movement
were along a parallel of latitude. In this latter direction the
variations of climate are far less marked, and depend much more on
geographical than on astronomical causes. In emigrations of this kind
there is never that rapid change of aspect, complexion, and intellectual
power which must occur in the other. Thus, though the mean temperature
of Europe increases from Poland to France, chiefly through the influence
of the great Atlantic current transferring heat from the Gulf of Mexico
and tropical ocean, that rise is far less than would be encountered on
passing through the same distance to the south. By the arts of
civilization man can much more easily avoid the difficulties arising
from variations along a parallel of latitude than those upon a meridian,
for the simple reason that in that case those variations are less.

[Sidenote: Their political result.]

But it is not only complexion, development of the brain, and, therefore,
intellectual power, which are thus affected. With difference of climate
there must be differences of manners and customs, that is, differences
in the modes of civilization. These are facts which deserve our most
serious attention, since such differences are inevitably connected with
political results. If homogeneousness be an element of strength, an
empire that lies east and west must be more powerful than one that lies
north and south. I cannot but think that this was no inconsiderable
cause of the greatness and permanence of Rome and that it lightened the
task of the emperors, often hard enough, in government. There is a
natural tendency to homogeneousness in the east and west direction, a
tendency to diversity and antagonism in the north and south, and hence
it is that government under the latter ci