THE EVOLUTION OF SKIN – PBS and NOVA Science Documentaries (full documentary) [w/ subs]

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00:00:00 – on the battlefield of nature skin has
00:00:03 – evolved weapons for predation Armour for
00:00:07 – protection and the means to move from
00:00:11 – fish to dinosaurs to us this is the
00:00:18 – incredible untold story of the organ
00:00:21 – that makes it all possible skin
00:00:27 – [Music]
00:00:29 – you
00:00:31 – [Music]
00:00:42 – the shark is famous as the killer of the
00:00:45 – Seas its jaws and teeth are the stuff of
00:00:49 – legend
00:00:50 – [Music]
00:00:51 – but the shark can't deliver its bite
00:00:54 – without its amazing speed and water even
00:00:57 – its skin is deadly you look at the
00:01:00 – structure of the teeth and the scale
00:01:01 – they're almost identical what we call
00:01:04 – dermal denticles or skin teeth that
00:01:06 – formed the entire outer layer of the
00:01:08 – skin of the shark the shark skin is
00:01:11 – razor sharp built in a tight diamond
00:01:14 – pattern so hydrodynamic that it's the
00:01:17 – basis for the advanced competitive
00:01:19 – swimsuit design and so sharp that if a
00:01:23 – predator tries to attack a shark from
00:01:25 – behind it will be badly cut there are a
00:01:29 – few creatures that can fight the shark
00:01:31 – but there are some that can hide to
00:01:35 – avoid vicious predators like sharks
00:01:38 – the octopus changes its shape color and
00:01:41 – texture in an instant to look like rock
00:01:44 – and algae
00:01:50 – in this evolutionary arms race between
00:01:53 – predator and prey you have this
00:01:55 – magnificent skin being evolved and it's
00:01:57 – in response to the visual predators that
00:02:00 – are out there skin for predation skin
00:02:05 – for escape
00:02:07 – just two of the phenomenal abilities
00:02:10 – evolved by the massive organ that seems
00:02:13 – to be a simple barrier to the outside
00:02:15 – world we don't tend to think about skin
00:02:23 – as an organs but it is unlike a heart or
00:02:26 – a liver it's an organ that is spread
00:02:29 – over the exterior of our body and we see
00:02:33 – skin performing many important functions
00:02:35 – for animals from species recognition to
00:02:38 – mating behavior to protection from
00:02:41 – predators and from the environment skin
00:02:44 – has evolved countless different ways
00:02:46 – across the animal spectrum becoming
00:02:49 – nails fur coves
00:02:52 – and horns skin has evolved to meet the
00:02:56 – different needs of different species
00:02:59 – this is an amazing course of evolution
00:03:02 – that the rudimentary cells in skin have
00:03:06 – evolved in their own course to provide
00:03:09 – in some animals hair in some feathers
00:03:13 – and in others scale
00:03:16 – but for the first 200 million years of
00:03:20 – animal evolution the story of skin was
00:03:23 – confined to the seas scientists believe
00:03:27 – that the first skin like structure to
00:03:29 – appear belong to some of the earliest
00:03:32 – animals to exist on earth
00:03:34 – jellyfish are thought to have a emerged
00:03:36 – something of the order of 700 million
00:03:39 – years ago Peter Anderson studies
00:03:43 – jellyfish to find clues about how skin
00:03:46 – first evolved the jellyfish was one of
00:03:50 – the first creatures to be able to move
00:03:52 – freely in the water encased in a single
00:03:55 – layer of cells that work together to
00:03:58 – protect and respond to the world outside
00:04:00 – it was also one of the first creatures
00:04:03 – to use a protective layer as an attack
00:04:05 – weapon sting cells since nearby prey and
00:04:10 – lash out in an instant this thing self
00:04:14 – provides the animal with a great ability
00:04:16 – to capture food and to defend itself and
00:04:19 – that is allowed them to survive so
00:04:21 – successfully
00:04:24 – but the jellyfish does not have a true
00:04:27 – skin what we recognize as skin began
00:04:30 – with vertebrate fish fish grew a
00:04:33 – two-layer covering over 500 million
00:04:36 – years ago from the start these first
00:04:41 – creatures with backbones were a success
00:04:45 – and eventually evolved into a world of
00:04:48 – animals with backbones including human
00:04:53 – beings as far as we know this
00:04:57 – evolutionarily novel structure this two
00:05:00 – layered skin first appeared in the
00:05:02 – earliest fishes the skin of vertebrates
00:05:06 – is a unique kind of structure John long
00:05:10 – is a professor of Biological Sciences at
00:05:13 – Vassar College fishes can in made-up
00:05:15 – up two very distinctive tissue layers
00:05:18 – the epidermis and the dermis the tough
00:05:22 – epidermis on the surface like the
00:05:24 – jellyfish exterior forms a barrier to
00:05:26 – the outside world but the supple dermis
00:05:30 – that lies just beneath makes all the
00:05:32 – difference this amazingly fertile system
00:05:35 – of cells would anchor the roots of many
00:05:38 – different skin structures the first of
00:05:41 – them was fish scales scales arose during
00:05:45 – a time of vicious predation in the seas
00:05:48 – the Cambrian killers like anomalocaris
00:05:54 – and the giant de costea's sliced through
00:05:57 – defenseless prey and even if dunk was
00:06:02 – avoided smaller fish battled in their
00:06:04 – own weight class some fish needed body
00:06:07 – armor just to have a chance at survival
00:06:10 – what's interesting about fish skin is
00:06:13 – that the scales in fact are made of some
00:06:17 – of the same materials that bone
00:06:18 – instructors in our teeth are made out of
00:06:21 – and the result is that fish have a
00:06:23 – strong sturdy layer essentially a bone
00:06:26 – this scale the bottom layer of the skin
00:06:31 – of the dermis scales grow in a tight
00:06:34 – pattern overlapping like shingles on a
00:06:37 – roof each one of these scales pulls off
00:06:40 – and look at the size of that so there's
00:06:43 – a lot of overlap there but not all
00:06:45 – scales are alike the scales on fishes
00:06:49 – are really variable some fishes like
00:06:52 – catfish have no scales at all and then
00:06:55 – there are other fish that look like
00:06:56 – they're wearing a coat of armor what
00:06:59 – this says to us is that evolution is
00:07:01 – acted repeatedly on fish skin depending
00:07:04 – on the ecology of different kinds of
00:07:06 – fishes a fish's environment and the
00:07:09 – predators within it help dictate the
00:07:12 – evolution of its skin and most fish
00:07:16 – scaled or not would evolve another
00:07:18 – strategy for survival one of the things
00:07:21 – that people get all excited about when
00:07:23 – they pick up a fish is how slimy they
00:07:24 – are fish produce mucus the slippery
00:07:28 – mucus rises from the glands and the
00:07:30 – dermis and keeps the fish free from
00:07:32 – clinging parasites it helps to quickly
00:07:35 – heal wounds sometimes contains toxins to
00:07:38 – discourage predators and even may help
00:07:41 – the fish swim faster by reducing
00:07:43 – turbulence
00:07:44 – for the fish slime is good
00:07:47 – the basic fish skin system of epidermis
00:07:51 – and dermis plus the coating of mucus and
00:07:53 – often scales once evolved worked so well
00:07:57 – that it remains in place to this day
00:08:00 – after over 200 million years of
00:08:03 – evolution descendants of the first fish
00:08:05 – ventured up on land and found fewer
00:08:08 – predators and plentiful food but this
00:08:11 – new environment was harsh if they were
00:08:14 – to survive here they would have to
00:08:16 – evolve a far tougher skin when you're
00:08:20 – living in an aquatic watery environment
00:08:22 – skin can be a little bit more giving
00:08:25 – many who come up onto land you've got
00:08:27 – some room major things you got to
00:08:29 – overcome throughout the history of the
00:08:31 – vertebrates skin has always had the
00:08:33 – basic function that it keeps the
00:08:35 – internal environment constant even
00:08:36 – though there are changes outside the
00:08:38 – animal but when vertebrates came up on
00:08:39 – land there was a new requirement on skin
00:08:42 – and that was to avoid drying out and so
00:08:46 – the skin that fish have isn't sufficient
00:08:48 – we went from skin that was wet all the
00:08:51 – time the skin that had to be dry
00:08:54 – land held promise if skin could evolve
00:09:01 – 360 million years ago and smooth-skinned
00:09:04 – tetrapods crawled out of the sea onto
00:09:07 – land these four land creatures evolved
00:09:11 – from scaleless fish they would be the
00:09:14 – common ancestor of all reptiles
00:09:16 – amphibians birds and mammals their
00:09:21 – transition to life on land would not
00:09:23 – have been possible without the evolution
00:09:25 – of new adaptations to their skin you're
00:09:31 – going to remember first they came from
00:09:33 – aquatic environment land is rough and
00:09:36 – dry and the first of these four-legged
00:09:38 – creatures had thin highly permeable skin
00:09:41 – they could not survive long as they
00:09:44 – crawled across solid ground it was skin
00:09:47 – which had to be kept moist which meant
00:09:50 – the animals had to return to water
00:09:51 – regularly if it dried out the animal
00:09:54 – would die as some animals spend more
00:09:56 – time out of the water they evolved a
00:09:58 – tougher outer layer a protein long
00:10:01 – present and fish skin would supply it
00:10:03 – it's called keratin keratin was the
00:10:07 – absolute key to success the key
00:10:10 – innovation that made life on land
00:10:13 – possible and versatile anthropologist
00:10:17 – Nina Jablonski studies skin
00:10:21 – keratin is one of these wonderful
00:10:23 – molecules in evolution that is used over
00:10:26 – and over and over again in different
00:10:27 – places our hair is made of keratin nails
00:10:31 – are made of keratin the claws of other
00:10:35 – animals including birds are made of
00:10:37 – keratin keratin is found in the horn of
00:10:42 – the rhinoceros and in the hooves of whom
00:10:45 – mammals it's all over the places
00:10:48 – keratin grows in dense packs of cells
00:10:51 – and it toughen the skin surface keratin
00:10:55 – is skins moldable plastic depending on
00:10:58 – how it combines with other elements it
00:11:01 – can appear in many forms it can be soft
00:11:03 – like plastic wrap or hard like plastic
00:11:06 – cups but it always provides a durable
00:11:09 – barrier this is the amazing thing about
00:11:13 – evolution is that you can take a very
00:11:16 – basic kind of structure and tweak it a
00:11:18 – little bit here and tweak it a little
00:11:20 – bit there
00:11:20 – to have it serve different functions
00:11:23 – scientists think that keratin first
00:11:25 – appeared in the skin of amphibians in
00:11:27 – places where it was most needed like the
00:11:30 – foot pad where rubbing and abrasion were
00:11:33 – most likely to occur
00:11:35 – [Music]
00:11:37 – when reptiles evolved their keratin
00:11:41 – morphed further gradually it spread
00:11:44 – across the entire reptile skin providing
00:11:47 – increased protection and better survival
00:11:51 – armed with hides full of keratin the age
00:11:54 – of reptiles was on excellent
00:12:01 – physiological ecologist Bill Lutter
00:12:03 – Schmitz studies reptile anatomy
00:12:06 – specifically snakes with melissa miller
00:12:09 – reptiles have evolutionarily changed
00:12:12 – their scan to be much more of a barrier
00:12:15 – to the environment reptiles evolved
00:12:18 – scales to help them cope with an
00:12:20 – abrasive terrain scales are really
00:12:23 – modified little appendages of skin fish
00:12:28 – scales anchored in the dermis were well
00:12:31 – suited to swimming but on rough land
00:12:34 – they would tear out
00:12:37 – [Music]
00:12:39 – amazingly reptiles developed scales that
00:12:42 – anchored onto each other at the surface
00:12:45 – connected as tightly as the pieces of a
00:12:48 – jigsaw puzzle if we look at scales in a
00:12:52 – typical reptile what we see is that the
00:12:55 – the skin layers are just sort of folded
00:12:58 – into this funny beautiful little pleat
00:13:01 – on the surface and there's another
00:13:03 – benefit to this new scaly skin it
00:13:06 – imparts tremendous mobility so that an
00:13:10 – animal that has scales can be extremely
00:13:13 – mobile as well as have very abrasion
00:13:16 – resistant skin and a mobile snake is a
00:13:19 – deadly snake that can also flee its
00:13:22 – enemies but reptiles face another enemy
00:13:27 – on land the Blazing Sun even a single
00:13:31 – crack and the tough keratin scales
00:13:33 – exposes the animals cold-blooded
00:13:35 – interior to dry heat evaporation and
00:13:38 – death
00:13:40 – and in order for reptiles to leave a
00:13:45 – fully aquatic environment they needed to
00:13:48 – have evolved the skin that was mud less
00:13:51 – permeable to water so what is the secret
00:13:56 – ingredient that keeps snake skin super
00:13:58 – tight to find the answer
00:14:00 – Melissa Miller focuses on two very
00:14:02 – similar and very poisonous snakes that
00:14:05 – have natural habitats close to one
00:14:07 – another but yet adopt different
00:14:09 – lifestyles the land-loving Copperhead
00:14:13 – and the semi aquatic cottonmouth we feel
00:14:17 – that some of their differences in
00:14:19 – habitat selection may be tied to the
00:14:21 – physiology of their skin when the
00:14:24 – cottonmouth ancestors went back into the
00:14:27 – water they may have lost some of the
00:14:29 – adaptations in their skin by comparing
00:14:31 – two different snake skins Miller hopes
00:14:34 – to reveal the key ingredient that's
00:14:36 – allowed some reptiles to have watertight
00:14:38 – skin and enable them to live away from
00:14:40 – the water snakes famously shed their
00:14:44 – skin the scales are so tightly
00:14:47 – interlocked that they allow no room for
00:14:49 – growth and they break down from wear and
00:14:52 – tear so four to eight times a month a
00:14:55 – snake will loosen the worn-out layer at
00:14:58 – one end often by rubbing against a rock
00:15:00 – and crawl straight out of it much like
00:15:03 – taking off a sock back in the lab Lutter
00:15:08 – schmidt and miller want to compare how
00:15:10 – waterproof the two snake skin sheds are
00:15:12 – in Melissa's experiments she takes shed
00:15:16 – scans and looks at the amount of water
00:15:18 – that is lost through those sheds over
00:15:21 – time the test is simple they place the
00:15:25 – sheds over test tubes filled with water
00:15:29 – after a week the land-based
00:15:31 – copperhead skin keeps almost all the
00:15:34 – water and a water-loving cottonmouth has
00:15:37 – lost most of his the Copperhead has a
00:15:41 – less permeable skin as you can see
00:15:43 – there's more water left in the sample
00:15:45 – there sheds have roughly equal amounts
00:15:48 – of skin Tite keratin so what is it that
00:15:51 – makes the Copperhead so water proof it
00:15:54 – is a liquid fat called a lipid these
00:15:59 – lipids are extremely important because
00:16:02 – they provide natural water resistance
00:16:06 – water repellent lipids are a key
00:16:09 – component in skins evolution in reptiles
00:16:12 – it seals any cracks between scales
00:16:14 – forming a sun proof seal these animals
00:16:19 – would then dare venture freely over land
00:16:21 – without fear of drying out it gave them
00:16:24 – the tenacity to push further inland and
00:16:26 – dominate the earth just like having a
00:16:29 – raincoat up it has a really good water
00:16:31 – repellent surface the lipids in the
00:16:34 – keratin work together on the very
00:16:37 – surface of the skin to create a tight
00:16:40 – water-resistant layer the Copperhead has
00:16:43 – much more lipids than the cotton mouse
00:16:44 – which is why it can inhabit a more arid
00:16:47 – land based area lipids seem to serve a
00:16:51 – major role in the amount of terrestrial
00:16:53 – behavior we see in many reptiles the
00:16:56 – combination of keratin and lipids set
00:16:58 – the pattern for the reptiles success
00:17:03 – this was important because it allowed
00:17:05 – them to spend much much more time on
00:17:07 – land and it allowed them to get away
00:17:09 – from the water and move into
00:17:10 – environments that before weren't
00:17:11 – available with the right ingredients
00:17:14 – evolution has provided reptiles with
00:17:17 – tough water resistant skin these
00:17:19 – reptiles dared to roam freely across all
00:17:22 – of Pangaea the one supercontinent on
00:17:25 – Earth and as Pangaea splits apart over
00:17:28 – millions of years their skin evolves
00:17:30 – further adapting to changing
00:17:33 – environments their descendants the
00:17:36 – mighty dinosaurs would be the dominant
00:17:38 – vertebrates for a hundred and sixty
00:17:40 – million years
00:17:42 – dinosaurs were a really successful group
00:17:45 – that radiated diversified evolved into
00:17:47 – many many different forms is it possible
00:17:50 – that the secrets of dinosaur domination
00:17:53 – lie in its skin we now know that
00:17:57 – dinosaurs dominated life on Earth for a
00:17:59 – hundred and sixty million years
00:18:03 – their skin the barrier between these
00:18:06 – huge land animals in their environment
00:18:08 – had to play a major role in their
00:18:11 – success but it has been hard to study
00:18:16 – we're used to finding the bones of
00:18:18 – dinosaurs soft tissues are much rarer on
00:18:22 – your left with what effectively is an
00:18:25 – echo and that is what we're usually left
00:18:27 – with could study the dinosaurs because
00:18:32 – soft tissue doesn't last scientists
00:18:34 – usually have to rely on the information
00:18:36 – they can extract from the bones to tell
00:18:38 – them about the skin and the bones do
00:18:42 – have stories to tell in them lies
00:18:45 – evidence that in the age of dinosaurs
00:18:47 – what was needed for survival was armored
00:18:50 – for defense weaponry for predation and
00:18:54 – enough protection to survive long
00:18:56 – distance travel we see huge variations
00:18:59 – from one species of Barnesville to
00:19:01 – another and skin is where these major
00:19:04 – adaptations for survival occur
00:19:07 – megasaurus was a plant-eating dinosaur
00:19:09 – and we know that from a very small teeth
00:19:11 – that it had paleontologist ken carpenter
00:19:14 – excavated the most complete Degas or
00:19:17 – skeleton ever found in 1992 these plates
00:19:21 – are very large triangular structures and
00:19:23 – they were covered with skin these Tufts
00:19:26 – dirty plates were defensive armor
00:19:28 – evolved as deterrent to meat-eating
00:19:31 – predators we think that Allosaurus may
00:19:33 – have in fact been the top predator for
00:19:35 – Stegosaurus we know that because of the
00:19:38 – evidence that we find of tooth marks on
00:19:39 – Stegosaurus bones we also have evidence
00:19:43 – that Stegosaurus did defend itself
00:19:44 – against the Allosaurus because we have
00:19:46 – Allosaurus bones that show punctures
00:19:48 – from the spike of the Stegosaurus the
00:19:51 – Stegosaurus his tail spike was an early
00:19:54 – proof of the modern adage of
00:19:56 – defense is a good offense these hard
00:20:00 – structures found on the outside of
00:20:02 – plant-eating dinosaurs are heavy out
00:20:04 – gross of skin made of the dense protein
00:20:07 – keratin just like with reptiles the
00:20:11 – keratin on its skin would help it ensure
00:20:13 – its survival over time this tough skin
00:20:16 – is reinforced by bone that grows right
00:20:19 – in the skin nature's innovation called
00:20:22 – ossification
00:20:24 – this spike actually formed within the
00:20:27 – skin it was probably covered by a
00:20:30 – material much like our fingernail
00:20:31 – [Music]
00:20:32 – ossification can still be seen today in
00:20:35 – the tough skin of alligators and
00:20:38 – crocodiles some of the closest living
00:20:40 – relatives of the dinosaurs something
00:20:44 – like an old crocodile has bony plates
00:20:47 – away over a centimeter thick covering
00:20:50 – most of its body and these plates in
00:20:52 – turn are covered with protective keratin
00:20:55 – so they are really tough customers
00:20:58 – but skins evolution wasn't always about
00:21:01 – getting tough
00:21:02 – something soft was evolving on the skin
00:21:05 – of some dinosaurs feathers feathers have
00:21:09 – a single shaft from which radiate
00:21:13 – filaments of keratin this is
00:21:16 – Sinosauropteryx which shows a furry down
00:21:19 – of simple feathers because of the
00:21:22 – simplicity of these early feathers
00:21:24 – scientists believe they evolved not for
00:21:27 – flight but as insulation
00:21:29 – feathers evolved as a as a skin
00:21:31 – structure possibly as is the case for
00:21:34 – fur for insulation in small
00:21:36 – ground-dwelling predatory dinosaurs
00:21:39 – fossils have revealed the dinosaurs
00:21:41 – armor and shown evidence of the first
00:21:44 – feathers on earth but in 2007
00:21:48 – paleontologist Phil Manning was invited
00:21:51 – to study an incredible Triceratops
00:21:53 – fossil found in Wyoming I was contacted
00:21:56 – by a paleontologist Peter Larson who
00:21:58 – discovered a triceratops we know that
00:22:01 – this particular fossil is of a
00:22:03 – triceratops because we have the
00:22:05 – beautiful three horns skull of one end
00:22:07 – of the fossil
00:22:09 – Triceratops was the largest of the horn
00:22:11 – dinosaurs measuring approximately 25
00:22:15 – feet long and a whopping 10 feet in
00:22:17 – height
00:22:18 – what made this find so special was
00:22:21 – something that had never been seen
00:22:22 – before dinosaur skin and it was only
00:22:26 – when they started removing large tracks
00:22:28 – of the sandstone which was encasing this
00:22:30 – beautiful fossil that they discovered
00:22:32 – these large tracks of skin impressions
00:22:35 – or what might have actual skin preserved
00:22:37 – on this amazing possum
00:22:39 – Manning's excitement about this finds
00:22:42 – importance is palpable
00:22:44 – it's not like finding a few disjointed
00:22:46 – sentences which are hard to piece
00:22:47 – together to work out what they actually
00:22:48 – mean here we've got a full-blown
00:22:50 – paragraph if not a whole chapter which
00:22:53 – we can gently thumb through and
00:22:55 – understand so much about this particular
00:22:57 – animals skin
00:22:58 – [Music]
00:23:02 – powering up the electron microscope
00:23:04 – Manning is about to take his first step
00:23:07 – toward cracking the skin samples code
00:23:11 – the view is an unprecedented trip back
00:23:15 – through time
00:23:16 – [Music]
00:23:18 – what are actually looking at on the
00:23:20 – screen here is the surface of our hasta
00:23:23 – lion skin that's beautiful you're
00:23:27 – looking at the surface of some
00:23:28 – triceratops skin that's a little over 65
00:23:31 – million years old and that no one's ever
00:23:33 – looked at in this resolution before this
00:23:35 – microscope allows Manning to see what
00:23:37 – elements are present in the fossil why
00:23:40 – we haven't got elements identified I can
00:23:42 – actually use the software in this
00:23:44 – machine to help identify the specific
00:23:45 – element we've got silica oxygen carbon
00:23:50 – is present that could be some of the
00:23:51 – planter lines that we find within this
00:23:53 – environment some of the elements present
00:23:56 – in the skin fossils suggest some
00:23:58 – tantalizing ideas manganese I like
00:24:02 – manganese manganese is important
00:24:03 – elevated manganese levels may indicate
00:24:06 – that the skin was fossilized in colder
00:24:08 – than expected conditions as the clues
00:24:11 – are pieced together a new window into
00:24:13 – the Cretaceous environment begins to
00:24:15 – emerge but the biggest surprise is on
00:24:19 – the outside of the animal they discover
00:24:21 – an enormous variety in the size shape
00:24:24 – and texture of the scales on the skin
00:24:27 – and on small scales these are quite
00:24:30 – robust tough looking scales a new clear
00:24:33 – picture of Triceratops comes into focus
00:24:36 – now looking at the types of scales that
00:24:39 – we see on the skin on this particular
00:24:41 – Triceratops indicates that it didn't
00:24:44 – have a soft spot on its backside Manning
00:24:47 – finds tough scales that would protect
00:24:49 – this creature from its harsh environment
00:24:51 – but surprisingly there is no bony
00:24:53 – ossification this animal would have
00:24:56 – little defense against a t-rex bite
00:25:01 – Triceratops lived toward the end of the
00:25:03 – dinosaurs incredible 160 million year
00:25:06 – reign on earth scurrying beneath the
00:25:10 – beasts lumbering feet were a different
00:25:12 – kind of animal
00:25:14 – warm-blooded mammals whose adaptive skin
00:25:17 – would change in ways that would allow
00:25:19 – them to grow and dominate the world as
00:25:22 – the dinosaurs had before them mammals
00:25:28 – live for a hundred and sixty million
00:25:30 – years in the shadow of the dinosaurs
00:25:32 – they remained small and out of the way
00:25:35 – for a long time what with the dinosaurs
00:25:38 – gone there is new opportunity and
00:25:40 – hundreds of new species evolved and two
00:25:44 – amazing adaptations and skin ensure
00:25:47 – their survival almost anywhere mammalian
00:25:50 – skin is different again from reptilian
00:25:53 – skin because mammals differ
00:25:56 – fundamentally in their physiological
00:25:58 – properties
00:26:00 – this physiological difference rests in
00:26:03 – the way the bodies regulate their
00:26:04 – temperatures reptiles are cold-blooded
00:26:08 – so their body temperature depends on
00:26:11 – their surroundings when it is cold their
00:26:14 – body temperature dips it becomes slow
00:26:16 – and sluggish when it's warm their body
00:26:19 – temperature rises they are more active
00:26:23 – mammals on the other hand are
00:26:24 – warm-blooded they maintain their own
00:26:27 – constant body temperature this gives
00:26:30 – them an advantage in a climate with
00:26:32 – seasonal changes in extremes of hot and
00:26:34 – cold but it also presents a challenge
00:26:37 – because in the cold warm-blooded mammals
00:26:40 – like us and freeze to death as with the
00:26:44 – reptiles before mammalian skin responds
00:26:47 – accordingly the skin of mammals has
00:26:51 – evolved over several million years to
00:26:54 – have certain properties including
00:26:57 – marvelous outgrowths called hairs that
00:27:01 – protect the surface of the mammal and
00:27:03 – provide tremendous amounts of insulation
00:27:07 – hair also guards against rubbing and
00:27:10 – abrasion providing a lot of protection
00:27:12 – against routine wear and tear so some
00:27:16 – animals running through the forest or
00:27:17 – rolling on the grass or on the ground
00:27:19 – it is completely protected the ancestors
00:27:24 – of mammals sprawling reptilian creatures
00:27:26 – called synapsids probably already had
00:27:29 – evolved hair
00:27:31 – it is thought that hair began as a
00:27:34 – mutation on the skin sprouting up in
00:27:36 – small spaces between the scales of
00:27:39 – creatures like weeds in a brick path a
00:27:42 – [Music]
00:27:43 – close-up look at a contemporary human
00:27:46 – hair reveals that while hair appears
00:27:48 – smooth it's actually scaly just like a
00:27:51 – reptile scale it's why our hair can
00:27:54 – tease up and be tangled into a mess and
00:27:57 – why it lies flat when combed in line
00:28:00 – with the scales bias hair is formed in
00:28:05 – the lower dermal layer of skin and can
00:28:07 – easily regenerate mammals evolved a
00:28:12 – unique kind of skin one that boosted its
00:28:15 – chances of survival
00:28:18 – they now have a head start in exploring
00:28:21 – new terrains because their insulation
00:28:23 – enables them to travel long distances
00:28:25 – and adapt to different climates
00:28:30 – but it's not just about staying warm in
00:28:34 – some climate it's about keeping cool the
00:28:39 – elephants tough skin and large barrel
00:28:41 – shaped body retains a lot of heat in the
00:28:45 – course of evolution the ancestors of
00:28:48 – elephants living in tropical
00:28:50 – environments really had to face the
00:28:53 – challenge of how to keep cool the
00:28:57 – elephant skin evolved to enable a
00:28:59 – process that works just like a car's
00:29:02 – engine cooling system to beat the heat
00:29:05 – elephant ears like two living car
00:29:08 – radiators our build thin stretched over
00:29:11 – cartilage packed full of blood vessels
00:29:13 – and just like coolant arriving hot from
00:29:17 – the engine hot blood circulates from the
00:29:20 – elephant's body into its ears where it
00:29:23 – is cooled by its proximity to the open
00:29:25 – air ear flapping kicks up a breeze and
00:29:28 – boosts the cooling effect like a
00:29:30 – radiators fan and the elephant's blood
00:29:34 – cooled by up to 10 degrees is kept from
00:29:36 – overheating in the blistering Sun
00:29:39 – [Music]
00:29:41 – frequent baths of water and mud help to
00:29:47 – with heating and cooling systems in
00:29:49 – place mammals are able to spread out
00:29:52 – over all seven continents but this isn't
00:29:56 – the only secret to the mammal success
00:29:59 – skin and females goes through another
00:30:01 – remarkable transformation without skin
00:30:05 – we wouldn't have had mammary glands
00:30:07 – female mammals developed the ability to
00:30:10 – lactate passing nutrition to their young
00:30:13 – through skin hey buddy
00:30:18 – biologist Katherine Heim studies
00:30:20 – lactation in its role in survival and
00:30:23 – behavior in a managed population of
00:30:25 – rhesus macaques on Cayo Santiago Island
00:30:28 – in Puerto Rico rhesus macaque like the
00:30:32 – ones on Cayo Santiago typically nurse
00:30:34 – from 6 months up to about a year
00:30:38 – mother's milk delivered through the
00:30:40 – mammary gland greatly improves the
00:30:43 – chances of a baby's survival by
00:30:45 – providing nutrients and antibodies that
00:30:48 – protect against diseases the
00:30:52 – evolutionary roots of breastfeeding go
00:30:54 – back over 300 million years to the time
00:30:57 – of the strange reptilian creatures
00:30:59 – called synapsids ancestors of mammals
00:31:02 – and us who laid eggs rather than carried
00:31:06 – their young
00:31:07 – synapses 310 million years ago evolved a
00:31:12 – mechanism for expressing fluids through
00:31:15 – their sweat glands that kept eggs moist
00:31:18 – over subsequent millennia the fluid that
00:31:21 – simply dripped from the skin like sweat
00:31:24 – grew richer and richer in nutrients
00:31:27 – today there are only three species of
00:31:30 – egg-laying mammals called monotremes the
00:31:35 – best known is the platypus which like
00:31:38 – the synapsids lactates through pores in
00:31:41 – the skin the skin has turned sweat into
00:31:45 – food the fact that modified sweat glands
00:31:51 – turn out to be milk producing glands
00:31:55 – that actually feed mammalian young this
00:31:58 – is a superb example of evolution in
00:32:01 – another lineage of mammals mammals milk
00:32:05 – grew richer the delivery system more
00:32:07 – elaborate until the familiar and
00:32:10 – successful combination of nutritious
00:32:12 – milk b****** and nipples was in place in
00:32:15 – almost every female mammal
00:32:20 – [Music]
00:32:25 – why do males have nipples they develop
00:32:29 – in the embryo before gender is
00:32:31 – determined and remain ever after male
00:32:35 – nipples may be a useless adaptation but
00:32:39 – for mammals the female breast remains
00:32:42 – vital for survival
00:32:44 – the most important aspect of maternal
00:32:47 – care is lactation and Kathryn hind has
00:32:50 – learned that macaques used the time they
00:32:52 – are dependent on their mothers to learn
00:32:54 – vital lessons that could make the
00:32:56 – difference between life and death
00:32:58 – mother's milk allows infants to learn
00:33:02 – about the world in which they're going
00:33:04 – to have to be adults while still being
00:33:06 – energetically protected by their mother
00:33:08 – so while they get milk they're able to
00:33:10 – learn how to process food learn how to
00:33:13 – socially interact and develop all the
00:33:16 – skills that they'll need in a
00:33:17 – complicated a**** world the
00:33:20 – socialization encouraged by skin's
00:33:22 – evolution of breast would blossom with
00:33:25 – the mammals that emerged close to 2
00:33:27 – million years ago human beings but
00:33:32 – humans did not retain skin like macaques
00:33:34 – a new kind of skinny volved unique among
00:33:38 – primates humans have really different
00:33:40 – skin from any other creature all of a
00:33:43 – sudden we have a very different kind of
00:33:46 – animal in Equatorial Africa not an ape
00:33:49 – sitting or or scurrying around near the
00:33:53 – shelter of trees but an active striding
00:33:56 – biped spending a lot of its time in open
00:33:59 – hot environments the Lions coat the
00:34:05 – gorillas fur none of it would be of use
00:34:08 – to humans we needed to get naked
00:34:11 – and we needed to keep cool humans were
00:34:15 – on the run out of Africa and straight to
00:34:19 – the top of the food chain scientists now
00:34:22 – believe that what made it possible was a
00:34:24 – single evolutionary mutation in human
00:34:27 – skin
00:34:29 – how did humans come to dominate all
00:34:32 – other mammals could the answer lie in
00:34:35 – the way the human skin evolves Jim is a
00:34:38 – really different skin from any other
00:34:40 – creature human skin is of course a
00:34:43 – barrier to the outside world it protects
00:34:46 – our insides and is by far the largest
00:34:48 – organ in the human body it is
00:34:51 – responsible for 1/6 of our body weight
00:34:54 – in other words if a hundred and sixty
00:34:56 – pound man were able to step out of his
00:34:58 – skin he would lose more than 26 pounds
00:35:01 – it's hard to find important function in
00:35:04 – the body that skin doesn't have a role
00:35:05 – in human skin like all skin of animals
00:35:09 – with spines is made up of two
00:35:11 – distinctive layers the top one replacing
00:35:14 – itself completely over the course of 28
00:35:17 – days shedding half a million cells an
00:35:19 – hour this churning mix of dead and live
00:35:23 – cells seals out water dust and germs it
00:35:27 – is a very very specialized unusual organ
00:35:31 – that is simple but deceptively complex
00:35:35 – Dan Lieberman is a professor of
00:35:38 – biological anthropology at Harvard
00:35:40 – University I studied the evolution of
00:35:42 – the human body I'm interested in why the
00:35:44 – body looks the way it does and how it
00:35:46 – got to be that way humans are most
00:35:49 – closely related to chimpanzees we know
00:35:51 – that the human in the chimpanzee
00:35:53 – lineages diverged sometime around 6 to 7
00:35:55 – million years ago the last common
00:35:58 – ancestors to chimps and humans hominids
00:36:00 – lived in the tropical climates of Africa
00:36:03 – they looked like chimpanzees walking on
00:36:06 – all fours and covered in hair sometime
00:36:09 – around 6 million years ago hominids got
00:36:12 – up on two feet and became bipedal and
00:36:14 – for millions of years the earliest
00:36:16 – hominids were
00:36:18 – bipedal chimps in a way being able to
00:36:21 – stand upright and walk is only part of
00:36:23 – the human evolution story as humans
00:36:26 – begin spreading out across continents
00:36:28 – something else proves to be critical in
00:36:31 – the quest for domination the ability to
00:36:33 – run the human lineage became more active
00:36:38 – and they increased in stature in their
00:36:42 – levels of activity different
00:36:45 – physiological needs became apparent but
00:36:50 – what enables humans to be able to run in
00:36:52 – the first place the answer lies with
00:36:57 – skin Dan Lieberman and his team at
00:37:01 – Harvard examined why and how human
00:37:03 – beings evolved to run and they believe
00:37:06 – the evolution of our skin played a big
00:37:08 – role in that change Lieberman and his
00:37:11 – team demonstrated at least 27 anatomical
00:37:15 – features on the human body evolved
00:37:17 – solely for running to them that is clear
00:37:21 – evidence that running is an extremely
00:37:23 – important part of what gave humans a big
00:37:25 – advantage most pronounced among these
00:37:29 – features our large gluteus maximus
00:37:32 – better known as the but humans have an
00:37:36 – enormous gluteus maximus the largest
00:37:39 – muscle in the human body you were to
00:37:41 – look at a chimpanzees rear end you'd see
00:37:42 – it was very small very very pathetic
00:37:44 – so I'm ready I'm recording when our
00:37:48 – subject was on the treadmill walking he
00:37:49 – saw that not much is happening or she's
00:37:51 – not really sweating very much and her
00:37:53 – Kirk on conspiracy stable and her
00:37:56 – gluteus maximus isn't firing very much
00:37:58 – but when she starts running she's
00:38:00 – falling every time she hits the ground
00:38:02 – her body wants to fall forward they're
00:38:04 – going to gluteus maximize the powerful
00:38:08 – glutes kick into gear when we run to
00:38:10 – keep us from falling over
00:38:11 – stabilizing the trunk and legs for four
00:38:16 – million years the ancestors of humans
00:38:18 – walked on two legs and yet they didn't
00:38:21 – advance much beyond being bipedal Apes
00:38:25 – so walking is not what transforms the
00:38:28 – hominid body but according to Lieberman
00:38:31 – running could be it's still a mystery of
00:38:34 – course as to why humans became furless
00:38:36 – sweaty why we became naked but we think
00:38:39 – at least I think that it happened
00:38:41 – because of of thermoregulation and
00:38:44 – running evolving features to run is not
00:38:47 – enough the hominid body needed something
00:38:50 – else a cooling system mammal skin had
00:38:55 – evolved hair to keep them warm in cold
00:38:57 – climates early hominids in Africa have
00:39:01 – the opposite problem they need to be
00:39:03 – able to keep their bodies and brains
00:39:05 – from overheating
00:39:07 – ever able to adapt the skin of humans
00:39:10 – and other mammals living in hot climates
00:39:12 – simply stop producing so much hair we
00:39:15 – have compared to other mammals
00:39:18 – particularly we have skin that is got
00:39:21 – almost no hair human skin would evolve
00:39:24 – to supply its own cooling bath in the
00:39:27 – form of sweat sweating was essential in
00:39:31 – the progress of human evolution because
00:39:34 – it helped us maintain cool brains the
00:39:39 – primate brain if you heat it up even a
00:39:41 – few degrees Celsius above normal it
00:39:44 – can't function properly so how do you
00:39:47 – keep a primate brain cool you basically
00:39:50 – sweat mammals had long had sweat glands
00:39:55 – called apocrine glands that produce an
00:39:58 – oily liquid what causes a horse to
00:40:02 – lather or a pig to look sweaty it's this
00:40:05 – primitive sweat that creates our
00:40:07 – distinctive human body odor but sometime
00:40:11 – close to two and a half million years
00:40:13 – ago human skin began to produce a whole
00:40:16 – new kind of sweat composed almost
00:40:18 – entirely of pure cooling water the water
00:40:23 – came from a new kind of skin gland
00:40:27 – the egg cream gland chimps and some
00:40:30 – other mammals do have eccrine glands but
00:40:33 – only a few human skin has millions
00:40:37 – Lieberman thinks this stunning explosion
00:40:40 – of cooling sweat glands and humans made
00:40:43 – them better hunters my bet is that what
00:40:45 – happened is that the hominids at some
00:40:47 – point started being more fur less and
00:40:50 – started sweating and then that enabled
00:40:52 – early hominids to hunt and run down
00:40:55 – animals
00:40:55 – how did running and sweating give the
00:40:58 – human hunter such an advantage we need
00:41:01 – to think of the differences between
00:41:02 – panting and sweating an animal cools
00:41:05 – down by panting whereby it breathes
00:41:08 – shallowly over its tongue which is
00:41:10 – filled with blood vessels the blood gets
00:41:13 – cooled and sent back into the head and
00:41:15 – body of the animal compared to sweating
00:41:18 – it is highly inefficient so that means
00:41:21 – that in the middle of the day they tend
00:41:22 – to seek the shade particularly hot
00:41:24 – places like Africa they can also only
00:41:27 – pan while trotting which means that an
00:41:29 – animal cannot cool down when it is
00:41:31 – galloping so if a human hunter two
00:41:34 – million years ago can make an animal run
00:41:36 – at a gallop within 10 to 15 minutes that
00:41:40 – animal will go into hyperthermia tense
00:41:44 – and because it can't sweat it gets too
00:41:47 – hot and that will eventually kill the
00:41:48 – animal most humans can run at a speed
00:41:52 – that is faster than the trot to gallop
00:41:54 – transition so our early ancestors may
00:41:57 – have hunted by tracking an animal for
00:41:59 – miles
00:42:00 – the first marathoners they could force
00:42:03 – the animal to gallop for long distances
00:42:05 – causing it to overheat in the blistering
00:42:08 – Sun
00:42:09 – so the key adaptation for humans to
00:42:12 – enable us to do this persistent hunting
00:42:14 – is our skin it's the ability to sweat
00:42:17 – and cool down by mechanism other than
00:42:20 – tenting the ability to sweat may have
00:42:22 – allowed humans to become the most
00:42:24 – successful and dominant predators on the
00:42:26 – planet now free to spread across the
00:42:31 – world humans found once again their skin
00:42:35 – adapting to changing conditions human
00:42:38 – skin doesn't come in just one color it
00:42:41 – comes in a whole spectrum of colors from
00:42:44 – the very darkest near ebony color to the
00:42:47 – very lightest near ivory color this
00:42:50 – beautiful sepia rainbow of colors
00:42:54 – evolved as a product of natural
00:42:56 – selection
00:42:58 – [Music]
00:43:00 – humans are remarkable because they have
00:43:02 – a wide variety of skin colors peoples
00:43:05 – that live in very fun rich environments
00:43:07 – tend to have a lot of melanin there in
00:43:09 – their skin because mountian helps
00:43:11 – protect from damage by the Sun by
00:43:14 – contrast people that live in very Sun
00:43:18 – poor environments tend had very little
00:43:20 – felon with the result that they have
00:43:22 – fairly light skin it's controversial how
00:43:25 – much of human skin is adaptive versus
00:43:27 – how much is simply serendipitous as a
00:43:29 – result of chance
00:43:33 – today the environment is changing at a
00:43:36 – rapid rate as it has done many times
00:43:38 – before animals all over the world
00:43:42 – including us will have to adapt or die
00:43:45 – no one knows whether skin will be up to
00:43:48 – the challenge one more time right now
00:43:52 – animals living on the surface of the
00:43:53 – earth are undergoing unprecedented
00:43:56 – environmental challenges not only from
00:43:59 – global warming but also because of a
00:44:03 – slow erosion of the ozone layer
00:44:08 – some animals can't even tolerate where
00:44:11 – they live and they have to move to
00:44:12 – cooler places so there is evolution of
00:44:17 – the skin occurring in these lineages
00:44:20 – that are being subjected to new
00:44:22 – evolutionary forces but we don't know
00:44:25 – exactly what course this evolution will
00:44:27 – take evolution happens over time and any
00:44:33 – adaptive changes to skin may not emerge
00:44:36 – for hundreds or thousands of years but
00:44:40 – if 400 million years of success is any
00:44:43 – guide the organ we call skin will evolve
00:44:47 – [Music]

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