There is a theory afloat, that it is only in temperate climates that barbarous nations make much progress in civilizing themselves.

In tropical countries the intensity of the heat makes man little disposed for exertion, and the luxuriance of the vegetation supplies him with the little he requires.

In such climates--say the advocates of this theory--man acknowledges the supremacy of nature over himself, and gives up the attempt to shape her to his own purposes; and thus, in these countries, the inhabitants go on from generation to generation, lazily enjoying their existence, making no effort, and indeed feeling no desire to raise themselves in the social scale.

Upon this theory, therefore, when we find a high civilization in hot countries, as in the plains of India, we have to account for it by supposing an immigration of races bringing their civilization with them from more temperate climates.

This theory of civilization favours the idea of the Central American cities having been built by a people from Mexico.