BBC Secrets of Bones s01e05 Episode Script

Bones.
They offer structure, support and strength, but they have a much bigger story to tell.
Vertebrates may look very different on the outside, but one crucial thing unites them all.
The skeleton.
I'm Ben Garrod, an evolutionary biologist with a very unusual passion.
This is unbelievable! There are too many skeletons for me to look at all at once.
As a child I was fascinated by bones.
Now, skeletons have become my life.
And I put them together for museums and universities all over the world.
I'm going to explore the natural world from the inside out.
To see how the skeleton has enabled animals to move .
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hunt and even sense the world.
I will take you on a very personal journey, to discover how this one bony blueprint has shaped such massive diversity across the animal kingdom, and how it has come to dominate life on Planet Earth.
This time, we'll see how bones have helped vertebrates to capture and devour practically every type of food on the planet.
We'll look at extreme jaws bizarre teeth It really is a bonkers adaptation.
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highly specialised bony tools, and one small appendage that has had an immense impact.
It may not look much, but it changed the course of our evolutionary history.
I'm going to reveal the Secrets of Bones.
This is the jaw of the largest living toothed predator on the planet.
At five metres long, it's from a sperm whale that was nearly 30 metres in length.
The teeth can be 20cm long, and they're all roughly the same in terms of their shape.
This makes them perfectly adapted for grabbing and killing.
Now teeth and jaws absolutely fascinate me because they reveal so many of the secrets behind an animal's life and their success.
Sperm whales may have a spectacular set of jaws but there are more than 60,000 species of vertebrate and each has evolved its own special way of feeding.
Jaws first appeared around 420 million years ago.
Important tools for catching and consuming food, their shape and size adapted to exploit whatever was available.
This evolutionary change can take place surprisingly quickly.
To understand the story of rapid jaw evolution, I need to get an MRI scan of my skull.
The information is processed to create a model in plastic.
I'm more than a little curious to see what my own skull looks like.
I've been working with bones for 20 years but this is a first.
I'm quite shocked.
It's so weird to look at your own skull, whilst you're still alive, I think, really.
Even though I study bones, you look in a mirror and you don't see all these little lumps or this massive brow ridge that I apparently have, or this quite large jutting jaw.
Weird! I'm taking my skull to Dr Carolyn Rando, an archaeologist at University College London, who's been conducting some fascinating research into how human jaws are adapting to our ever-changing diet.
You've got an impressive array of skulls here, Carolyn.
What can they tell us about the evolution of our jaws? Well, what we have here is we have a selection of skulls going all the way back from Neanderthal man to Cro-Magnon, and medieval London and post-medieval London here.
And so while these give us a cross section of essentially human evolutionary history, my main interest is with these two here.
What I found out through my research is that jaws have got significantly smaller since the medieval period, up until the modern period.
We're talking just several hundred years, aren't we? Absolutely.
So the medieval period ends in 1550 and post-medieval were talking 17-1800s, 1900s.
When you say the jaws are changing, how? Well, what's happening is that for one, in this individual, we have what we call an edge to edge bite, which means that his front teeth line up perfectly.
so real nice top and bottom together.
And what we have here is his top teeth and bottom teeth, they don't fit together at all.
That's massive, that.
I'm closing mine now, mine do the same.
Is that typical of modern man now? Absolutely.
And in this individual here they fit together so poorly that I can put an entire finger in between his upper and lower teeth.
How would my diet make my jaw become smaller? Throughout human evolution, we've had a very specific type of diet which is lots of rough, hard food.
Tough and fibrous, isn't it? Exactly.
Yeah, we really have to chew hard to make our food work for us, and all of that work is stimulating our jaws to grow.
It stimulates our teeth, which stimulates the jaws, and then the whole face responds in kind to these things.
And so what happened then is we switched from a very traditional agriculturalist diet, to one that was soft and sticky and very sweet, and something that's almost identical to what we have now.
Processed foods, I guess.
Absolutely.
We don't have that same type of interaction between the food and the jaws any more, they just tend to become smaller through inactivity.
Although the trend is towards an increasing overbite, the severity differs between individuals.
And this is largely down to their particular eating habits.
So where does that leave me? Now I have another skull for you.
I just happen to have it in my bag, as I often do.
Now I want to see what you make of this one.
And if it looks familiar, it's because it's mine.
Ah, Ben, that's amazing! It looks just like you.
Thank you! We're very attached.
This is a skull I've had printed off from a 3D image, but where does this fit with the jaw story? Well, if we compare it to our two gentlemen here, what we can see is that while you are not quite as bad as our modern individual over here, you still do have quite a bit of an overbite here.
So I think you're going more towards modern, but not quite as bad as this gentleman here.
It's reassuring.
Can we predict what will happen to humans in the future? Will this carry on, will they get smaller? I think it's a bit hard to say, because who knows what our diet will be like 50 or 100 or 200 years from now.
We could have a liquid-based diet, or maybe something that's pill-based, instead of actually chewing our food, and then I imagine that our jaws would start getting smaller yet again.
I love this, because it really emphasises yet again just how malleable, changeable, adaptable, not only the skull, but bones and skeletons in general really are.
Dr Rando believes that due to the lack of tough, fibrous foods in our diet, there's no longer a need for large, powerful jaws.
This is evolution in action, and it is happening to us.
We are not outside of our environment, we are still evolving and adapting to everything around us.
Diet has shaped the vertebrate jaw.
In some cases, to the extreme.
Snakes' flexible mandibles allow them to consume enormous prey.
Some species can open their jaws 180 degrees, stretching so wide they can eat prey five times larger than their own heads! So just how do they do this? Well, the old idea that they dislocate their jaws, that's a load of rubbish.
What they actually do is far more interesting.
You can see here that each side of the lower jaw is made up of different bones that are connected together, and both lower jaws aren't even attached to one another.
This all goes together to make a very flexible lower jaw and it's connected through a whole network of very tight but elastic-like ligaments.
Imagine that my two arms are the lower jaw bones or mandibles of the snake, and these two elastic bands are the ligaments that hold the jaws together.
When the snake is trying to eat something, these ligaments stretch allowing the jaw bones to spread massively.
This is how a snake can eat something much larger than you might expect.
It's very simple but effective.
Snakes are the ultimate binge eaters.
They're ectothermic, relying on the environment to warm their bodies, and so need to conserve energy wherever possible.
By eating huge meals every few weeks, snakes can maximum food intake whilst minimising energy expenditure.
To achieve this, their bones have had to adapt spectacularly.
Once they've secured their prey, they move one mandible forward at a time to swallow it.
It can then take several days for their food to be dissolved by strong acids in their stomach.
The African egg-eating snake has found a more immediate bony solution to breaking up its prey.
It feed exclusively on bird's eggs.
Its skeletal secret is revealed by this video X-ray.
With a superbly flexible jaw, it can consume an egg many times bigger than its head.
Knife-like bony spikes in its vertebrae protrude into the body cavity.
When the egg reaches the part of the backbone with downward pointing spines, the snake arches and squeezes.
The spikes first pierce the shell and then slit the membrane inside, releasing a highly nutritious meal.
A backbone that can break up your food is an ingenious skeletal adaptation.
But most vertebrates use a more conventional method, teeth.
They're mostly made up of enamel and dentine, and are similar in composition to bone.
But as they contain little or no collagen, they're much harder.
Teeth do different jobs from biting and ripping to crushing and nibbling.
A wide variety of foods has led to a diverse range of tooth shape and size.
Carnivores have particularly impressive teeth.
They use their canines for puncturing, carnassials for shearing and incisors for tearing flesh.
However, it's a herbivore that holds the record when it comes to tooth size.
The animal with the largest teeth on the planet is the elephant.
First up, teeth for chewing.
They're massive! Each one of these molars can be 30cm in length and can weigh up to five kilograms.
Their flattened surface is ideal for grinding.
They're also heavily ridged on the top, and this is a perfect adaptation for a vegetation diet which is really tough and fibrous.
An elephant gets six sets of these teeth throughout its lifetime.
As each one is worn down, new ones are pushed forward from the back of the mouth, a bit like a conveyor belt.
As the last one is worn down and is finally lost, the elephant can no longer eat and this marks the end of the animal's life.
The elephant's biggest teeth are its tusks.
They can grow to more than 3m long.
They're actually modified incisors like the front teeth in humans.
Like ours, they keep growing, as much as 17cm a year.
Made from ivory, a kind of dentine, tusks are important for display and defence, and as tools for helping elephants collect their food.
There's a marine mammal that has independently evolved tusks that aren't used for feeding at all.
The walrus has these enormous tusks.
These are actually specialised canine teeth which erupt from the upper jaw here and these tusks can be over one metre in length.
Their scientific name "odobenus" means "tooth walker.
" And walruses use their teeth to haul their one tonne bodies out of the icy water and on to ice floes.
The tusks are also used for duelling and defence.
If they're not used for eating, how do they feed? Walruses produce jets of water to uncover clams hidden in the silt on the sea bed.
They can consume 6,000 in one feeding session.
Exactly how they were able to prise open the shells puzzled researchers for years.
Looking at the jaws, they noticed that the teeth were very worn.
Now this you might expect from an animal that is eating and chewing and crushing lots of shellfish.
But when scientists looked in the stomachs of walruses, they found they can have up to 70 kilograms of shellfish meat and not a single shell.
What researchers discovered is that walruses are able to turn their mouths into powerful suction devices.
And they do this through some very specific skeletal adaptations.
The first of which is in the roof of the mouth.
Now you can see here it's highly arched and domed, and this allows them to put their thick, muscular tongue right at the front of their mouths.
They grind their jaws together so tightly that this is what wears the teeth down.
So they've got the shellfish at the front of their mouths and lips, their teeth are held together very tightly and this tongue is pushed forward.
They'll pull this back so quickly that it forms a vacuum, and the vacuum power is so strong that it sucks the meat clean out of the shellfish.
In captivity, walruses have been seen to suck a hole through plywood board! Vertebrates have evolved many novel ways of using their mouths to feed.
But there is one specialist feeder with the most bizarre-looking teeth I have ever seen, and a specimen is kept in the stores of Dublin's Natural History Museum.
A close relative of the walrus, it's one of the most abundant large mammals on earth.
It's the crabeater seal.
There are estimated to be 15 million of them found in Antarctic waters.
As they primarily live on free-floating pack ice in remote and inhospitable locations, they are rarely seen and little studied.
Much of their lives still remain a mystery.
The crabeater seal you assume would eat crabs and even the scientific name, "Lobodon carcinophaga," means "lobed tooth crab eater.
" But more than 95% of their diet is made up of Antarctic krill, a shrimp-like crustacean, and they can consume 20 kilograms of them a day! It's said to have the most complex teeth of any carnivore! Like the walrus, the crabeater seal uses suction to feed, but in a very different way.
As it swims, it sucks water and krill into its mouth, then filters the tiny crustaceans through its teeth.
I genuinely love these teeth.
They fit together perfectly.
And by being shaped with all these little lobes and nooks and crannies, the teeth can fit together and form an amazing sieve.
It really is a bonkers adaptation and these teeth are perfectly adapted feeding tools.
Using a mouth to capture and manipulate food works for most vertebrates.
Sometimes, however, jaws and teeth just aren't enough .
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and more sophisticated bony tools are needed to secure a meal.
Particularly when you live in a challenging environment where food can be hard to come by.
The monkfish is one of the ultimate ambush predators.
It's the stuff of nightmares, it really is.
It's more alien than it is animal, and it's one massive killing machine head with a little tail attached to the back of it.
This hefty beast of a fish sits on the sea bed where it's dark and murky for long periods of time.
It has a set of skeletal adaptations that really help maximise any chance of getting some grub.
The most peculiar of which is a lure.
The monkfish is a species of angler fish.
The lures of angler fish come in a variety of cunning shapes to entice prey within jaw's reach.
Some deep sea species even have ones that glow in the dark.
On the monkfish, the lure is a specialised dorsal filament on its head made of bone.
And its success, I think, is almost entirely down to this one little bony appendage.
Now fish are quite inquisitive, so something will swim past, it'll have a good look and then that's the start of the end.
The monkfish has a clever strategy to bring food straight to its mouth.
There are other vertebrates that have evolved even more sophisticated ways to gather food, and the most advanced example of this is in the human body.
It's a bony feature that has totally revolutionised the way we collect our food, and is found in the skeletons of most primates, including this gorilla.
When you compare my hands to those of the gorilla here, you can see they are similar.
Not only the shape of the bones, but the orientation, the number of bones, everything.
But more than that, we share this wonderful, unassuming opposable thumb.
It may not look much but it changed the course of our evolutionary history.
An opposable digit enabled primates to move their thumb freely and independently, giving them a precision grip to grasp branches, pick leaves and use tools to attain food normally out of reach.
Around 3.
5 million years ago, something happened in our evolutionary history that set us apart from our primate cousins.
Primates mainly walk on all fours, but when our early human ancestors started walking upright on two legs, it freed up their hands allowing them to use their opposable thumbs to carry and manipulate tools, including weapons for hunting.
With arms freed up, they became skilled at throwing, helping them hunt big game at a distance, enabled by a set of skeletal adaptations.
The human shoulder has an amazing ability to release stored energy from a huge crisscrossing network of tendons and ligaments right across this area.
It acts like a slingshot and this allows us to be such good throwers.
Today, top class baseball pitchers can throw accurately at speeds of over 100 miles an hour.
There are three key skeletal adaptations, the first of which is having a really high and mobile waist, and this allows a lot of torsion in the torso.
Secondly and really importantly is the very low position of the shoulder blade up on the body.
Our humerus, our upper arm bone here, has the ability to twist and turn, as well.
This all happened about two million years ago, way before we existed as homo sapien, back in the day when homo erectus roamed the earth.
Our ability to throw and our success as hunters is an important part of why we have thrived as a species.
But there's one primate that stands out as having the most highly specialised hands that it uses in an unparalleled way.
This lemur from Madagascar is the world's largest nocturnal primate.
It's the aye-aye.
Feeding on insects and larvae hidden deep inside tree trunks, it needs very specialised digits to extract them.
Now, like most primates, it has this wonderful opposable thumb allowing it to grasp and manipulate objects.
But unique to the aye-aye, it has a very, very specialised finger.
So you can see this wonderful third digit, which is a very long needle-like structure with this great little hook claw on the end.
To try to find where the grubs are hiding, the aye-aye uses its highly sensitive bony finger to sound them out by tapping.
It'll tap up to ten times a second.
Much faster than I can do.
This is called percussive foraging.
The aye-aye uses its large ears to listen for the echo produced from the tapping to locate where the grubs are hiding.
It's the only primate to use echolocation.
Once it's pin-pointed a grub, it gnaws a hole in the wood with its chisel-like teeth and uses its spiky long finger to search for it.
This finger has a ball and socket joint which is unique in the primate world.
Now I've got one in my hip, but nothing else has one in its fingers.
And it gives the aye-aye's finger great flexibility to explore inside wood cavities.
Once it's found the little grub, it'll use its third finger again, drag it out, eat it.
With its sophisticated and specialised hands, the aye-aye is, in my opinion, the most extraordinary predator on Planet Earth! The skeleton has allowed vertebrates to capture and devour practically every type of food on the planet, using a diverse range of jaws, teeth and other sophisticated bony tools.
Next time, I'll be investigating what role bones play in the three crucial things needed for reproduction.
Flirting, fighting and mating.
It's the largest penis bone on earth.