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  • 2 days ago
Secrets of Bones episode 6
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00:00Bones. They offer structure, support, and strength. But they have a much bigger story to tell.
00:22Vertebrates may look very different on the outside, but one crucial thing unites them all.
00:30The skeleton.
00:35I'm Ben Garrett, an evolutionary biologist with a very unusual passion.
00:41This is unbelievable. There are too many skeletons for me to look at all at once.
00:47As a child, I was fascinated by bones.
00:51Now, skeletons have become my life.
00:54And I put them together for museums and universities all over the world.
01:05In this series, I've been exploring the natural world from the inside out.
01:11So far on my journey, we've seen how a single basic body plan has given rise to vertebrates of practically every possible shape and size.
01:24Bones have evolved for running, flying, hunting, and even sensing the world.
01:35But there is one significant and defining power more important than anything else.
01:40And bones have a crucial part to play.
01:43And that is sex.
01:44This time, we'll discover just how important the skeleton is in the race to reproduce.
01:53From courtship...
01:55This skull glows my mind.
01:58It looks like an alien, but there's nothing extraterrestrial about it.
02:01To competition...
02:02When this weight hits the ground, that's approximately the same impact as two bighorn sheep smashing heads together.
02:13And finally, copulation.
02:16It's the largest penis bone on earth.
02:19I'm going to reveal...
02:20The secrets of bones.
02:23Sex has had a dramatic impact on the vertebrate skeleton.
02:42And in the struggle to reproduce, animals have evolved some extreme skeletal adaptations to maximise their genetic success.
02:53To begin, I'm going to look at the lengths vertebrates go to, to stand out in a crowd.
03:05Attraction isn't always about bright colours, big feathers, or some impressive dancing.
03:25It runs bone deep too.
03:28And for many vertebrates, the skull is crucial during courtship.
03:39Take this gorilla skull here, for instance.
03:41It's got this amazing structure on the back of the skull.
03:44Now, this is the sagittal crest.
03:46And when I see one of these, usually, it tells me that there are massive muscle attachments
03:49which go right down the side of the face and to the jaw.
03:53These guys have a very heavy, fibrous diet and need to do what we call industrial processing of their food,
03:59where they chew and chew and chew.
04:02But if this adaptation has evolved purely to help gorillas survive,
04:06you'd expect to find it in both sexes.
04:11Although female gorillas have a practically identical diet,
04:15by comparison, their sagittal crests are much smaller.
04:20It's only in the big, top males you see a crest like this, which is just so prominent.
04:28And I think I know why.
04:31In adult male gorillas, the bony ridge acts as a base for a layer of fatty tissue,
04:38creating a huge crest.
04:42But this isn't just for eating.
04:45It's also for display.
04:47Like a peacock's tail.
04:52Males with bigger crests tend to attract more mates.
04:59It's thought that a large ridge is an indicator of a strong, healthy individual.
05:05In the natural world, females are much more likely to select a male
05:13who displays signs of superior genetic fitness.
05:17This is sexual selection.
05:24And it's driven the skeleton to adapt in some extraordinary ways.
05:34Here I've got another fascinating skull.
05:37Now, this is from an apex predator.
05:39It's from a lion.
05:40These canines are massive, and they're perfectly built to kill.
05:52Lions can attack and kill animals much larger than themselves,
05:57and their teeth are essential for the job.
05:59Look at the size of these canines.
06:05They're almost twice the size of the lions.
06:08But the biggest thing this is likely to hunt is a bug.
06:12And it's far more at home eating fruits from the forest floor.
06:16Now, this is the skull of a mandrill,
06:17the largest species of monkey in the world.
06:20Now, these big canines do have a very important function,
06:24but it has nothing to do with hunting.
06:31Although quite useful when stripping fruit,
06:34they're surplus to requirement.
06:38In mandrill females, canines grow to around a centimetre in length.
06:44But in males, they can reach up to six times longer.
06:48Their teeth have evolved to be this long,
06:54not for eating, but for a different reason.
06:57Reproduction.
07:01In mandrills, big teeth indicate healthy genes.
07:09So for the much smaller females, size does matter.
07:13Because only when a male's canines exceed three centimetres
07:20does he have any chance of being selected for mating.
07:28The mandrill has successfully changed
07:31the primary function of its teeth to aid courtship.
07:38But one vertebrate has gone even further.
07:43This skull glows my mind.
07:48It looks more like an alien,
07:49but there's nothing extraterrestrial about it.
07:52And it is a real animal, I promise,
07:54and it can be found on Earth.
07:56Now, once again, this is a male.
07:59And the most obvious features
08:01are these two things here.
08:04Now, these are modified teeth.
08:05These are the animal's canines.
08:08But unlike mine or the gorillas here,
08:10which grow downwards,
08:12these instead grow up from the skull.
08:16And when they grow, they curve.
08:18And they keep growing and they keep curving.
08:20This can happen to such an extent
08:22that in some very old males,
08:25they've actually been found
08:26to penetrate the bone in the skull.
08:28They go through the brain case
08:29and eventually into the brain.
08:33This would spell certain death for the animal.
08:38Attracting a mate is so important to this species,
08:42they effectively risk their lives in order to do so.
08:49Here you can see just who that skull belongs to.
08:51Now, this is a babirusa,
08:57an animal from the island of Sulawesi in Southeast Asia.
09:03Babirusa are members of the pig family.
09:07Large tusks are only found in males
09:10and appear in adolescence
09:12when they're around a year old.
09:15They start by puncturing the upper lip
09:18and continue to grow throughout the animal's life.
09:23But their specific purpose
09:25has been debated for many years.
09:27Local legends say that babirusa used them
09:34to hang from branches
09:36so they can escape big cats
09:38or spy on females passing below.
09:46Although this story is far-fetched,
09:49females are a factor.
09:52Because for babirusa males,
09:55it's all about getting noticed.
09:58Just like the gorilla's crest
10:00or the mandrel's canines,
10:02researchers believe that tusk length
10:04is a sign of genetic health.
10:07So males with longer, curlier tusks
10:10are more attractive to babirusa females.
10:18Skeletal adaptations play a crucial role in courtship.
10:22But sometimes, the biggest challenge
10:24is actually locating a mate.
10:27And for one elusive species,
10:30brand new research suggests
10:32that the skeleton could help
10:34in tracking down a partner
10:36in the middle of nowhere.
10:38This animal's scientific name,
10:43Monodon monoceros, means one tooth, one horn.
10:48This really is a unique tooth,
10:51and it's the only example in nature
10:53of a tooth that spirals and a tusk that's straight.
10:56This is the narwhal.
11:02Known as the Arctic unicorn,
11:04these strange and secretive members of the whale family
11:07are found in the outer reaches of the northern oceans.
11:11Their remote existence has meant
11:13they're very difficult to study.
11:17Over the centuries,
11:18this has led to many conflicting theories
11:21about the function of their impressive tusk.
11:25Some thought it was an ice-breaking tool.
11:32Others believed it was a weapon
11:34for jousting in the open ocean.
11:36People also thought it was a feeding device,
11:47and this makes sense.
11:48You can imagine the narwhal swimming through the water,
11:51finding a fish, spearing it,
11:54but then it's stuck and it can't get the fish off.
11:57So this idea doesn't work either.
11:59What we now think is that this wonderful tusk
12:01is some sort of sensory organ.
12:03Scientists at Harvard University
12:07believe that males use their sensitive tusks
12:10to find females in this icy wilderness.
12:17The two sexes live apart,
12:19only seeking each other out in the mating season.
12:23The Harvard team believes
12:25that minute sensory pits
12:27along the outside of the tusk are the key.
12:30There are as many as 2,500 in one square millimetre,
12:36and they're thought to sense slight changes
12:38in pressure, temperature, and even salinity.
12:43Early evidence suggests
12:45that by detecting subtle gradient changes
12:47in the water particles,
12:49males can home in on female pods
12:51in the vast open ocean.
12:54Even now, we're just beginning to understand
13:03how important the skeleton is
13:05in the quest to reproduce.
13:07For most vertebrates,
13:14finding a mate is only half the story.
13:20Fighting off rival suitors
13:23is just as important.
13:24As males compete for access to females,
13:39sexual selection has shaped bones
13:41into weapons for combat.
13:46Antlers, horns, and sheer bulk
13:49are all important
13:50when it comes to winning a mate.
13:52But you don't need to be huge
14:07to go into battle.
14:11Hidden in the vaults
14:12of London's Horniman Museum
14:14is a miniature fighter
14:16with some pretty impressive headgear.
14:19This may look like a mini-triceratops,
14:22but it's actually a chameleon.
14:25These three horns are real bone,
14:27and the males use these
14:29for a spot of jousting.
14:34Jackson's chameleons
14:35live in the forests of East Africa,
14:37and even though they're reptiles,
14:39their horns are made of exactly
14:41the same material
14:42as you'd find on a bull.
14:43A bony core
14:48with a keratin sheath
14:50wrapped around it
14:50for strength.
14:53Although tiny,
14:55males can be highly aggressive,
14:57resulting in intense
14:59physical combat.
15:06These featherweight fighters
15:08use their imposing horns
15:09to push each other
15:11out of the treetops
15:12and secure mating rights
15:14with nearby females.
15:25It may seem extreme,
15:28but the stakes are high.
15:31In this battle to reproduce,
15:33there can be only one winner.
15:35But as impressive
15:40as this little guy is,
15:42when it comes to using your head,
15:43there is one animal
15:44that wins hands down.
15:50Bighorn sheep
15:51use their skulls
15:53in a way
15:54that is simply mind-blowing.
15:55In the rocky mountains,
16:03when the mating season arrives,
16:06rams gather
16:07and battle begins.
16:14Usually,
16:15it's the stronger,
16:16older rams
16:17who come out on top.
16:18The prize?
16:20The opportunity to mate.
16:21These brutal tournaments
16:25can last all day
16:27with skulls colliding
16:28at 20 miles an hour.
16:34Their horns can weigh
16:35in excess of 14 kilograms,
16:37more than the rest
16:39of the skeleton combined.
16:42But what's really amazing
16:44is that the key
16:45to this animal's success
16:46is not just
16:47these enormous horns.
16:48The impact force
16:52of the two skulls colliding
16:54can reach almost
16:563,500 newtons.
16:59That's the equivalent
17:00of hitting a baseball
17:02at over 140 kilometers an hour.
17:083,500 newtons
17:10is an impressive force
17:12to take head-on.
17:14And just like a baseball,
17:16the strength
17:17of the bighorn sheep skull
17:19is all in the stitching,
17:21which means
17:22they can take
17:23a lot more impact
17:24than you might think.
17:31Throughout the animal kingdom,
17:33skulls aren't just
17:34one single bone,
17:36but many separate plates
17:38held together by stitches
17:40or sutures.
17:42In most species,
17:44the gap between the plates
17:46becomes fused
17:47once the bone stops growing.
17:50But in bighorns,
17:52things are very different.
17:58Like all skulls,
18:00they're made up
18:00from numerous individual plates,
18:03but the sutures
18:04play a unique role.
18:06At the moment of impact,
18:08the force transmits
18:09through the skull.
18:12The sutures
18:12keep the joins
18:14between each of the plates
18:15flexible,
18:16so they can move freely.
18:19The sutures
18:20act a bit like springs,
18:22absorbing the shock.
18:25The bony sutures
18:27in male bighorns
18:28are also more complex
18:29than in many other vertebrates,
18:31which makes them
18:32immensely strong
18:33and helps prevent
18:34the plates separating
18:36as the skulls collide.
18:46And when you replace
18:47a bighorn skull
18:48with one from
18:49an ordinary sheep,
18:51you can see
18:51exactly what I mean.
18:58To show just how
19:00special bighorn sheep skulls are,
19:03I've devised an experiment
19:04to illustrate
19:05what would happen
19:06to an ordinary sheep skull
19:08without the bighorn's
19:10specialised bony protection.
19:13OK, so I've been
19:14doing the maths
19:14and I've figured out
19:16that if I drop
19:16a 10kg weight
19:17from 3.5m,
19:19when this weight
19:20hits the ground,
19:21that's approximately
19:22the same impact
19:23as two bighorn sheep
19:24smashing heads together.
19:25I've put an old skull
19:31from a regular sheep
19:32on the ground.
19:34Obviously,
19:35things would be
19:35slightly different
19:36if it were still
19:37attached to a living animal,
19:39but it should give
19:40an idea of how
19:41an ordinary sheep skull
19:43measures up
19:43against the forces
19:45exerted on a bighorn.
19:46The sutures
20:00in regular sheep
20:02don't have the same
20:03shock-absorbing capabilities
20:05of a bighorn.
20:05Three and a half
20:15thousand newtons
20:16of force
20:16causes countless
20:18fractures
20:18across the entire skull,
20:22shattering it
20:23into thousands
20:24of tiny fragments.
20:33Whereas in the skull
20:34of a bighorn,
20:35the same impact
20:36is a daily occurrence.
20:46The skeleton
20:48has evolved
20:48to play a crucial role
20:50in maximising
20:51reproductive success.
20:55From courtship
20:56to competing for mates
20:58and even during copulation.
21:00But one bone in particular
21:06has evolved to increase
21:08the chances of fertilisation.
21:14Dr Sam Turvey
21:16from the Zoological Society
21:18of London
21:18is here to show me
21:20which bone that is
21:21and how it functions.
21:23Dr Turvey is an expert
21:27in vertebrate evolution
21:28and is going to kick things off
21:31by testing my knowledge.
21:34What is it then?
21:35Well, I do know what this is.
21:38This is a walrus baculum.
21:41So a penis bone.
21:42That's right.
21:42It is a penis bone.
21:43And I know
21:43it's the largest penis bone
21:45on earth.
21:46I don't know much more than that.
21:47I know we don't have them.
21:48That's right.
21:48But that's about it.
21:49But we're in a minority there.
21:5186% of mammal species
21:53alive today
21:53have got penis bones
21:54of some kind of shape
21:56or size.
21:57There's very different hypotheses
21:58for what they might
21:59or might not do.
22:00Certainly they can
22:00structurally support
22:02and maintain an erection.
22:03And it can definitely allow
22:05longer sex
22:07and more frequent sex.
22:08So, for example,
22:09lions with their bacula
22:10will have sex potentially
22:12up to 100 times a day.
22:13One day?
22:14In one day.
22:15And also,
22:16it will provide
22:16other kinds of structural
22:17integrity as well.
22:18So it will help
22:20keep the urethra open
22:22during sex.
22:22So preventing the tube
22:24through which sperm passes
22:25from kind of being compressed
22:26and collapsed
22:26while sex is happening.
22:28Isn't that really useful?
22:29And also,
22:30they are arguably
22:31the most variable
22:33single bone
22:34shown in any vertebrate.
22:36So there's a vast range
22:37of different sizes
22:38and structures and shapes.
22:39This one's broken as well.
22:40That's incredible
22:41that it's actually survived
22:42and it's healed as well.
22:43We can only hope
22:44that it broke and re-healed
22:45outside the mating season.
22:47I hope.
22:48Is it true that
22:49walrus penises,
22:50walrus penis bones,
22:51were used as clubs?
22:53It is true, yes.
22:55When walrus is being hunted
22:57by people like
22:58the Viking colonists,
22:59the Norse in Greenland
22:59hundreds of years ago,
23:00they'd also harvest
23:02the bacula
23:03from the walrus
23:03at the same time
23:04and whittle them
23:05and carve them
23:05and turn them
23:06into axe handles
23:07and clubs.
23:08So people would have
23:08been killed
23:09by being bashed
23:09on the head
23:10with bacula,
23:10potentially.
23:11Imagine being beaten
23:12to death
23:12with a penis bone.
23:14What's in the bag?
23:15Have a look.
23:15Yes, please.
23:16Well, I've got a test
23:18for you, Mr. Bones.
23:19Can you tell me
23:20which bacula
23:22are from which species?
23:29I can identify one.
23:32This one is mine.
23:33Not mine.
23:34It's mine.
23:35I found this attached
23:37to a very big dead grey seal
23:39up in Scotland last year.
23:41But just having this
23:42next to the walrus
23:43is massively different.
23:44So obviously,
23:44they're a very closely
23:45related species.
23:46They're both pinnipeds.
23:47And obviously,
23:48grey seals are overall
23:49body size
23:50smaller than walruses,
23:51but not by that kind of scale.
23:52This was still
23:52seven and a half foot long,
23:53this animal.
23:54So think about,
23:54walruses are up
23:55in the high arctic
23:56and grey seals
23:58are further down
23:59in temperate regions.
24:00But in warm environments,
24:01you might get animals
24:02congregating together
24:03a bit more,
24:04walrus up in the arctic.
24:05There's very low resources.
24:06Animals are far more
24:07widely dispersed.
24:08And so if a male walrus
24:10encounters a female walrus,
24:11he can't be certain
24:12that female walrus
24:13hasn't already mated
24:13with another male
24:14more recently.
24:15So if you've got
24:16a large baculum,
24:18it can help increase
24:19the chances.
24:20Yeah, basically,
24:21potentially you'd have
24:21more sperm going
24:22into the female,
24:23greater chance
24:24of fertilising the egg.
24:25So typically,
24:26polar species
24:27are more likely
24:28to have large bacula.
24:29So what else have we got?
24:32Well,
24:32I don't know,
24:35they're both
24:35incredibly big,
24:36but...
24:36So these two,
24:37I'm interested
24:37that you picked
24:38those two up
24:38because they're
24:39clearly morphologically
24:40quite similar
24:40to each other
24:41and I'll tell you now,
24:43they are from
24:44very closely related species.
24:45I want to say bear
24:47purely because of the size
24:48and...
24:49Okay.
24:50And bears are
24:51carnivores
24:52which do have bacula,
24:53yeah?
24:53Yeah.
24:53I'm going to say
24:54brown bear
24:55and polar bear.
24:56That's right.
24:57And in fact,
24:58this is from
24:58a Kodiak bear,
24:59which is the largest
25:00subspecies of brown bear,
25:01which is pretty much
25:03the same size
25:03as a polar bear.
25:04But still there's
25:04massive difference
25:05in size and shape
25:06again as well.
25:07So again,
25:07this is probably
25:08a relationship
25:08between polar environment
25:10and more temperate environment
25:12and the relationship
25:13between needing
25:13larger bacula
25:14and polar environments.
25:19I've been buying
25:19myself some time.
25:21Yeah,
25:21I've noticed that.
25:22Tell me which way
25:22round it goes first.
25:23That way.
25:26Attaching,
25:27not attaching,
25:27but...
25:27So this is kind of
25:28like the pelvis
25:29here.
25:29Pelvis end.
25:30Yeah.
25:32I don't know.
25:34Well,
25:34shall I tell you
25:34what it's also called?
25:35Give me a clue.
25:36It's called
25:36a Texas toothpick.
25:38So there's a
25:38geographical clue
25:39what might live in Texas.
25:41There's a carnivore
25:41that lives in Texas
25:42that's got a baculum
25:43that big.
25:44I'm going to go
25:44out on a limb
25:45and say raccoon.
25:47It is a raccoon baculum.
25:49Really?
25:50Full marks,
25:51Mr Bones.
25:51And that's such
25:52a weird shape as well.
25:53It is.
25:54Again,
25:54no one's really
25:55quite sure
25:55exactly why
25:56they're that shape.
25:57The suggestion
25:57is it could be
25:58kind of a lock
25:59and key hypothesis
25:59that could help
26:00it kind of slot
26:01into the female pelvis
26:02a bit better.
26:05So it's interesting,
26:06isn't it?
26:06For a group
26:07of relatively close
26:08related mammals,
26:09they're all
26:09within the carnivora,
26:10the variation in size
26:12and structure
26:12is quite remarkable.
26:14In fact,
26:14bacula are sometimes
26:15used as good
26:16taxonomic indicators
26:17so you can
26:18differentiate species
26:19sometimes solely
26:20on the basis
26:21of the baculum
26:21morphology.
26:22The thing
26:22I like most
26:23is that you
26:24can tell so much
26:25from effectively
26:26one little bone,
26:27whether it's
26:28behaviour
26:28or particular
26:30niches in which
26:31the animal lives
26:31or about the animal
26:32itself.
26:33And for me,
26:34this sums up
26:34perfectly why I love
26:36bones.
26:43Sex has shaped
26:44the vertebrate skeleton
26:45from large and dramatic
26:47adaptations
26:47to the more cryptic
26:50and understated.
26:53This remarkable diversity
26:56has stemmed from one
26:57bony blueprint.
27:00These animals all have
27:03essentially the same
27:05basic skeleton.
27:06skeleton, a skeleton
27:10that has enabled
27:11vertebrates to move,
27:13to sense the world,
27:16to feed,
27:18and to thrive
27:19in every habitat
27:21on earth.
27:25And the extraordinary
27:27secrets of how
27:28each species lives
27:29its life
27:30are hidden
27:32in their bones.
27:35Through looking closely
27:37at their skeletons,
27:38you can tell an animal's
27:39entire life story
27:40from the inside out.
27:42With the incredible
27:44diversity of life
27:45that we have
27:45on our planet,
27:46it's amazing
27:47that one group
27:49of animals
27:49has come to dominate
27:50the land,
27:51the sea,
27:52and the sky.
27:52And this is all
27:54thanks to the
27:56secrets of bones.
27:57and this is all
27:59beautiful things.
27:59Let's get started.
28:00Let's get started.
28:01First of all,
28:01let's get started.
28:02Let's get started.
28:02Let's get started.