Whether these have been acquired by centuries of extreme lung expansion, or represent the survival of a chance variation of undoubted advantage, they are a product of the environment.

They are a serious handicap when the Aymara Indian descends to the plains, where he either dies off or leaves descendants with diminishing chests.[36] [See map page 101.] [Sidenote: Stature and environment] 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.