Why do some people have brown skin?

On 3 November 2005 the topic of IUB’s second to last children’s university lecture for the year was tackled by biologist Prof. Dr. Dr. Sc. Benno Meyer-Rochow and biochemist Prof. Dr. Albert Jeltsch. They took their young listeners, ages 7-13, on a journey around the world to explain the biological background of skin color.

[ Nov 03, 2005]  On the first part of the trip the children profited from Professor Meyer-Rochow’s vast travel experience – to Papua New Guinea, where all kinds of skin and hair color combinations can be found in people, to Japan, where people call green things blue, and to various other exotic places with interesting creatures. On the way they learned that colors have to do with different kinds of light, which is the reason that we see different colors in the first place. They also have to do with pigments, one of the main reasons living beings differ in color. But what is the purpose of the different color-costumes? A praying mantis for instance, hides itself in the green leaves by exactly imitating their color, and the children knew the concept behind that: “The mantis does not want to be seen so that it does not get eaten, and it also wants to sneak up to its prey unseen”, which, of course, is the concept of camouflage. A skunk, meanwhile, is very obvious, being striped black and white. It gives a warning signal: “Do not trouble me or I will spray you with nasty odor!” Another reason for being colorful is to be pretty as in the case of male ducks or people with make-up. But what about humans and their naturally different skin colors? A trip back to Papua New Guinea gave a first idea to the children, where, amongst the normally brow-skinned population, some albinos live: “These people do not have any hair or skin color due to the lack of pigments. They can not play in the sun like the others, because the brown skin is needed for protection,“ explained Prof. Meyer-Rochow showing a photo of two albino children.

This was the cue for Professor Jeltsch to take over. He first had to tackle the difficult concept of the invisible UV light as part of natural sunlight, which is very dangerous and burns unprotected skin. The children learned that the brown skin color acts like a kind of natural sunscreen, which explains why it is very useful for people to have a very dark skin who live in place with lots of sun, like Africa. But after that Albert Jeltsch put a very interesting question to his audience: “So why do not all people have dark skin? Wouldn’t that be more handy? No-one would need any suntan lotion.” The kids only knew the obvious part of the answer: “In the northern part of the world, like here in Bremen, there is not so much sun and therefore it is not so dangerous.” So they also learned, what the uses of light-colored skin are: If enough UV light reaches the deeper part of the skin, it produces Vitamin D, which is needed for healthy and strong bones. If the skin does not produce enough of that, people have to eat a lot of food containing this vitamin – mainly fish – or otherwise they get very ill. And as dark skin keeps the UV light out, very little or no Vitamin D is produced. So the children realized that both kinds of skins have their advantages, and depending on which is the more pressing problem, protection against a lot of sun or production of vital vitamins, people tend to have brown skin in hot, tropical countries while being light-skinned in the northern regions of the world.