Why are we all different colours? And why aren't we stripy or spotty like the other animals? In the latest episode of Let's Dive In Julie and Phil are here to answer another great question from a listener.

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Julie takes up the task of answering this question here...

One of my favourite films as a kid was the Wizard of Oz, particularly the bit where Dorothy gets to the mythical town of Oz for the first time, and sees this amazing horse:

"What kind of a horse is that? I've never seen a horse like that before?"

"No. and never will again I fancy. There’s only one of him and he’s it. He’s the horse of a different colour you’ve heard tell about!"

And as Dorothy and her friends ride in the back of the horse-drawn cab around the Merry Ol’ Land of Oz, we can see it change its colour from white, to purple to red to yellow!

Julie loves the Wizard of Oz!

And with Halloween coming up, and the kids getting their outfits ready (witch/ wizard, Hulk and a leopard), it did make me wonder, why aren’t we all different colours and patterns?

The thing is, humans are already different colours to each other. Some of us have lighter skin, others darker. And it turns out that 8-year-old Cillian has been wondering about this too.

His question for this episode was: "Why are there so many different skin colours?"

To help us answer this question we’ve got biological anthropologist Nina Jablonski. A biological anthropologist is someone who studies humans, human origins and how, over time, humans have adapted and evolved to thrive in their physical environments.

Nina has been studying why we all have different skin colours, or are differently pigmented, as Nina puts it, for decades.

"What we see in human skin is that it varies in the amount of protective pigment that it has in it," says Nina. "There are a few different substances in our skin that impart colour to it. And the most important of these is… melanin."

Melanin is a dark brown, almost black molecule and it "has the remarkable ability of absorbing visible light and UV radiation. And what melanin does is it protects us from high levels of damaging ultraviolet radiation in strong sunlight."

So the melanin is like your very own, in-built suncream. And the more you have of this "dark-brown, almost black molecule", the darker your skin will be.

Map of Predicted Human Skin Pigmentation
Map in Hammer-Aitoff projection. © George Chaplin

By comparing and contrasting various different data, biological anthropologists like Nina and her colleagues discovered that those people who live at the equator have the darkest pigmented skin, and those who live closer to the poles have lighter pigmented skin, and then there’s a gradient in between.

This matches closely the levels of ultraviolet radiation coming from the sun: there are higher levels of ultraviolet radiation at the equator than there are at the poles.

So, what has happened is that over time, over millions of years, the people who moved to the poles and settled there, didn’t need all that melanin in their skin. There wasn’t as much ultraviolet radiation to protect themselves against. So, their skin pigments became lighter as they produced less and less melanin.

We also ask Nina, how will human skin colours change in the future, and why aren’t we stripy or spotty like the leopards and zebras of the world? Tune into the show to find out!

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AND read all the Let's Dive In articles with experiments to try at home HERE!