So much for the one-drop rule...
"Our original estimates were that [skin color changes] occurred perhaps at a more stately pace," Jablonski says. But now they're finding that a population can be one color (light or dark) and 100 generations later -- with no intermarriage -- be a very different color. Figuring 25 years per generation (which is generous, since early humans walked naked through the world -- clothes slow down the rate), that's an astonishingly short interval.
The linked article goes on to offer an explanation for why you sometimes have dark-skinned populations living high altitude by considering the agriculture available in various parts of the world at that time (around 10000 years ago). Sounds a bit like Guns, Germs and Steel.
With literacy and the advancement of technology, eventually the collective human memory will be much longer, and humans in the year 5000 might be able to connect with their differently-coloured relatives of 2009. And then they will really question how differences in race, something as petty as skin colour, could have had such devastating consequences. But I don't think it should take 100 generations for this to happen. Surely we have got to be better than that.
