When living naked in the open, skin colour is vital to survival.
Skin too dark for the area, not enough vitamin D is made, people get ill or die of influenza and rickets.
Skin too light for the area, not enough protection from the sun's rays, skin cancer.
When you have a small population with a natural variation in skin colour, these pressures will leave the ones with the most appropriate colour for the
area able to stay healthy and pass on their genes, and those less blessed will be less healthy and less able to produce offspring.
What humans consider beauty has always had a strong correlation with health and fertility. Instinctively we look for someone we can make health babies
with. So it's not surprising that, under these circumstances, outward appearances rapidly changed.
As we now spend most of out time indoors and wear clothing, natural selection in terms of skin colour is not applicable in the same way, so people in
our societies are unlikely to change so quickly again.
A unified human preference for a certain type of mating partner could influence a change, as the non-selected types died out, but people of all
appearances are still managing to reproduce. Love can be blind, or desperate, or kinky, and there's always beer.
edit on 11/12/10 by Kailassa because: (no reason given)