Gunjan Dixit, India asked:
How does black skin give better survival in hot places? Black colour absorbs heat while white colour reflects it, then black colour at hot places should burn the skin, but actually it is not so. Why?
Kat - Well, basically, this all boils down to a pigment called melanin. This is the dark pigment - if you're fair skinned, you can see it in your moles; if you're dark skinned, you have a lot of melanin all over your skin. And melanin is almost like the body's natural sunscreen, it helps to protect you against the damage that ultra-violet light can do. This means that people from countries that have dark skin, they're actually much less likely to get skin cancer. Us people with very fair, pale skin, when we're exposed to a lot of sun, a lot of ultra-violet radiation, our chances of getting skin cancer are actually much higher because the UV light from the sun can really penetrate into the skin. Whereas if you have dark skin, the melanin helps to protect you. There's also an interesting argument, some recent evidence, from Nina Jablonski; we heard her talking on the show recently about this, that very deep ultra-violet radiation can actually break down folic acid, folate, in your body. Obviously, you need to protect yourself against this happening because folate is really important for healthy metabolism and also for making healthy babies. So it's probably a natural defence mechanism that's evolved in people from countries where it's very hot to tend to have dark skin and lots of melanin to protect you.