WEBVTT

00:00:07.006 --> 00:00:08.756
Consider the claw.

00:00:08.756 --> 00:00:12.486
Frequently found on four-limbed 
animals around the world,

00:00:12.486 --> 00:00:15.566
it’s one of nature’s most 
versatile tools.

00:00:15.566 --> 00:00:18.888
Bears use claws for digging 
as well as defense.

00:00:18.888 --> 00:00:23.648
An eagle’s needle-like talons can pierce 
the skulls of their prey.

00:00:23.648 --> 00:00:27.567
And lions can retract their massive claws 
for easy movement,

00:00:27.567 --> 00:00:29.940
before flicking them out to hunt.

00:00:29.940 --> 00:00:35.405
Even the ancestors of primates used to 
wield these impressive appendages,

00:00:35.405 --> 00:00:39.785
until their claws evolved into nails.

00:00:39.785 --> 00:00:44.867
So what in our evolutionary past led to 
this manicured adaptation,

00:00:44.867 --> 00:00:49.740
and what can nails do that their 
sharper cousins can’t?

NOTE Paragraph

00:00:49.740 --> 00:00:55.570
When nails first appeared in the fossil 
record around 55.8 million years ago,

00:00:55.570 --> 00:01:00.349
claws had already been present for 
over 260 million years

00:01:00.349 --> 00:01:03.548
in the ancestors of mammals and reptiles.

00:01:03.548 --> 00:01:06.540
But despite the gulf of time between 
their emergence,

00:01:06.540 --> 00:01:10.991
these adaptations are both part of the 
same evolutionary story.

00:01:10.991 --> 00:01:14.253
Both nails and claws are made of keratin—

00:01:14.253 --> 00:01:20.926
a tough, fibrous protein also found in 
horns, scales, hooves and hair.

00:01:20.926 --> 00:01:25.956
This protein is produced by a wedge of 
tissue called the keratin matrix.

00:01:25.956 --> 00:01:28.275
Rich in blood vessels and nutrients,

00:01:28.275 --> 00:01:32.665
this protein factory produces an 
endless stream of keratin,

00:01:32.665 --> 00:01:36.711
which is tightly packed into cells 
called keratinocytes.

00:01:36.711 --> 00:01:42.241
These high-density cells give nails and 
claws their trademark toughness.

NOTE Paragraph

00:01:42.241 --> 00:01:44.627
Since nails evolved from claws,

00:01:44.627 --> 00:01:48.588
both adaptations produce keratinocytes 
in the same way.

00:01:48.588 --> 00:01:50.788
The cells grow out from the matrix,

00:01:50.788 --> 00:01:56.297
emerging from the skin where they die 
and harden into a water-resistant sheath.

00:01:56.297 --> 00:01:59.637
The primary difference between the 
two keratin coverings

00:01:59.637 --> 00:02:01.278
is really just their shape,

00:02:01.278 --> 00:02:06.228
which depends on the shape of the bone 
at the end of the animal’s digits.

00:02:06.228 --> 00:02:11.417
In claws, the bed of keratinocytes 
conforms to a narrow finger bone,

00:02:11.417 --> 00:02:15.193
wrapping around the end of the digit 
and radiating outwards

00:02:15.193 --> 00:02:17.497
to form a cone-shaped structure.

00:02:17.497 --> 00:02:21.501
Animals with nails, on the other hand, 
have much broader digits,

00:02:21.501 --> 00:02:26.811
and keratinocytes only cover the top 
surface of their wide bones.

NOTE Paragraph

00:02:26.811 --> 00:02:30.149
It’s possible that nails have simply 
persisted as a side effect

00:02:30.149 --> 00:02:33.886
of primates evolving wider, 
more dexterous fingers.

00:02:33.886 --> 00:02:37.733
But given what we know about the 
habitats of our primate ancestors,

00:02:37.733 --> 00:02:43.373
it’s more likely that nails came with 
their own powerful advantages.

NOTE Paragraph

00:02:43.373 --> 00:02:46.503
High in the forest canopy where 
these primates lived,

00:02:46.503 --> 00:02:50.607
wide finger bones and expansive 
finger pads were ideal

00:02:50.607 --> 00:02:52.744
for gripping narrow branches.

00:02:52.744 --> 00:02:56.367
And nails improved that grip even further.

00:02:56.367 --> 00:02:59.749
By providing a rigid surface 
to press against,

00:02:59.749 --> 00:03:05.361
primates could splay out their pads to 
create even more contact with the trees.

00:03:05.361 --> 00:03:09.126
Additionally, nails improved the 
sensitivity of their digits

00:03:09.126 --> 00:03:14.226
by providing an extra surface to detect 
changes in pressure while climbing.

00:03:14.226 --> 00:03:17.748
This combination of sensitivity 
and dexterity

00:03:17.748 --> 00:03:22.658
gave our ancestors the precise motor 
control needed to snatch up insects,

00:03:22.658 --> 00:03:27.827
pinch berries and seeds, and keep a 
firm grip on slim branches.

00:03:27.827 --> 00:03:33.794
The evolution of nails and the evolution 
of opposable thumbs and toes

00:03:33.794 --> 00:03:35.749
are closely linked.

00:03:35.749 --> 00:03:38.602
And when our ancestors moved 
down from the trees,

00:03:38.602 --> 00:03:44.580
this flexible grasp enabled them to create
and wield complex tools.

NOTE Paragraph

00:03:44.580 --> 00:03:48.138
Even if it was possible for wide 
fingers to sport claws,

00:03:48.138 --> 00:03:50.830
their sharp points would’ve 
likely interfered

00:03:50.830 --> 00:03:53.369
with these primates’ regular tasks.

00:03:53.369 --> 00:03:56.978
Claws are ideal for piercing, 
puncturing, and hooking,

00:03:56.978 --> 00:04:01.938
but their points make grabbing difficult, 
and potentially dangerous.

00:04:01.938 --> 00:04:07.552
However, both claws and nails are 
used in some unexpected ways.

00:04:07.552 --> 00:04:10.267
Manatees use nails to grasp their food,

00:04:10.267 --> 00:04:14.212
and researchers think elephant toenails 
may sense vibrations

00:04:14.212 --> 00:04:16.812
in the ground to help them hear.

00:04:16.812 --> 00:04:20.678
Meanwhile, some primates, 
like the aye-ayes of Madagascar,

00:04:20.678 --> 00:04:22.694
have re-acquired claws.

00:04:22.694 --> 00:04:27.029
They use these extra-long appendages 
to tap branches and trunks,

00:04:27.029 --> 00:04:31.355
while listening for hollow sections 
with their bat-like ears.

00:04:31.355 --> 00:04:34.050
When they hear an opening, 
they burrow into the tree

00:04:34.050 --> 00:04:38.830
and skewer grubs with their needle-like 
middle finger.

NOTE Paragraph

00:04:38.830 --> 00:04:43.788
We’ve only scratched the surface of all 
the incredible ways nails and claws

00:04:43.788 --> 00:04:46.463
are used throughout the animal kingdom.

00:04:46.463 --> 00:04:49.614
But as for which of these 
adaptations is better?

00:04:49.614 --> 00:04:52.584
That’s an answer we may never nail down.