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Consider the claw.

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Frequently found on four-limbed [br]animals around the world,

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it’s one of nature’s most [br]versatile tools.

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Bears use claws for digging [br]as well as defense.

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An eagle’s needle-like talons can pierce [br]the skulls of their prey.

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And lions can retract their massive claws [br]for easy movement,

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before flicking them out to hunt.

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Even the ancestors of primates used to [br]wield these impressive appendages,

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until their claws evolved into nails.

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So what in our evolutionary past led to [br]this manicured adaptation,

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and what can nails do that their [br]sharper cousins can’t?

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When nails first appeared in the fossil [br]record around 55.8 million years ago,

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claws had already been present for [br]over 260 million years

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in the ancestors of mammals and reptiles.

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But despite the gulf of time between [br]their emergence,

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these adaptations are both part of the [br]same evolutionary story.

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Both nails and claws are made of keratin—

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a tough, fibrous protein also found in [br]horns, scales, hooves and hair.

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This protein is produced by a wedge of [br]tissue called the keratin matrix.

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Rich in blood vessels and nutrients,

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this protein factory produces an [br]endless stream of keratin,

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which is tightly packed into cells [br]called keratinocytes.

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These high-density cells give nails and [br]claws their trademark toughness.

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Since nails evolved from claws,

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both adaptations produce keratinocytes [br]in the same way.

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The cells grow out from the matrix,

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emerging from the skin where they die [br]and harden into a water-resistant sheath.

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The primary difference between the [br]two keratin coverings

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is really just their shape,

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which depends on the shape of the bone [br]at the end of the animal’s digits.

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In claws, the bed of keratinocytes [br]conforms to a narrow finger bone,

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wrapping around the end of the digit [br]and radiating outwards

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to form a cone-shaped structure.

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Animals with nails, on the other hand, [br]have much broader digits,

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and keratinocytes only cover the top [br]surface of their wide bones.

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It’s possible that nails have simply [br]persisted as a side effect

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of primates evolving wider, [br]more dexterous fingers.

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But given what we know about the [br]habitats of our primate ancestors,

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it’s more likely that nails came with [br]their own powerful advantages.

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High in the forest canopy where [br]these primates lived,

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wide finger bones and expansive [br]finger pads were ideal

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for gripping narrow branches.

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And nails improved that grip even further.

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By providing a rigid surface [br]to press against,

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primates could splay out their pads to [br]create even more contact with the trees.

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Additionally, nails improved the [br]sensitivity of their digits

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by providing an extra surface to detect [br]changes in pressure while climbing.

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This combination of sensitivity [br]and dexterity

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gave our ancestors the precise motor [br]control needed to snatch up insects,

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pinch berries and seeds, and keep a [br]firm grip on slim branches.

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The evolution of nails and the evolution [br]of opposable thumbs and toes

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are closely linked.

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And when our ancestors moved [br]down from the trees,

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this flexible grasp enabled them to create[br]and wield complex tools.

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Even if it was possible for wide [br]fingers to sport claws,

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their sharp points would’ve [br]likely interfered

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with these primates’ regular tasks.

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Claws are ideal for piercing, [br]puncturing, and hooking,

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but their points make grabbing difficult, [br]and potentially dangerous.

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However, both claws and nails are [br]used in some unexpected ways.

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Manatees use nails to grasp their food,

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and researchers think elephant toenails [br]may sense vibrations

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in the ground to help them hear.

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Meanwhile, some primates, [br]like the aye-ayes of Madagascar,

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have re-acquired claws.

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They use these extra-long appendages [br]to tap branches and trunks,

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while listening for hollow sections [br]with their bat-like ears.

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When they hear an opening, [br]they burrow into the tree

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and skewer grubs with their needle-like [br]middle finger.

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We’ve only scratched the surface of all [br]the incredible ways nails and claws

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are used throughout the animal kingdom.

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But as for which of these [br]adaptations is better?

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That’s an answer we may never nail down.