As a young podiatrist, I used to tell patients little stories about their feet while I worked. Partly it passed the time, and partly, if I'm honest, I hoped it would convince them I knew what I was doing. One of the questions I liked best was one hardly anyone asks: why do we have toenails at all?
We rarely use our toes to pick anything up. We don't climb with them. Yet every one of them carries a nail. The answer takes us back tens of millions of years, into the trees.
Nails Are a Primate Thing
Most mammals have claws or hooves. Flat nails are almost unique to primates: monkeys, apes and us. The fossil record shows that the common ancestor of all living primates already had nails, and that it descended in turn from animals with claws.
At some point, then, our distant ancestors traded sharp, curved claws for flat plates of keratin. The question is why.
Built for Gripping
A claw is good for digging, fighting, or hooking into bark. A flat nail does something different. It sits on top of the fingertip or toe tip and gives the soft pad underneath something firm to press against. When you press down, the pad spreads out wider, which increases the area in contact with whatever you're holding. More contact means more friction, and more friction means a better grip.
That would have mattered enormously to small primates living in trees, gripping thin branches with both hands and feet. In fact, opposable big toes appear in the fossil record before opposable thumbs. Our ancestors were gripping with their feet before they were gripping with their hands.
Slow Growers
Toenails also grow far more slowly than fingernails. A study that had healthy young adults measure their own nails found that fingernails grew about 3.5 mm a month, while toenails managed only about 1.6 mm. That makes fingernails a little over twice as fast. Interestingly, the big toenail was the quickest of the toenails.
At that pace, patience is needed. If you lose a whole big toenail, through injury or treatment, it typically takes around 12 to 18 months to grow back completely. I used to warn patients about this, because a year feels like a long time to wait for a nail.
Nobody knows for certain why toenails are the slower of the two. The usual explanations are that toes get less blood flow than fingers, and that our hands take far more everyday knocks and use, which may stimulate growth. I have always privately wondered whether it also reflects the fact that we stopped using our feet to handle food and grip branches, but that is my own musing rather than established science.
So Do We Still Need Them?
Less than our ancestors did, certainly. Once humans came down from the trees and started walking upright, the foot changed from a grasping tool into a platform for standing and a lever for walking. Toes no longer needed to grip branches.
But toenails still earn their keep. They protect the ends of the toes from knocks and pressure, and they still give the toe pads that firm backing, which helps the toes press into the ground as you balance and walk.
From a podiatrist's chair, there is an irony here. A structure that evolved for life in the trees now spends its days squeezed inside shoes, and that mismatch causes a great deal of trouble. Ingrown toenails, thickened nails and nails damaged by tight or short footwear were among the most common things I treated.
The Bottom Line
Your toenails are a souvenir of our tree-climbing past, when primates gripped branches with their feet and nails helped them do it. We don't need them the way our ancestors did, but they still protect our toes and help us stand steady. Look after them, and give them room in your shoes.
Sources
- Why do humans have toenails? — Popular Science
- Curious Kids: why do we have fingernails and toenails? — The Conversation
- Average fingernail and toenail growth rate — BioNumbers (Harvard), citing Yaemsiri et al., 2010