Is there a reason for toenails?

08 September 2015

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Question

Why do we have toenails?

Answer

Fingernails seem to have obvious uses but what are our toenails for? Sam Mahaffey and Dr Isabelle Winder from the University of York go in search of a gripping answer...

Sam - Well, this question got us Naked Scientists talking. What is the point of toenails? Gary on Facebook thinks they must’ve benefitted our ancestors at some point, and Gerald says that our nails gives support when gripping. I asked Dr Isabelle Winder, a paleoanthropologist at the University of York to help me answer this one…

Isabelle - Our nails evolved from claws. Primates all have flat nails like ours although not all of them have nails on every finger and toe. The small lemurs and lorises for example have a special grooming claw on some of their toes.

Sam - I'm not sure I like the sound of the grooming claw. How did we go from claws to nails then?

Isabelle - Nails appeared when the early primates grew larger and moved into the smaller branches of the trees where the fruits, seeds, flowers, and insects are. Claws are strong enough to bear the weight of small bodied animals – think of a squirrel. But a larger animal can't put all its weight on small claws so the larger primates evolved a strong grip and fingers and toes that can grasp efficiently instead. We don’t know if this change especially favoured nails or is there a by-product of the evolution of grasping hands and feet? But they're part of the same package that gave us opposable thumbs.

Sam - Okay. Our nails evolved from claws and this was part and parcel of our dextrose hand and feet. But do nails serve any purpose now, other than looking nice when we paint them different colours?

Isabelle - Well, their main job is to protect the sensitive ends of our fingers and toes from damage. They also help us with precision movements. When you touch another object, the soft tissues in your finger push against our nail which provides a solid anchor and enhanced sensitivity. It’s even been suggested that nails may serve us as indicators of health because poor diet and disease often show up in changes to the colour, condition, and strength of our nails. Of course, we can use our nails themselves as tools.

Sam - Okay. I can see why our fingernails would be useful as tools for picking, peeling, and scratching, but what about our toenails? I can't peel an orange with my toenails. Even if I could, I don’t think I’d want to. In fact, it seems like our toenails actually cause us problems like when they become ingrown and maybe we’d be better off without them. Are our toenails at all advantageous? If not, might we one day evolve to lose them?

Isabelle - I suspect you're right that toenails aren’t as useful or essential to our modern lives as fingernails. I think some of the same functions, protection for instance are applicable. But now that our toes have lost their role in grasping, we probably need them significantly less. But personally, I don’t think we’re going to evolve to lose our toenails mostly because to see a change like that, I’d expect there to be a benefit to not having them rather than a small benefit to keeping them.

Sam - So, our toenails might not be very useful to us, but unless there will be some evolutionary benefit to losing them, it looks like they're here to stay. Perhaps Rachel on Facebook is right. Toenails are just something to decorate. I hope that answered your question (Lou Allan). Next week, I’ll be trying to fathom Paul’s question…

Paul - Why do we make mistakes during repetitive tasks?

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