Anglo-American has ceased to resemble his ancestors in physical
appearance. Alterations have taken place in the skin, the hair, the
neck, and the head; the lower jaw has become bigger; the bones of the
arms and legs have lengthened, and the American of to-day requires a
different kind of glove from the Englishman. Structural changes of a
similar character have taken place in the negroes transplanted to
America. M. Elisée Reclus considers that in a century and a half they
have traversed a good quarter of the distance which separates them from
the whites. Another important point, as showing the influence of
habitat upon race, is the fact that the modifications of human
structure resulting from residence in America are in the direction of
assimilating the European type to that of the red man.[11] In short, it
may be taken as a well-established principle that external nature
destroys all organisms that cannot adapt themselves to its action, and
physiologically modifies all organisms that can.

[11] The various types of Jews also afford a striking instance of
the effect of natural surroundings on bodily structure.

The social condition of mankind is also profoundly affected by climatic
and other external circumstances. The intense cold of the Arctic and
Antarctic regions is fatal to anything approaching a developed form of
civilisation. Intense heat, on the other hand, although not
incompatible with a certain degree of progress, is unfavourable to its
permanence;[12] the extinct societies of the tropics, such as Cambodia,
Mexico and Peru, affording instances of the operation of this law. It
is impossible for man to get beyond the nomad state in the vast deserts
of Northern Africa; and the extreme moisture of the atmosphere in other
portions of the same continent puts an effectual check on anything like
social advance. In some parts of the world social development has been