Our fingernails are similar to claws or hooves found in other animals. More generally called “digital appendages”, they are enlarged keratinized structures (the same stuff that horns are made out of) that protect the tips of the fingers and toes in most vertebrate species, or animals with backbones. Fingernails are broad, and slightly curved, and mostly cover the top surface of our fingers.
In other species, this structure is slightly different – for example, crocodiles have a thimble-shaped structure that covers the whole tip of their digits, whereas hawks and owls have talons, highly recurved claws specialized for prey capture, and horses and cows have hooves that protect their feet.
So, the reason we have fingernails is simply that everyone in our family tree has some sort of digital appendage that probably served to protect fingertips in our distant ancestors, and each group has evolved modifications that best fit their needs for a particular environment. Fingernails in monkeys, apes and humans always cover only one side of the fingertip and thus they protect but don’t limit the motion or sensitivity of our fingertips.
Ph.D. University of Washington, Seattle
Vertebrate evolutionary biology
husband Harry (also a scientist), and one canine friend, Riley
hiking, long-distance running
West Middle School