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Ask Dr. Universe: Why do we have toenails and fingernails?

Washington State University

Washington State University

Dr. Universe: Why do we have toenails and fingernails? – Chloe, 12, Texas

Dear Chloe,

Maybe you like to paint your toenails beautiful colors or admire the dirt under your fingernails when you come in from playing outside. But you’re right to notice that nails must be more than just decoration.

To learn more, I talked to my friend Edward Johnson, an assistant professor of anatomy and physiology at Washington State University.

Johnson reminded me that humans are primates, just like gorillas or orangutans. If you look closely at a primate’s hand or foot, you’ll see their nails look a lot like yours. They’re wide and flat at the ends of their fingers and toes.

Our primate relatives spend a lot of time in trees–climbing to get away from danger, searching for fruit and seeds to eat or swinging through their branches to get through the forest quickly. Some primates, like chimpanzees, climb just to have fun.

Johnson said scientists think nails make primates’ fingers and toes stronger, helping them get a better grip while they’re moving through the branches.

But nails aren’t just for primates.

Most mammals have similar hard appendages on their fingers or toes. They’re all made of keratin, a type of protein also found in claws, fur, feathers, skin, scales and more.

The keratin at the end of a type of mammal’s fingers or toes looks different depending on how the animals use their hands or feet.

Johnson told me to think of squirrels, which climb trees in a different way than primates.

“Squirrels are actually using their claws to dig into the tree when they scurry up,” he said.

Elephants have broad strips of keratin on their toes. They’re not exactly like primate toenails, but scientists think they help make elephants’ feet stronger, too.

Animals that run fast often have fewer toes with bigger pieces of keratin to protect them. Think of a horse’s foot.

“Basically, their third toe is all that’s present, and it’s covered by a huge nail, which is their hoof,” Johnson said.

Cats need sharp claws for hunting. Instead of five toes, like you, they’ve got four, plus a small toe called a dewclaw on the back of their feet.

Human fingernails have special uses, too. Other primates have trouble picking up small objects, but humans are great at it. Your thin fingernails at the ends of your flexible fingers help. Imagine trying to pick up a tiny bead or skinny needle without your fingernails!

The next time you’re playing, maybe even climbing a tree, notice all the things you do with your hands and feet – and remember all the amazing ways animals’ bodies help them move.

Sincerely,

Dr. Universe

Know a kid with a science question? Adults can help kids submit a question at askdruniverse.wsu.edu/ask.

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