Cosmo: Hey, Doctor Universe.
Dr. Universe: Hey, Cosmo.
Cosmo: Did you know giraffes can grow up to eighteen feet?
Dr. Universe: Oh, wow.
Cosmo: But most only have four.
Dr. Universe: Hey, friends, I'm Doctor Universe.
Cosmo: And I'm Cosmo.
Dr. Universe: And if you're anything like us, you've got lots of big questions about our world. Today, we're answering a question sent in by a kid just like you.
Cosmo: Winona wants to know: why are giraffes' tongues purple?
Dr. Universe: When I was a kitten, I visited a drive-through zoo. A giraffe slithered its long purple tongue through the open window and licked my face.
Cosmo: Gross.
Dr. Universe: It was awesome.
It turns out dark colors come from a pigment called melanin. That melanin makes a giraffe's tongue purple, blue, or black. Melanin is also why human skin gets darker from being in the sun
Cosmo: Like how some humans get a suntan.
Dr. Universe: Skin is layers of mostly skin cells. And those skin cells have a nucleus full of DNA. DNA tells our cells how to make proteins. You need all kinds of proteins to build your body and make it work. So every cell needs a perfect copy of DNA without any mistakes.
But UV light from the sun can mess up DNA.
Cosmo: And that's not good.
Dr. Universe: That's where melanin comes in. It protects the DNA in skin cells from that damage. Melanin-making cells are scattered through the layers of skin cells. There's usually one melanin-making cell for every forty skin cells. The melanin-making cells have finger-like extensions that reach out to contact all the skin cells nearby.
When the sun shines on skin, the light activates those melanin-making cells. They start churning out sacs of melanin. Then they reach out to the skin cells they touch and move sacs of melanin over there.
Cosmo: That's very generous.
Dr. Universe: The goal is to safeguard the DNA. You can picture it like a flying saucer hovering over the nucleus. Or an umbrella the melanin-making cells open up to block the DNA from the sun. When those sacs of melanin move into a skin cell, the melanin pigment makes the cell darker. That's how skin gets browner in the sun.
Cosmo: So a suntan is evidence your skin is protecting you from the sun.
Dr. Universe: It works so well to protect DNA that humans living in places with lots of sun adapted to protect their skin better. Genetic changes led people to have different skin tones, like darker skin near the equator, where there's lots of sun, and lighter skin near the poles, where there's less sun.
Dr. Universe: And that's probably why giraffes have purple tongues. The ancestors of giraffes adapted to live in places with lots of sun. Plus, today's giraffes are the tallest living land animals.
Cosmo: They spend about twelve hours every day chomping on leaves at the top of trees.
Dr. Universe: They grab those leaves with a purple prehensile tongue. It works like a slimy, muscular tentacle. The melanin in the tongue protects the DNA in the tongue skin cells.
Cosmo: I guess you could say giraffes really lick the problem of UV damage.
Dr. Universe: That's all for this episode, friends.
Cosmo: Big thanks to Cynthia Cooper, a biologist at Washington State University.
Dr. Universe: As always, if you've got a science question for me, you can submit it at askdruniverse.wsu.edu. That's a s k d r u n i v e r s e dot w s u dot e d u. Who knows where your questions will take us next?
