Claws vs nails - Matthew Borths

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Consider the claw. Frequently found on animals around the world, it’s one of nature’s most versatile tools. Bears use claws for digging as well as defense. An eagle’s needle-like talons can pierce the skulls of their prey. Even the ancestors of primates used to wield these impressive appendages, until their claws evolved into nails. So what caused this adaptation? Matthew Borths investigates.

Lesson by Matthew Borths, directed by Augenblick Studios.

Consider the claw.

Frequently found on four-limbed
animals around the world,

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

Bears use claws for digging
as well as defense.

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

And lions can retract their massive claws
for easy movement,

before flicking them out to hunt.

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

until their claws evolved into nails.

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

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

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

claws had already been present for
over 260 million years

in the ancestors of mammals and reptiles.

But despite the gulf of time between
their emergence,

these adaptations are both part of the
same evolutionary story.

Both nails and claws are made of keratin—

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

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

Rich in blood vessels and nutrients,

this protein factory produces an
endless stream of keratin,

which is tightly packed into cells
called keratinocytes.

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

Since nails evolved from claws,

both adaptations produce keratinocytes
in the same way.

The cells grow out from the matrix,

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

The primary difference between the
two keratin coverings

is really just their shape,

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

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

wrapping around the end of the digit
and radiating outwards

to form a cone-shaped structure.

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

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

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

of primates evolving wider,
more dexterous fingers.

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

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

High in the forest canopy where
these primates lived,

wide finger bones and expansive
finger pads were ideal

for gripping narrow branches.

And nails improved that grip even further.

By providing a rigid surface
to press against,

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

Additionally, nails improved the
sensitivity of their digits

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

This combination of sensitivity
and dexterity

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

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

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

are closely linked.

And when our ancestors moved
down from the trees,

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

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

their sharp points would’ve
likely interfered

with these primates’ regular tasks.

Claws are ideal for piercing,
puncturing, and hooking,

but their points make grabbing difficult,
and potentially dangerous.

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

Manatees use nails to grasp their food,

and researchers think elephant toenails
may sense vibrations

in the ground to help them hear.

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

have re-acquired claws.

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

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

When they hear an opening,
they burrow into the tree

and skewer grubs with their needle-like
middle finger.

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

are used throughout the animal kingdom.

But as for which of these
adaptations is better?

That’s an answer we may never nail down.