Thus, though all will be dark-skinned, the South Americans will be coppery, the Africans black, and the men of Borneo yellow.
Led on by such discrepancies, perhaps, he will want next to set his world of man in movement.

He will thereupon perceive a circulation, so to speak, amongst the various peoples, suggestive of interrelations of a new type.

Now so long as he is dealing in descriptions of a detached kind, concerning not merely the physical environment, but likewise the social adjustments more immediately corresponding thereto, he will be working at the geographical level.

Directly it comes, however, to a generalized description or historical explanation, as when he seeks to show that here rather than there a civilization is likely to arise, geographical considerations proper will not suffice.

Distribution is merely one aspect of evolution.