rather than anticipating further genetic branching, darwin predicts a multiracial convergence within the human genome. through modern medicine and climatization technology, caucasians now thrive within tropical environments. still, caucasians light complexion remains vulnerable to the suns ultraviolet radiation. in contrast, equatorial hominids have little difficulty surviving harsh winter conditions. for this reason, darwin envisions a monolithic, dark-skinned race exclusively comprising the worlds population, even now arctic man can live comfortably in the tropics by cooling his dwellings with the help of physical science, and by resisting the tropical diseases with the help of medical science, and the converse is equally true of equatorial man in the cold regions. it seems likely then that man will not diverge from one species into two on account of climate; indeed a convergence is more probable. thus although the fair-skinned man can make a success of living in the tropics by taking the trouble to control his climate, his fair skin is still some handicap to him, since it cannot so easily protect him against the direct rays of the sun as would a dark skin. on the other hand, there is not much evidence that a dark skin is a handicap in cold climates. if this contrast of effects is correct, it suggests that in the end man's complexion will be rather dark all over the world. curiously, darwin neglects to mention how this racial convergence will manifest in a world of geographic isolation. darwin is undoubtedly referencing elitist designs for mass migration of non-white populations into the european and north american continents. his flimsy justification based on the biological merits of epidermal complexion is simply a means towards these political ends.
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