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 pulse,[54] all which variations may enter into the problem of the
negroes coloring. The question is therefore by no means simple.

Yet it is generally conceded by scientists that pigment is a protective
device of nature. The negro's skin is comparatively insensitive to a sun
heat that blisters a white man. Livingstone found the bodies of albino
negroes in Bechuana Land always blistered on exposure to the sun,[55]
and a like effect has been observed among albino Polynesians, and
Melanesians of Fiji.[56] Paul Ehrenreich finds that the degree of
coloration depends less upon annual temperature than upon the direct
effect of the sun's rays; and that therefore a people dwelling in a
cool, dry climate, but exposed to the sun may be darker than another in
a hot, moist climate but living in a dense forest. The forest-dwelling