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Consider the claw.

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Frequently found on four-limbed 
animals around the world,

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it’s one of nature’s most 
versatile tools.

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Bears use claws for digging 
as well as defense.

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

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And lions can retract their massive claws 
for easy movement,

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before flicking them out to hunt.

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Even the ancestors of primates used to 
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 
this manicured adaptation,

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

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

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claws had already been present for 
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 
their emergence,

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these adaptations are both part of the 
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 
horns, scales, hooves and hair.

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

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Rich in blood vessels and nutrients,

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this protein factory produces an 
endless stream of keratin,

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which is tightly packed into cells 
called keratinocytes.

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

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Since nails evolved from claws,

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both adaptations produce keratinocytes 
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 
and harden into a water-resistant sheath.

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The primary difference between the 
two keratin coverings

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is really just their shape,

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

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

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wrapping around the end of the digit 
and radiating outwards

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to form a cone-shaped structure.

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

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

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

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of primates evolving wider, 
more dexterous fingers.

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

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

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High in the forest canopy where 
these primates lived,

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wide finger bones and expansive 
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 
to press against,

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

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Additionally, nails improved the 
sensitivity of their digits

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

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This combination of sensitivity 
and dexterity

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

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

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The evolution of nails and the evolution 
of opposable thumbs and toes

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are closely linked.

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And when our ancestors moved 
down from the trees,

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

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

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their sharp points would’ve 
likely interfered

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with these primates’ regular tasks.

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Claws are ideal for piercing, 
puncturing, and hooking,

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but their points make grabbing difficult, 
and potentially dangerous.

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However, both claws and nails are 
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 
may sense vibrations

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in the ground to help them hear.

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Meanwhile, some primates, 
like the aye-ayes of Madagascar,

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have re-acquired claws.

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

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

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When they hear an opening, 
they burrow into the tree

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and skewer grubs with their needle-like 
middle finger.

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We’ve only scratched the surface of all 
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 
adaptations is better?

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That’s an answer we may never nail down.