The human varieties are thus seen to be, like all other zoological species, the outcome of their several environments. They are what climate, soil, diet, pursuits and inherited characters have made them, so that all sudden transitions are usually followed by disastrous results[64]. "To urge the emigration of women and children, or of any save those of the most robust health, to the tropics, may not be to murder in the first degree, but it should be classed, to put it mildly, as incitement to it[65]." Acclimatisation may not be impossible but in all extreme cases it can be effected only at great sacrifice of life, and by slow processes, the most effective of which is perhaps Natural Selection. By this means we may indeed suppose the world to have been first peopled.
At the same time it should be remembered that we know little of the climatic conditions at the time of the first migrations, though it has been assumed that it was everywhere much milder than at present. Consequently the different zones of temperature were less marked, and the passage from one region to another more easily effected than in later times. In a word the pleistocene precursors had far less difficulty in adapting themselves to their new surroundings than modern peoples have when they emigrate, for instance, from Southern Europe to Brazil and Paraguay, or from the British Isles to Rhodesia and Nyassaland.
Correspondence of Geographical with Racial and Cultural Zones.
What is true of man must be no less true of his works; from which it follows that racial and cultural zones correspond in the main with zones of temperature, except so far as the latter may be modified by altitude, marine influences, or other local conditions. A glance at past and existing relations the world over will show that such harmonies have at all times prevailed. No doubt the overflow of the leading European peoples during the last 400 years has brought about divers dislocations, blurrings, and in places even total effacements of the old landmarks.
But, putting aside these disturbances, it will be found that in the Eastern hemisphere the inter-tropical regions, hot, moist and more favourable to vegetable than to animal vitality, are usually occupied by savage, cultureless populations. Within the same sphere are also comprised most of the extra-tropical southern lands, all tapering towards the antarctic waters, isolated, and otherwise unsuitable for areas of higher specialisation.
Similarly the sub-tropical Asiatic peninsulas, the bleak Tibetan tableland, the Pamir, and arid Mongolian steppes are found mainly in possession of somewhat stationary communities, which present every stage between sheer savagery and civilisation.
In the same way the higher races and cultures are confined to the more favoured north temperate zone, so that between the parallels of 24° and 50° (but owing to local conditions falling in the far East to 40° and under, and in the extreme West rising to 55°) are situated nearly all the great centres, past and present, of human activities—the Egyptian, Babylonian, Minoan (Aegean), Hellenic, Etruscan, Roman, and modern European. Almost the only exceptions are the early civilisations (Himyaritic) of Yemen (Arabia Felix) and Abyssinia, where the low latitude is neutralised by altitude and a copious rainfall.
Thanks also to altitude, to marine influences, and the contraction of the equatorial lands, the relations are almost completely reversed in the New World. Here all the higher developments took place, not in the temperate but in the tropical zone, within which lay the seats of the Peruvian, Chimu, Chibcha and Maya-Quiché cultures; the Aztec sphere alone ranged northwards a little beyond the Tropic of Cancer.
Thus in both hemispheres the iso-cultural bands follow the isothermal lines in all their deflections, and the human varieties everywhere faithfully reflect the conditions of their several environments.