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Curiosities: Why do we have fingernails?

May 21, 2007

Fingernails are essentially flattened versions of claws, and they evolved in all primates — including humans — to support broad fingertips, says UW–Madison anthropology professor John Hawks.

Monkeys, apes and lemurs spend a lot of time in trees, and broad fingertips help give them the strong grip needed to climb trunks and hang underneath branches.

Of course, other animals, like cats and squirrels, climb trees, too. But they do so with their claws, rather than by grabbing branches the primate way. “It’s basically a different strategy for climbing,” says Hawks.

As primates, we not only inherited broad fingertips, but ours are even wider than those of our closest kin, such as chimpanzees and orangutans, Hawks says. The reason for this dates back to the earliest days of human tool use: Striking stones together to make tools requires a very powerful grip.

Although the switch to fingernails has served primates well, Hawks reminds us “claws are just better for some things.” That’s why, in addition to their nails, lemurs have kept a claw for grooming their fur. One lemur, the Aye-aye, has even retained two, one of which sits at the end of a long, bony finger.

The Aye-aye uses this claw to drag insects and grubs out of holes. Try doing that with a fingernail.