In making these observations, I leave out of the question the hot unhealthy coast-lands of the tierra caliente, and the cold and comparatively sterile plains of the tierra fría, and confine myself to that part of the country which lies between the altitudes of 3,000 and 8,000 feet, between which limits the European races flourish under circumstances of climate which also suited the various Mexican races, who probably came from a colder northern country. Now, if we begin to descend from the level of the Mexican plateau—say 8,000 feet above the sea—we find that less and less labour will provide nourishment for the cultivator of the soil, until we reach the limit of the banana, where the inhabitants ought to be crowded together like Chinese on their rice-grounds, or the inhabitants of Egypt in the time of Herodotus. Exactly the opposite rule takes effect; the banana-country is a mere wilderness, and the higher the traveller rises the more abundant become both present population and the remains of ancient settlements.
I suppose the reason of this is to be found in the habits and constitution of the tribes who colonized the country, and preferred to settle in a climate resembling that of their native land, without troubling themselves about the extra labour it would cost them to obtain their food. The European invaders have acted precisely in the same way; and the distribution of the white and partly white inhabitants of the country follows the same rule as that of the Indians.
So far the matter is intelligible, on the principle that the constitution and habits of the races which have successively taken up their residence in the country have been strong enough to prevail over the rule which regulates the supply of men by the abundance of food; but this does not explain the fact of an actual diminution of the inhabitants of the lower temperate districts. They were not mere migratory tribes, staying for a few years before moving forward. They had been settled in the country long enough to be perfectly acclimatized; and yet, under circumstances apparently so favourable to their increase, they have been diminishing for centuries, and are perhaps even doing so now.