How long does it take for Humans to change their Skin color? How many generations or years after Humans came north did it take for them to “loose” their dark skin?
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They had to wait for a mutation with low melanin to occur (white skin), then the advantage of higher rates of vitamin D production meant all their offspring had an evolutionary advantage over the others and so more of their offspring survived and bred the next generation eventually it becoming the dominant strain. In all it likely took over 100 generations.
We don’t really know. Evolution depends on random mutations, and the rate of mutation depends on several external factors. We also don’t know exactly how significant skin color was in terms of survival. If we did know the rate of mutation, and the fitness rates of light vs dark skin, we could make a pretty close guess but even then there would be a pretty big margin of error.
On top of that, it isn’t as if there was a sudden shift in skin tone from one generation to the next. Lighter skin is better in areas with less sunlight, but lighter is relative. The drastic difference we see today is the result of hundreds of small adjustments. Think of the light spectrum, you can’t really pinpoint the spot where red becomes orange.
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