he fortieth
parallel in America soon exterminates the negroes.[50]

The Indians of South America, though all fundamentally of the same
ethnic stock, are variously acclimated to the warm, damp, forested
plains of the Amazon; to the hot, dry, treeless coasts of Peru; and to
the cold, arid heights of the Andes. The habitat that bred them tends to
hold them, by restricting the range of climate which they can endure. In
the zone of the Andean slope lying between 4,000 and 6,000 feet of
altitude, which produces the best flavored coffee and which must be
cultivated, the imported Indians from the high plateaus and from the low
Amazon plains alike sicken and die after a short time; so that they take
employment on these coffee plantations for only three or five months,
and then return to their own homes. Labor becomes nomadic on these
slopes, and in the intervals these farm lands of intensive agriculture
show the anomaly of a sparse population only of resident managers.[51]
Similarly in the high, dry Himalayan valley of the upper Indus, over
10,000 feet above sea level, the natives of Ladak are restricted to a
habitat that yields them little margin of food for natural growth of
population but forbids them to emigrate in search of more,--applies at
the same time the lash to drive and the leash to hold, for these
highlanders soon die when they reach the plains.[52] Here are two
antagonistic geographic influences at work from the same environment,
one physical and the other social-economic. The Ladaki have reached an
interesting resolution of these two forces by the institution of
polyandry, which keeps population practically stationary.

[Sidenote: Pigmentation and climate.]

The relation of pigmentation to climate has long interested geographers
as a question of environment; but their speculations on the subject have
been barren, because the preliminary investigations of the physiologist,
physicist and chemist are still incomplete. The general fact of
increasing nigrescence from temperate towards equatorial regions is
conspicuous enough, despite some irregularity of the shading.[53] This
fact points strongly to some direct relation between climate and
pigmentation, but gives no hint how the pigmental processes are
affected. The physiologist finds that in the case of the negro, the dark
skin is associated with a dense cuticle, diminished perspiration,
smaller chests and less respiratory power, a lower temperature and more
rapid