• Question: why is it that people/creatures in hot countries are heat-absorbing colours, while people/creatures in colder countries are heat-reflecting colours?

    Asked by shrike to Gioia, Iain, Jo, Leo, Mariam on 16 Jun 2010 in Categories: .
    • Photo: Mariam Orme

      Mariam Orme answered on 16 Jun 2010:

      Dark-skinned people have lots of a pigment called melanin in their skin, which is what gives it the dark colour. Melanin helps to protect you from sunlight – it ‘soaks up’ some of the UV radiation, stopping it from causing damage to skin cells. So if you’re from a hot country where you will be exposed to a lot of sunlight, you need to have dark skin to protect you. People in colder countries, for example the UK, aren’t exposed to so much sunlight :-(so over many thousands of years they have lost a lot of the melanin in their skin, because it’s not necessary.

      Good question!

    • Photo: Iain Moal

      Iain Moal answered on 16 Jun 2010:

      There are two reason that people tend to have darker skin in warmer countries. One is because they spend more time in the sun and so go darker, like a sun tan. The other reason is genetic – they are born with darker skin. Dark skin protects people from the sun, and stops them from burning, and developing skin cancer.

      Now, humans evolved in Africa, and then spread around the world. The original skin colour was dark. The reason why people in colder countries evolved to have light skin is generally thought to be because of vitamin D. The way our body makes vitamin D is by a photochemical reaction in the skin and dark skin can block the light which makes the reaction happen. This doesn’t make a different if you are in a really sunny country, but it makes a difference if you don’t get much light.

      Now, if you don’t have enough vitamin D, your bones don’t develop properly. Women with the deficiency often have a deformed pelvis which means they cannot have children. If they get pregnant, they often die. Hence, of the people who emerged out of Africa to colder countries, those with ligher skin were more likely to have children and pass on their genes for lighter skin, which is why people in colder countries have ligher skin.

      Nowadays, we get enought vitamin D in our diet, which is why dark skinned women don’t suffer from vitamin D deficiency in cold places like the UK. Unfortunately, eskimos still suffer from it, because they hardly see any sun at all, and their diet doesn’t have much vitamin D.

    • Photo: Joanna Watson

      Joanna Watson answered on 16 Jun 2010:

      I agree with what Iain and Mariam said.
      Also for some animals, the colour they are is a good way of hiding from things that might eat them, or that they want to eat – so arctic foxes are white to blend in with the snow, but desert foxes are sandy coloured to blend in with the sand.

    • Photo: Leo Garcia

      Leo Garcia answered on 16 Jun 2010:

      What determines the colour of people’s skin is the amount of the chemical ‘melanin’ in the upper layer of the skin. The more melanin, the darker the skin.

      In humans, exposing the skin to sunlight helps make vitamin D – which is good for us. Now, if there is a lot of melanin in the skin, and little sunlight, then this can result in vitamin D deficiency, which would be bad for us (if we didn’t get our vitamin D from anywhere else – which we can!).

      Everyone’s ancestors came from Africa – where high levels of melanin help protect the body against UV radiation from the sun. As humans migrated out towards less sunny regions of the earth (like rainy old England), natural selection caused a trend towards lighter skin with less melanin – to increase the amount of sunlight absorbed.

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