3 Questions about skin color

[Nobody]

@Lamia

I hope I’m not mangling my genetics here, but I think it would take much longer for a light-skinned population to evolve dark skin in response to their environment than it would for a dark-skinned population to do the reverse. The genes for dark coloring, be it skin, hair, or eye, are dominant, right? So darkly pigmented people can be (and often are) carriers for lighter genes, but lightly pigmented people cannot be carriers for darker genes.

Genes don’t just come out of nowhere, so a mutation would have to occur before our light-skinned population could begin to produce darker offspring. As mutations are, by their very nature, random, this could take a really long time. If the dark-skinned population did include carriers of lighter genes, no initial mutation would be necessary before natural selection could start doing its thing in response to new environmental pressures.

Actually, I’m glad that you brought that point up, because I was wondering about it.

[Sinungaling]

The theory that dark skin = protection against sun breaks down on at least two points.

The first has already been mentioned, the fact that the Inuit aren’t very fair-skinned.

The second point is that equatorial regions are, or were, covered with rainforests. The vegetation is so dense that rainforests are amazingly dark even on really bright and sunny days. Meaning that the dark skin of equatorial people supposedly protects them against greater amounts of non-existent sunlight. In fact, the Sahara desert is probably the sunniest place on the planet, and going with the “dark skin as sun protection” theory, Arabs should be the darkest people on earth. Clearly, they’re not, strongly suggesting that there’s no 1:1 correlation between levels of sunlight in the environment and levels of melanin in humans.

[Broomstick]

Then again, the Arabs wear a lot of clothing, which would mitigate much of the effects of the sun. Also, how long have the Arabs been living where they currently are? That, too, would have an effect. Other people from the region, such as the Sudanese I mentioned, are some of the darkest people in the world

As for the “dominance” or “recessiveness” of color genes - it’s much more complicated than that. More than one pair of genes are at work. So two medium-brown parents can produce children both lighter and darker than themselves, depending on how the genes sort out by random chance.

[Lamia]

@Broomstick

As for the “dominance” or “recessiveness” of color genes - it’s much more complicated than that. More than one pair of genes are at work. So two medium-brown parents can produce children both lighter and darker than themselves, depending on how the genes sort out by random chance.

Yes, but I understood part 3 of the OP to be referring to light-skinned white Europeans, not medium-brown white Europeans. Two stereotypically pale Nordic types can’t be carriers for darker genes, can they? And if not, they aren’t going to produce darker children unless there’s a lucky mutation first.

[Tastes_of_Chocolate]

@Sinungaling

The second point is that equatorial regions are, or were, covered with rainforests.

Some equatorial regions are covered in rainforests. Not all.

@Sinungaling

In fact, the Sahara desert is probably the sunniest place on the planet, and going with the “dark skin as sun protection” theory, Arabs should be the darkest people on earth. Clearly, they’re not, strongly suggesting that there’s no 1:1 correlation between levels of sunlight in the environment and levels of melanin in humans.

This is assuming that the peoples you now call Arabs evolved in that area. Homo sapiens have traveled widely over time, and where they are today may have little connection to where they originated.

[Acsenray]

@Master Control

1. OK, so a group of people moves from Africa and settles down somewhere else further from the equator. Now not as much melanin is needed, so children who are born with less, do better, and eventually, though, I guess, natural selection, the generations gradually get lighter until they reach a level of melanin that is best suited for their environment, right? If this is incorrect, then how did skin color variation come about?

It’s a lot more complicated than this.

One factor is that light skin colour = higher susceptibility to skin cancer

Another factor is that light skin colour = more production of Vitamin D = better able to extract calcium from cow’s milk – of course, this has to go hand-in-hand with lactase sufficiency

So it’s not just a matter of “level of melalnin that is best suited for their environment” – it’s a tradeoff – who’s going to be more likely to produce offspring in an environment in which cow’s milk is the only source of calcium – someone who is more susceptible to skin cancer or someone who is more susceptible to brittle bones/constant diarrhoea/chronic flatulence?