Why are there different skin colors?

Louise:: This month's question is from Agum in Canada who asks, "Why are there different skin colours? How did that happen?" And to answer this question, I spoke to Dr. Aylwyn Scally from the Department of Genetics at the University of Cambridge.

Aylwyn:: Skin colour is like lots of human characteristics, one of these things which is predominantly determined by your genetic content. Another way of saying it is that it's determined by your ancestry, so we know the people whose ancestry comes from Africa or regions close to the equator tend to have darker skin colour and people further away in higher latitudes will have lighter skin colour. And that is something which we've recently been able to actually identify in terms of which parts of the genome and how much of our DNA is actually involved in determining skin colour.

We can say quite a lot now about when that might have happened, when these changes might have occurred, and then speculate about the reasons why they might have occurred. But there are still questions that we don't understand; we don't have the answers to. One of which is really the basic thing is, exactly why have these genetic changes taken place, what has been the benefit for people living in northern latitudes for them to have lighter skin colour? We have ideas about that and they're related to protection of the skin from UV light. That's what people have speculated about for a long time, but we don't really have a very clear cut example or reason for why that might be the case.

Alternatively, there's also the idea that when your skin is heavily pigmented, it means it protects you against UV light, but actually, you need certain amount of UV light to synthesise vitamin D in your body. So, when the amount of UV light you're getting is lower, say, when you're living in a northern climate, then that means that it's beneficial to actually increase the amount of UV light and therefore, that could be a reason why people have evolved lighter skin. We were able to look around across the whole genome and look at different regions and see where these changes have taken place, and we can see that in Europeans, it seems to have happened quite recently - recently in terms of human evolution that is. So, within the last 20,000 years or so, that's sometime around since the last Ice Age. And you can also see lighter skin colours elsewhere around the world, in Asia, but the genes involved are not necessarily the same ones. We can identify different genetic changes that you find in east Asians who also have lighter skin than Africans, our ancestors.