[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:07.01,0:00:08.76,Default,,0000,0000,0000,,Consider the claw.
Dialogue: 0,0:00:08.76,0:00:12.49,Default,,0000,0000,0000,,Frequently found on four-limbed \Nanimals around the world,
Dialogue: 0,0:00:12.49,0:00:15.57,Default,,0000,0000,0000,,it’s one of nature’s most \Nversatile tools.
Dialogue: 0,0:00:15.57,0:00:18.89,Default,,0000,0000,0000,,Bears use claws for digging \Nas well as defense.
Dialogue: 0,0:00:18.89,0:00:23.65,Default,,0000,0000,0000,,An eagle’s needle-like talons can pierce \Nthe skulls of their prey.
Dialogue: 0,0:00:23.65,0:00:27.57,Default,,0000,0000,0000,,And lions can retract their massive claws \Nfor easy movement,
Dialogue: 0,0:00:27.57,0:00:29.94,Default,,0000,0000,0000,,before flicking them out to hunt.
Dialogue: 0,0:00:29.94,0:00:35.40,Default,,0000,0000,0000,,Even the ancestors of primates used to \Nwield these impressive appendages,
Dialogue: 0,0:00:35.40,0:00:39.78,Default,,0000,0000,0000,,until their claws evolved into nails.
Dialogue: 0,0:00:39.78,0:00:44.87,Default,,0000,0000,0000,,So what in our evolutionary past led to \Nthis manicured adaptation,
Dialogue: 0,0:00:44.87,0:00:49.74,Default,,0000,0000,0000,,and what can nails do that their \Nsharper cousins can’t?
Dialogue: 0,0:00:49.74,0:00:55.57,Default,,0000,0000,0000,,When nails first appeared in the fossil \Nrecord around 55.8 million years ago,
Dialogue: 0,0:00:55.57,0:01:00.35,Default,,0000,0000,0000,,claws had already been present for \Nover 260 million years
Dialogue: 0,0:01:00.35,0:01:03.55,Default,,0000,0000,0000,,in the ancestors of mammals and reptiles.
Dialogue: 0,0:01:03.55,0:01:06.54,Default,,0000,0000,0000,,But despite the gulf of time between \Ntheir emergence,
Dialogue: 0,0:01:06.54,0:01:10.99,Default,,0000,0000,0000,,these adaptations are both part of the \Nsame evolutionary story.
Dialogue: 0,0:01:10.99,0:01:14.25,Default,,0000,0000,0000,,Both nails and claws are made of keratin—
Dialogue: 0,0:01:14.25,0:01:20.93,Default,,0000,0000,0000,,a tough, fibrous protein also found in \Nhorns, scales, hooves and hair.
Dialogue: 0,0:01:20.93,0:01:25.96,Default,,0000,0000,0000,,This protein is produced by a wedge of \Ntissue called the keratin matrix.
Dialogue: 0,0:01:25.96,0:01:28.28,Default,,0000,0000,0000,,Rich in blood vessels and nutrients,
Dialogue: 0,0:01:28.28,0:01:32.66,Default,,0000,0000,0000,,this protein factory produces an \Nendless stream of keratin,
Dialogue: 0,0:01:32.66,0:01:36.71,Default,,0000,0000,0000,,which is tightly packed into cells \Ncalled keratinocytes.
Dialogue: 0,0:01:36.71,0:01:42.24,Default,,0000,0000,0000,,These high-density cells give nails and \Nclaws their trademark toughness.
Dialogue: 0,0:01:42.24,0:01:44.63,Default,,0000,0000,0000,,Since nails evolved from claws,
Dialogue: 0,0:01:44.63,0:01:48.59,Default,,0000,0000,0000,,both adaptations produce keratinocytes \Nin the same way.
Dialogue: 0,0:01:48.59,0:01:50.79,Default,,0000,0000,0000,,The cells grow out from the matrix,
Dialogue: 0,0:01:50.79,0:01:56.30,Default,,0000,0000,0000,,emerging from the skin where they die \Nand harden into a water-resistant sheath.
Dialogue: 0,0:01:56.30,0:01:59.64,Default,,0000,0000,0000,,The primary difference between the \Ntwo keratin coverings
Dialogue: 0,0:01:59.64,0:02:01.28,Default,,0000,0000,0000,,is really just their shape,
Dialogue: 0,0:02:01.28,0:02:06.23,Default,,0000,0000,0000,,which depends on the shape of the bone \Nat the end of the animal’s digits.
Dialogue: 0,0:02:06.23,0:02:11.42,Default,,0000,0000,0000,,In claws, the bed of keratinocytes \Nconforms to a narrow finger bone,
Dialogue: 0,0:02:11.42,0:02:15.19,Default,,0000,0000,0000,,wrapping around the end of the digit \Nand radiating outwards
Dialogue: 0,0:02:15.19,0:02:17.50,Default,,0000,0000,0000,,to form a cone-shaped structure.
Dialogue: 0,0:02:17.50,0:02:21.50,Default,,0000,0000,0000,,Animals with nails, on the other hand, \Nhave much broader digits,
Dialogue: 0,0:02:21.50,0:02:26.81,Default,,0000,0000,0000,,and keratinocytes only cover the top \Nsurface of their wide bones.
Dialogue: 0,0:02:26.81,0:02:30.15,Default,,0000,0000,0000,,It’s possible that nails have simply \Npersisted as a side effect
Dialogue: 0,0:02:30.15,0:02:33.89,Default,,0000,0000,0000,,of primates evolving wider, \Nmore dexterous fingers.
Dialogue: 0,0:02:33.89,0:02:37.73,Default,,0000,0000,0000,,But given what we know about the \Nhabitats of our primate ancestors,
Dialogue: 0,0:02:37.73,0:02:43.37,Default,,0000,0000,0000,,it’s more likely that nails came with \Ntheir own powerful advantages.
Dialogue: 0,0:02:43.37,0:02:46.50,Default,,0000,0000,0000,,High in the forest canopy where \Nthese primates lived,
Dialogue: 0,0:02:46.50,0:02:50.61,Default,,0000,0000,0000,,wide finger bones and expansive \Nfinger pads were ideal
Dialogue: 0,0:02:50.61,0:02:52.74,Default,,0000,0000,0000,,for gripping narrow branches.
Dialogue: 0,0:02:52.74,0:02:56.37,Default,,0000,0000,0000,,And nails improved that grip even further.
Dialogue: 0,0:02:56.37,0:02:59.75,Default,,0000,0000,0000,,By providing a rigid surface \Nto press against,
Dialogue: 0,0:02:59.75,0:03:05.36,Default,,0000,0000,0000,,primates could splay out their pads to \Ncreate even more contact with the trees.
Dialogue: 0,0:03:05.36,0:03:09.13,Default,,0000,0000,0000,,Additionally, nails improved the \Nsensitivity of their digits
Dialogue: 0,0:03:09.13,0:03:14.23,Default,,0000,0000,0000,,by providing an extra surface to detect \Nchanges in pressure while climbing.
Dialogue: 0,0:03:14.23,0:03:17.75,Default,,0000,0000,0000,,This combination of sensitivity \Nand dexterity
Dialogue: 0,0:03:17.75,0:03:22.66,Default,,0000,0000,0000,,gave our ancestors the precise motor \Ncontrol needed to snatch up insects,
Dialogue: 0,0:03:22.66,0:03:27.83,Default,,0000,0000,0000,,pinch berries and seeds, and keep a \Nfirm grip on slim branches.
Dialogue: 0,0:03:27.83,0:03:33.79,Default,,0000,0000,0000,,The evolution of nails and the evolution \Nof opposable thumbs and toes
Dialogue: 0,0:03:33.79,0:03:35.75,Default,,0000,0000,0000,,are closely linked.
Dialogue: 0,0:03:35.75,0:03:38.60,Default,,0000,0000,0000,,And when our ancestors moved \Ndown from the trees,
Dialogue: 0,0:03:38.60,0:03:44.58,Default,,0000,0000,0000,,this flexible grasp enabled them to create\Nand wield complex tools.
Dialogue: 0,0:03:44.58,0:03:48.14,Default,,0000,0000,0000,,Even if it was possible for wide \Nfingers to sport claws,
Dialogue: 0,0:03:48.14,0:03:50.83,Default,,0000,0000,0000,,their sharp points would’ve \Nlikely interfered
Dialogue: 0,0:03:50.83,0:03:53.37,Default,,0000,0000,0000,,with these primates’ regular tasks.
Dialogue: 0,0:03:53.37,0:03:56.98,Default,,0000,0000,0000,,Claws are ideal for piercing, \Npuncturing, and hooking,
Dialogue: 0,0:03:56.98,0:04:01.94,Default,,0000,0000,0000,,but their points make grabbing difficult, \Nand potentially dangerous.
Dialogue: 0,0:04:01.94,0:04:07.55,Default,,0000,0000,0000,,However, both claws and nails are \Nused in some unexpected ways.
Dialogue: 0,0:04:07.55,0:04:10.27,Default,,0000,0000,0000,,Manatees use nails to grasp their food,
Dialogue: 0,0:04:10.27,0:04:14.21,Default,,0000,0000,0000,,and researchers think elephant toenails \Nmay sense vibrations
Dialogue: 0,0:04:14.21,0:04:16.81,Default,,0000,0000,0000,,in the ground to help them hear.
Dialogue: 0,0:04:16.81,0:04:20.68,Default,,0000,0000,0000,,Meanwhile, some primates, \Nlike the aye-ayes of Madagascar,
Dialogue: 0,0:04:20.68,0:04:22.69,Default,,0000,0000,0000,,have re-acquired claws.
Dialogue: 0,0:04:22.69,0:04:27.03,Default,,0000,0000,0000,,They use these extra-long appendages \Nto tap branches and trunks,
Dialogue: 0,0:04:27.03,0:04:31.36,Default,,0000,0000,0000,,while listening for hollow sections \Nwith their bat-like ears.
Dialogue: 0,0:04:31.36,0:04:34.05,Default,,0000,0000,0000,,When they hear an opening, \Nthey burrow into the tree
Dialogue: 0,0:04:34.05,0:04:38.83,Default,,0000,0000,0000,,and skewer grubs with their needle-like \Nmiddle finger.
Dialogue: 0,0:04:38.83,0:04:43.79,Default,,0000,0000,0000,,We’ve only scratched the surface of all \Nthe incredible ways nails and claws
Dialogue: 0,0:04:43.79,0:04:46.46,Default,,0000,0000,0000,,are used throughout the animal kingdom.
Dialogue: 0,0:04:46.46,0:04:49.61,Default,,0000,0000,0000,,But as for which of these \Nadaptations is better?
Dialogue: 0,0:04:49.61,0:04:52.58,Default,,0000,0000,0000,,That’s an answer we may never nail down.