How do fingernails and toenails grow?

Your nails have a job to do. The hard surface of your nails helps to protect the tips of your fingers and toes. We have also evolved to have nails because they help us pick things up (like food), pick things off (like bugs), and hold tightly onto things.

Nails themselves are made of keratin. This is the same substance your body uses to create hair and the top layer of your skin. You had fingernails and toenails before you were even born.

It may look like your fingernails and toenails start growing where your U-shaped cuticle begins. The cuticle is the thin layer of dead skin where your nail meets your skin. But there’s more going on under the surface. Nails start in the nail root, hidden under the cuticle.

When cells at the root of the nail grow, the new nail cells push out the old nail cells. These old cells flatten and harden, thanks to keratin, a protein made by these cells. The newly formed nail then slides along the nail bed, the flat surface under your nails. The nail bed sits on top of tiny blood vessels that feed it and give your nails their pink color. The lunula is that pale half circle just above the cuticle.

Your fingernails grow slowly — in fact, they grow about one tenth of an inch each month. At that rate it can take about 3 to 6 months to completely replace a nail.

So why did we evolve to have nails instead of claws? The answer is that nails let us do a lot of important things that you can’t do with claws.

Compare your nails to those of a dog or cat. Your nails are wide, flat and shield-shaped. They are also on the back of the tip of your fingers and toes.

A dog or cat has claws that are thin, curved and pointed. They wrap around the end of their “fingers” and “toes”.

Claws are great for scratching but would get in the way if you had to hold a tool or pick up something tiny. By having nails, you can pick up tiny things like small pennies or candies. You can make and use tools. Can a cat do that with its claws? No! In fact, having super-long, clawlike nails can make it really hard to do a lot of things humans need to do – like eating, washing and holding things.

Measure Fingernail Growth
Materials: permanent marker, ruler, paper, pencil

  1. Make a small mark near the center of your thumbnail with a permanent marker.
  2. Measure the distance from this mark to the base of your nail. This will be your reference point for each measurement.
  3. Measure the distance from the mark to the base of your nail every day. Record the data.
  1. Refresh the mark as needed during the course of the activity.
  2. Calculate the growth of your fingernail over a two week period.

Picking up a coin, buttoning a shirt or scratching an itch would be virtually impossible without fingernails.

We have fingernails because we are primates in the class Mammalia. Many other mammals have claws. Claws come in different shapes and sizes depending on what the animal uses them for, whether it is for scratching, clutching, digging, climbing, defense, killing and holding prey or to increase traction when running.

Amazing Claw Facts

  • The largest clawed carnivore isn’t a big cat, or even a land mammal: it’s a species of elephant seal!
  • All cats have retractable claws, except for the cheetah, whose claws are semi-retractable.
  • Wolverines are built for cold weather and their claws are built like ice-climbing boots. Wolverines use them for everything from climbing to digging. Because of this, they’re not the sharpest claws, but are incredibly strong.
  • Dewclaws in some mammals are vestigial, meaning they are remnants of toes that are less functional than other claws in modern animals.These claws aren’t in line with the others, and no longer touch the ground.
  • Beavers use oil that comes from oil glands to keep warm and dry. The second toe of each hind foot has a split nail, which the beaver uses to distribute waterproofing oil and to comb debris out of its fur.
  • A cat’s claw has layers similar to an onion. As the claw grows out, the outer layer sheds periodically, making way for a stronger, sharper version underneath.
  • A 3-foot long giant armadillo has a claw that measures nearly 8 inches.

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