Why are Africans black, scientifically?

 

Scientifically, nobody in the world is black.

You probably meant to ask “what’s the scientific explanation that African people tend to have very high melanin content in their skins, making their skin darker than, for instance, northern European people? ”

And then, you would be asking the question the wrong way around, because that high melanin content was the standard when humans evolved (which they did in Africa).

The real question is why there are people with paler skin, having less melanin content in their skin.

And that question is relatively simple to answer: the melanin blocks a lot of UV light from the sun, which is really cool if you live near the equator, where there is a lot of sun, and too much UV would mean a very high risk of skin cancer.

However, when people moved out of Africa, and ended up in Asia and Europe during the latter stages of the last Ice Age, it turned out there was a lot less sunlight. And that was a problem, because while too much UV can kill us, too little of it kills us too.

We need certain vitamins, and one of them is vitamin D. Without it , we die. A vitamin D deficiency can cause rickets, as well as osteoporosis - two things that would be disastrous for stone-age humans. And in order to get vitamin D into our body, we need UV light. In our skin, UV light transforms 7-dehydrocholesterol into previtamin D3, which then becomes vitamin D3. No sunlight, no vitamin D.

So in those new, colder, less sunny climates, people with less melanin in their skin, blocking less of the now precious UV light, were less prone to vitamin D deficiency, and had a better survival rate. So over time, people’s skin got lighter, having less melanin in it.

Of course, there are setbacks to it. Lighter-skinned people are more susceptible to the negative effects of UV light, meaning they get sunburned more easily, and they have a higher risk of getting skin cancer when they go out in the sun unprotected.

Conversely, darker-skinned people may suffer vitamin D deficiency when they live in a less sunny climate.

Luckily, we have invented sun-block and vitamin supplements, so these things are no longer a problem to modern humans.