Botokudos of the upper San Francisco River in Brazil are fairer than the
kindred Kayapo tribe, who inhabit the open campos; and the Arawak of the
Purus River forests are lighter than their fellows in the central Matto
Grosso.[57] Sea-faring coast folk, who are constantly exposed to the
sun, especially in the Tropics, show a deeper pigmentation than their
kindred of the wooded interior.[58] The coast Moros of western Mindanao
are darker than the Subanos, their Malay brethren of the back country,
the lightness of whose color can be explained by their forest life.[59]
So the Duallas of the Kamerun coast of Africa are darker than the
Bakwiri inhabiting the forested mountains just behind them, though both
tribes belong to the Bantu group of people.[60] Here light, in
contradistinction to heat, appears the dominant factor in pigmentation.
A recent theory, advanced by von Schmaedel in 1895, rests upon the
chemical power of light. It holds that the black pigment renders the
negro skin insensitive to the luminous or actinic effects of solar
radiation, which are far more destructive to living protoplasm than the
merely calorific effects.[61]

[Sidenote: Pigmentation and altitude]

Coloration responds to other more obscure influences of environment. A
close connection between pigmentation and elevation above sea level has
been established: a high altitude operates like a high latitude.
Blondness increases appreciably on the higher slopes of the Black
Forest, Vosges Mountains, and Swiss Alps, though these isolated
highlands are the stronghold of the brunette Alpine race.[62] Livi, in
his treatise on military anthropometry, deduced a special action of
mountains upon pigmentation on observing a prevailing increase of
blondness in Italy above the four-hundred meter line, a phenomenon which
came out as strongly in Basilicata and Calabria provinces of the south