Darwin holds that many slight changes in animals and plants, such as size, color, thickness of skin and hair, have been produced through food supply and climate from the external conditions under which the forms lived.[37] Paul Ehrenreich, while regarding the chief race distinctions as permanent forms, not to be explained by external conditions, nevertheless concedes the slight and slow variation of the sub-race under changing conditions of food and climate as beyond doubt.[38] Stature is partly a matter of feeding and hence of geographic condition. In mountain regions, where the food resources are scant, the varieties of wild animals are characterized by smaller size in general than are corresponding species in the lowlands. It is a noticeable fact that dwarfed horses or ponies have originated in islands, in Iceland, the Shetlands, Corsica and Sardinia. This is due either to scanty and unvaried food or to excessive inbreeding, or probably to both. The horses introduced into the Falkland Islands in 1764 have deteriorated so in size and strength in a few generations that they are in a fair way to develop a Falkland variety of pony.[39] On the other hand, Mr. Homer Davenport states that the pure-bred Arabian horses raised on his New Jersey stock farm are in the third generation a hand higher than their grandsires imported from Arabia, and of more angular build. The result is due to more abundant and nutritious food and the elimination of long desert journeys. The low stature of the natives prevailing in certain "misery spots" of Europe, as in the Auvergne Plateau of southern France, is due in part to race, in part to a disastrous artificial selection by the emigration of the taller and more robust individuals, but in considerable part to the harsh climate and starvation food-yield of that sterile soil; for the children of the region, if removed to the more fertile valleys of the Loire and Garonne, grow to average stature.[40] The effect of a scant and uncertain food supply is especially clear in savages, who have erected fewer buffers between themselves and the pressure of environment. The Bushmen of the Kalahari Desert are shorter than their Hottentot kindred who pasture their flocks and herds in the neighboring grasslands.[41] Samoyedes, Lapps, and other hyperborean races of Eurasia are shorter than their more southern neighbors, the physical record of an immemorial struggle against cold and hunger. The stunted forms and wretched aspect of the Snake Indians inhabiting the Rocky Mountain deserts distinguished these clans from the tall buffalo-hunting tribes of the plains.[42] Any feature of geographic environment tending to affect directly the physical vigor and strength of a people cannot fail to prove a potent factor in their history. [Sidenote: Physical effects of dominant activities.]