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 as in Piedmont and Lombardy in the north.[63] The dark Hamitic Berbers of northern Africa have developed an unmistakable blond variant in high valleys of the Atlas range, which in a sub-tropical region rises to the height of 12,000 feet.  Here among the Kabyles the population is fair; grey, blue or green eyes are frequent, as is also reddish blond or chestnut hair.[64] Waitz long ago affirmed this tendency of mountaineers to lighter coloring from his study of primitive peoples.[65] The modification can not be attributed wholly to climatic contrast between mountain and plain.  Some other factor, like the economic poverty of the environment and the poor food-supply, as Livi suggests, has had a hand in the result; but just what it is or how it has operated cannot yet be defined.[66]

[Sidenote:  Difficulty of Generalization]

Enough has been said to show that the geographer can formulate no broad generalization as to the relation of pigmentation and climate from the occurrence of the darkest skins in the Tropics; because this fact is weakened by the appearance also of lighter tints in the hottest districts, and of darker ones in arctic and temperate regions.  The geographer must investigate the questions when and where deeper shades develop in the skins of fair races; what is the significance of dark skins in the cold zones and of fair ones in hot zones.  His answer must be based largely on the conclusions of physiologists and physicists, and only when these have reached a satisfactory solution of each detail of the problem can the geographer summarize the influence of environment upon pigmentation.  The rule can therefore safely be laid down that in all investigation of geographic influences upon the permanent physical characteristics of races, the geographic distribution of these should be left out of consideration till the last, since it so easily misleads.[67] Moreover, owing to the ceaseless movements of mankind, these effects do not remain confined to the region that produced them, but pass on with the wandering throng in whom they have once developed, and in whom they endure or vanish according as they prove beneficial or deleterious in the new habitat.

[Sidenote:  Psychical effects.]