0:00:06 > 0:00:08Bones...
0:00:08 > 0:00:11they offer structure, support
0:00:11 > 0:00:13and strength.
0:00:13 > 0:00:17But they have a much bigger story to tell.
0:00:22 > 0:00:26Vertebrates may look very different on the outside,
0:00:26 > 0:00:31but one crucial thing unites them all - the skeleton.
0:00:36 > 0:00:39I'm Ben Garrod, an evolutionary biologist,
0:00:39 > 0:00:42with a very unusual passion.
0:00:42 > 0:00:44This is unbelievable.
0:00:44 > 0:00:47There are too many skeletons for me to look at all at once!
0:00:47 > 0:00:50As a child, I was fascinated by bones.
0:00:52 > 0:00:55Now, skeletons have become my life.
0:00:58 > 0:01:03And I put them together for museums and universities all over the world.
0:01:06 > 0:01:07In this series,
0:01:07 > 0:01:10I've been exploring the natural world...
0:01:10 > 0:01:12from the inside out.
0:01:14 > 0:01:18So far on my journey we've seen how a single, basic body plan
0:01:18 > 0:01:21has given rise to vertebrates of
0:01:21 > 0:01:26practically every possible shape and size.
0:01:26 > 0:01:28Bones have evolved for running...
0:01:29 > 0:01:31..flying...
0:01:31 > 0:01:36hunting...and even sensing the world.
0:01:36 > 0:01:38But there is one significant and defining power
0:01:38 > 0:01:40more important than anything else,
0:01:40 > 0:01:43and bones have a crucial part to play.
0:01:43 > 0:01:47And that is sex.
0:01:47 > 0:01:51'This time, we'll discover just how important the skeleton is
0:01:51 > 0:01:54'in the race to reproduce.
0:01:54 > 0:01:56'From courtship...'
0:01:56 > 0:01:58This skull blows my mind.
0:01:58 > 0:02:02It looks like an alien, but there's nothing extraterrestrial about it.
0:02:02 > 0:02:04'..to competition...'
0:02:04 > 0:02:08When this weight hits the ground, that's approximately the same impact
0:02:08 > 0:02:11as two bighorn sheep smashing their heads together.
0:02:14 > 0:02:16'..and finally copulation.'
0:02:16 > 0:02:19It's the largest penis bone on earth.
0:02:19 > 0:02:22I'm going to reveal the Secrets Of Bones.
0:02:34 > 0:02:37Sex has had a dramatic impact on the vertebrate skeleton.
0:02:42 > 0:02:45And, in the struggle to reproduce,
0:02:45 > 0:02:49animals have evolved some extreme skeletal adaptations
0:02:49 > 0:02:51to maximise their genetic success.
0:02:59 > 0:03:04To begin, I'm going to look at the lengths vertebrates go to
0:03:04 > 0:03:06to stand out in a crowd.
0:03:17 > 0:03:22Attraction isn't always about bright colours, big feathers
0:03:22 > 0:03:24or some impressive dancing.
0:03:26 > 0:03:29It runs bone deep, too.
0:03:30 > 0:03:35And for many vertebrates, the skull is crucial during courtship.
0:03:39 > 0:03:41Take this gorilla skull here, for instance.
0:03:41 > 0:03:44It's got this amazing structure on the back of the skull.
0:03:44 > 0:03:46Now this the sagittal crest.
0:03:46 > 0:03:48And when I see one of these usually it tells me
0:03:48 > 0:03:51that there are massive muscle attachments which go right down
0:03:51 > 0:03:53the side of the face and to the jaw.
0:03:53 > 0:03:56These guys have a very heavy, fibrous diet
0:03:56 > 0:03:59and need to do what we call industrial processing of their food
0:03:59 > 0:04:01where they chew and chew and chew.
0:04:02 > 0:04:06But if this adaptation has evolved purely to help gorillas survive,
0:04:06 > 0:04:10you'd expect to find it in both sexes.
0:04:12 > 0:04:16Although female gorillas have a practically identical diet,
0:04:16 > 0:04:20by comparison, their sagittal crests are much smaller.
0:04:22 > 0:04:24It's only in the big, top males
0:04:24 > 0:04:28you see a crest like this which is just so prominent.
0:04:28 > 0:04:30And I think I know why.
0:04:32 > 0:04:33In adult male gorillas,
0:04:33 > 0:04:38the bony ridge acts as a base for a layer of fatty tissue,
0:04:38 > 0:04:40creating a huge crest.
0:04:43 > 0:04:45But this isn't just for eating,
0:04:45 > 0:04:48it's also for display...
0:04:48 > 0:04:50like a peacock's tail.
0:04:52 > 0:04:57Males with bigger crests tend to attract more mates.
0:05:00 > 0:05:03It's thought that a large ridge is an indicator
0:05:03 > 0:05:06of a strong, healthy individual.
0:05:09 > 0:05:14In the natural world, females are much more likely to select a male
0:05:14 > 0:05:18who displays signs of superior genetic fitness.
0:05:20 > 0:05:23This is sexual selection.
0:05:25 > 0:05:30And it's driven the skeleton to adapt in some extraordinary ways.
0:05:35 > 0:05:37Here I've got another fascinating skull.
0:05:37 > 0:05:41Now this is from an apex predator - it's from a lion.
0:05:41 > 0:05:44These canines are massive
0:05:44 > 0:05:47and they're perfectly built to kill.
0:05:52 > 0:05:57Lions can attack and kill animals much larger than themselves.
0:05:57 > 0:06:00And their teeth are essential for the job.
0:06:03 > 0:06:05Look at the size of these canines -
0:06:05 > 0:06:08they're almost twice the size of the lion's.
0:06:08 > 0:06:13But the biggest thing this is likely to hunt is a bug.
0:06:13 > 0:06:16And it's far more at home eating fruits from the forest floor.
0:06:16 > 0:06:18Now, this is the skull of a mandrill,
0:06:18 > 0:06:21the largest species of monkey in the world.
0:06:21 > 0:06:25Now, these big canines do have a very important function,
0:06:25 > 0:06:27but it has nothing to do with hunting.
0:06:31 > 0:06:34Although quite useful when stripping fruit,
0:06:34 > 0:06:36they're surplus to requirements.
0:06:39 > 0:06:44In mandrill females, canines grow to around a centimetre in length.
0:06:45 > 0:06:49But in males, they can reach up to six times longer.
0:06:52 > 0:06:55Their teeth have evolved to be this long,
0:06:55 > 0:06:58not for eating, but for a different reason - reproduction.
0:07:01 > 0:07:05In mandrills, big teeth indicate healthy genes.
0:07:09 > 0:07:14So, for the much smaller females, size does matter.
0:07:16 > 0:07:20Because only when a male's canines exceed 3cm
0:07:20 > 0:07:24does he have any chance of being selected for mating.
0:07:29 > 0:07:32The mandrill has successfully changed the primary function
0:07:32 > 0:07:34of its teeth to aid courtship.
0:07:39 > 0:07:42But one vertebrate has gone even further.
0:07:45 > 0:07:48This skull blows my mind.
0:07:48 > 0:07:52It looks more like an alien, but there's nothing extraterrestrial
0:07:52 > 0:07:55about it, and it is a real animal, I promise,
0:07:55 > 0:07:57and it can be found on Earth.
0:07:57 > 0:08:00Now, once again, this is a male.
0:08:00 > 0:08:04And the most obvious features are these two things here.
0:08:04 > 0:08:08Now, these are modified teeth. These are the animal's canines,
0:08:08 > 0:08:11but unlike mine or the gorilla's here,
0:08:11 > 0:08:17which grow downwards, these instead grow up from the skull.
0:08:17 > 0:08:19And when they grow, they curve,
0:08:19 > 0:08:21and they keep growing and they keep curving.
0:08:21 > 0:08:25This can happen to such an extent that, in some very old males,
0:08:25 > 0:08:28they've actually been found to penetrate the bone in the skull.
0:08:28 > 0:08:32They go through the brain case and eventually into the brain.
0:08:34 > 0:08:37This would spell certain death for the animal.
0:08:39 > 0:08:42Attracting a mate is so important to the species,
0:08:42 > 0:08:46they effectively risk their lives in order to do so.
0:08:50 > 0:08:52Here you can see just who that skull belongs to.
0:08:56 > 0:08:59Now, this is a babirusa, an animal from the island of Sulawesi
0:08:59 > 0:09:00in Southeast Asia.
0:09:03 > 0:09:06Babirusa are members of the pig family.
0:09:08 > 0:09:11Large tusks are only found in males,
0:09:11 > 0:09:14and appear in adolescence when they are around a year old.
0:09:16 > 0:09:19They start by puncturing the upper lip,
0:09:19 > 0:09:22and continue to grow throughout the animal's life.
0:09:23 > 0:09:28But their specific purpose has been debated for many years.
0:09:32 > 0:09:37Local legends say that babirusa use them to hang from branches,
0:09:37 > 0:09:42so they can escape big cats or spy on females passing below.
0:09:46 > 0:09:51Although this story is far-fetched, females are a factor.
0:09:53 > 0:09:58Because for babirusa males, it's all about getting noticed.
0:09:59 > 0:10:02Just like the gorilla's crest or the mandrill's canines,
0:10:02 > 0:10:06researchers believe that tusk length is a sign of genetic health.
0:10:08 > 0:10:10So males with longer, curlier tusks
0:10:10 > 0:10:13are more attractive to babirusa females.
0:10:18 > 0:10:22Skeletal adaptations play a crucial role in courtship.
0:10:22 > 0:10:27But sometimes the biggest challenge is actually locating a mate.
0:10:28 > 0:10:33And for one elusive species, brand-new research suggests
0:10:33 > 0:10:37that the skeleton could help in tracking down a partner
0:10:37 > 0:10:39in the middle of nowhere.
0:10:41 > 0:10:45This animal's scientific name, Monodon monoceros,
0:10:45 > 0:10:49means one tooth, one horn.
0:10:49 > 0:10:52This really is a unique tooth,
0:10:52 > 0:10:55and it's the only example in nature of a tooth that spirals
0:10:55 > 0:10:57and a tusk that's straight.
0:10:58 > 0:11:00This is the narwhal.
0:11:03 > 0:11:07Known as the Arctic unicorn, these strange and secretive members
0:11:07 > 0:11:09of the whale family are found in the outer reaches
0:11:09 > 0:11:12of the northern oceans.
0:11:12 > 0:11:15Their remote existence has meant they are very difficult to study.
0:11:17 > 0:11:21Over the centuries, this has led to many conflicting theories
0:11:21 > 0:11:24about the function of their impressive tusk.
0:11:26 > 0:11:31Some thought it was an ice breaking tool.
0:11:32 > 0:11:38Others believed it was a weapon for jousting in the open ocean.
0:11:45 > 0:11:48People also thought it was a feeding device, and this makes sense -
0:11:48 > 0:11:51you can imagine the narwhal swimming through the water,
0:11:51 > 0:11:53finding a fish, spearing it.
0:11:55 > 0:11:57But then it's stuck and it can't get the fish off,
0:11:57 > 0:11:59so this idea doesn't work either.
0:11:59 > 0:12:02What we now think is that this wonderful tusk
0:12:02 > 0:12:04is some sort of sensory organ.
0:12:06 > 0:12:08Scientists at Harvard University
0:12:08 > 0:12:13believe that males use their sensitive tusks to find females
0:12:13 > 0:12:14in this icy wilderness.
0:12:17 > 0:12:19The two sexes live apart,
0:12:19 > 0:12:24only seeking each other out in the mating season.
0:12:24 > 0:12:28The Harvard team believes that minute sensory pits
0:12:28 > 0:12:31along the outside of the tusk are the key.
0:12:31 > 0:12:36There are as many as 2,500 in one square millimetre,
0:12:36 > 0:12:40and they're thought to sense slight changes in pressure,
0:12:40 > 0:12:42temperature and even salinity.
0:12:44 > 0:12:48Early evidence suggests that by detecting subtle gradient changes
0:12:48 > 0:12:50in the water particles,
0:12:50 > 0:12:54males can home in on female pods in the vast, open ocean.
0:13:01 > 0:13:04Even now, we're just beginning to understand how important
0:13:04 > 0:13:08the skeleton is in the quest to reproduce.
0:13:13 > 0:13:17For most vertebrates, finding a mate is only half the story.
0:13:22 > 0:13:25Fighting off rival suitors is just as important.
0:13:37 > 0:13:40As males compete for access to females,
0:13:40 > 0:13:44sexual selection has shaped bones into weapons for combat.
0:13:47 > 0:13:51Antlers, horns, and sheer bulk are all important
0:13:51 > 0:13:52when it comes to winning a mate.
0:14:05 > 0:14:09But you don't need to be huge to go into battle.
0:14:11 > 0:14:15Hidden in the vaults of London's Horniman Museum
0:14:15 > 0:14:19is a miniature fighter with some pretty impressive headgear.
0:14:21 > 0:14:23This may look like a mini triceratops,
0:14:23 > 0:14:25but it's actually a chameleon.
0:14:25 > 0:14:28These three horns are real bone,
0:14:28 > 0:14:31and the males use these for a spot of jousting.
0:14:35 > 0:14:38Jackson's chameleons live in the forests of East Africa,
0:14:38 > 0:14:40and, even though they're reptiles,
0:14:40 > 0:14:43their horns are made of exactly the same material
0:14:43 > 0:14:44as you'd find on a bull.
0:14:47 > 0:14:52A bony core with a keratin sheath wrapped around it for strength.
0:14:54 > 0:14:58Although tiny, males can be highly aggressive,
0:14:58 > 0:15:01resulting in intense physical combat.
0:15:07 > 0:15:10These featherweight fighters use their imposing horns
0:15:10 > 0:15:13to push each other out of the tree tops
0:15:13 > 0:15:16and secure mating rights with nearby females.
0:15:26 > 0:15:30It may seem extreme, but the stakes are high.
0:15:32 > 0:15:37In this battle to reproduce, there can be only one winner.
0:15:40 > 0:15:42But, as impressive as this little guy is,
0:15:42 > 0:15:44when it comes to using your head,
0:15:44 > 0:15:46there is one animal that wins hands down.
0:15:51 > 0:15:59Bighorn sheep use their skulls in a way that is simply mind-blowing.
0:16:02 > 0:16:04In the Rocky Mountains,
0:16:04 > 0:16:07when the mating season arrives, rams gather...
0:16:09 > 0:16:11..and battle begins.
0:16:15 > 0:16:19Usually, it's the stronger, older rams who come out on top.
0:16:19 > 0:16:21The prize is the opportunity to mate.
0:16:24 > 0:16:27These brutal tournaments can last all day
0:16:27 > 0:16:32with skulls colliding at 20mph.
0:16:34 > 0:16:38Their horns can weigh in excess of 14kg -
0:16:38 > 0:16:40more than the rest of the skeleton combined.
0:16:43 > 0:16:47But what's really amazing is that the key to this animal's success
0:16:47 > 0:16:49is not just these enormous horns.
0:16:52 > 0:16:55The impact force of the two skulls colliding
0:16:55 > 0:16:58can reach almost 3,500 newtons.
0:17:00 > 0:17:03That's the equivalent of hitting a baseball
0:17:03 > 0:17:06at over 140 kilometres an hour.
0:17:09 > 0:17:153,500 newtons is an impressive force to take head-on.
0:17:15 > 0:17:17And, just like a baseball,
0:17:17 > 0:17:22the strength of the bighorn sheep skull is all in the stitching.
0:17:22 > 0:17:27Which means they can take a lot more impact than you might think.
0:17:32 > 0:17:37Throughout the animal kingdom, skulls aren't just one single bone,
0:17:37 > 0:17:43but many separate plates held together by stitches or sutures.
0:17:43 > 0:17:47In most species, the gap between the plates
0:17:47 > 0:17:49becomes fused once the bone stops growing.
0:17:51 > 0:17:54But in bighorns, things are very different.
0:17:59 > 0:18:03Like all skulls, they're made up from numerous individual plates,
0:18:03 > 0:18:07but the sutures play a unique role.
0:18:07 > 0:18:12At the moment of impact, the force transmits through the skull.
0:18:12 > 0:18:17The sutures keep the joins between each of the plates flexible
0:18:17 > 0:18:19so they can move freely.
0:18:19 > 0:18:23The sutures act a bit like springs, absorbing the shock.
0:18:26 > 0:18:30The bony sutures in male bighorns are also more complex
0:18:30 > 0:18:34than in many other vertebrates, which makes them immensely strong
0:18:34 > 0:18:38and helps prevent the plates separating as the skulls collide.
0:18:47 > 0:18:51And when you replace a bighorn skull with one from an ordinary sheep,
0:18:51 > 0:18:53you can see exactly what I mean.
0:18:58 > 0:19:03To show just how special bighorn sheep skulls are,
0:19:03 > 0:19:07I've devised an experiment to illustrate what would happen
0:19:07 > 0:19:09to an ordinary sheep skull
0:19:09 > 0:19:13without the bighorn's specialised bony protection.
0:19:13 > 0:19:15OK, so I've been doing the maths
0:19:15 > 0:19:18and I've figured out that if I drop a 10kg weight
0:19:18 > 0:19:20from three-and-a-half metres,
0:19:20 > 0:19:23when this weight hits the ground, that's approximately the same impact
0:19:23 > 0:19:26as two bighorn sheep smashing their heads together.
0:19:30 > 0:19:34I've put an old skull from a regular sheep on the ground.
0:19:34 > 0:19:37Obviously, things would be slightly different
0:19:37 > 0:19:40if it were still attached to a living animal.
0:19:40 > 0:19:43But it should give an idea of how an ordinary sheep skull
0:19:43 > 0:19:47measures up against the forces exerted on a bighorn.
0:20:00 > 0:20:02The sutures in regular sheep
0:20:02 > 0:20:06don't have the same shock-absorbing capabilities of a bighorn.
0:20:14 > 0:20:193,500 newtons of force causes countless fractures
0:20:19 > 0:20:21across the entire skull.
0:20:23 > 0:20:26Shattering it into thousands of tiny fragments.
0:20:34 > 0:20:36Whereas in the skull of a bighorn,
0:20:36 > 0:20:39the same impact is a daily occurrence.
0:20:47 > 0:20:51The skeleton has evolved to play a crucial role
0:20:51 > 0:20:53in maximising reproductive success.
0:20:56 > 0:20:59From courtship, to competing for mates
0:20:59 > 0:21:01and even during copulation.
0:21:05 > 0:21:09But one bone in particular has evolved to increase
0:21:09 > 0:21:10the chances of fertilisation.
0:21:15 > 0:21:19Dr Sam Turvey from the Zoological Society of London
0:21:19 > 0:21:24is here to show me which bone that is and how it functions.
0:21:26 > 0:21:29Dr Turvey is an expert in vertebrate evolution
0:21:29 > 0:21:34and is going to kick things off by testing my knowledge.
0:21:34 > 0:21:36What is it, then?
0:21:36 > 0:21:39Well, I do know what this is.
0:21:39 > 0:21:41This is a walrus baculum.
0:21:41 > 0:21:43- So, a penis bone. - That's right, it is a penis bone.
0:21:43 > 0:21:46And I know it's the largest penis bone on Earth.
0:21:46 > 0:21:48I don't know much more than that. I know we don't have them...
0:21:48 > 0:21:50- That's right.- ..but that's about it.
0:21:50 > 0:21:54But we're in a minority there - 86% of mammal species alive today
0:21:54 > 0:21:57have got penis bones of some kind of shape or size.
0:21:57 > 0:22:00There's various different hypotheses for what they might or might not do.
0:22:00 > 0:22:04Certainly, they can structurally support and maintain an erection,
0:22:04 > 0:22:08and it can definitely allow longer sex and more frequent sex.
0:22:08 > 0:22:12So, for example, lions with their bacula will have sex
0:22:12 > 0:22:15- potentially up to 100 times a day. - One day?- In one day.
0:22:15 > 0:22:18And, also, it will provide other kinds of structural integrity,
0:22:18 > 0:22:23as well. So it will help keep the urethra open during sex,
0:22:23 > 0:22:25so preventing the tube through which sperm passes
0:22:25 > 0:22:28from being kind of being compressed and collapsed while sex is happening.
0:22:28 > 0:22:30So they're really useful.
0:22:30 > 0:22:35And also they are arguably the most variable single bone
0:22:35 > 0:22:36shown in any vertebrate.
0:22:36 > 0:22:39So there's a vast range of different sizes and structures and shapes.
0:22:39 > 0:22:42This one's broken, as well. That's incredible -
0:22:42 > 0:22:44that it's actually survived and it's healed, as well.
0:22:44 > 0:22:48We can only hope that it broke and re-healed outside the mating season!
0:22:48 > 0:22:52I hope! Is it true that walrus penises, walrus penis bones,
0:22:52 > 0:22:55- were used as clubs?- It is true, yes.
0:22:55 > 0:22:59When walruses were being hunted by people like the Viking colonists,
0:22:59 > 0:23:01the Norse in Greenland hundreds of years ago,
0:23:01 > 0:23:04they'd also harvest the bacula from the walruses at the same time
0:23:04 > 0:23:08and whittle them and carve them and turn them into axe handles and clubs.
0:23:08 > 0:23:10So people would have been killed by being bashed on the head
0:23:10 > 0:23:12with bacula, potentially.
0:23:12 > 0:23:14Imagine being beaten to death with a penis bone.
0:23:14 > 0:23:17- What's in the bag? - Let's have a look.
0:23:17 > 0:23:19Well, I've got a test for you, Mr Bones.
0:23:19 > 0:23:25Can you tell me which bacula are from which species?
0:23:29 > 0:23:31I can identify one.
0:23:33 > 0:23:35This one is mine. Not mine!
0:23:35 > 0:23:38- It is mine.- It is yours. - I found this attached
0:23:38 > 0:23:41to a very big, dead grey seal up in Scotland last year.
0:23:41 > 0:23:45But just having this next to the walrus, it's massively different.
0:23:45 > 0:23:49There are very closely-related species. They're both pinnipeds, and obviously grey seals are,
0:23:49 > 0:23:51overall body size wise, smaller than walruses.
0:23:51 > 0:23:55- But not by that kind of scale. - This was still seven-and-a-half foot long, this animal.
0:23:55 > 0:23:57Walruses are up in the High Arctic,
0:23:57 > 0:24:00and grey seals are further down in temperate regions.
0:24:00 > 0:24:04But in warmer environments, you might get animals congregating together
0:24:04 > 0:24:07a bit more. Whereas up in the Arctic, there's very low resources.
0:24:07 > 0:24:10Animals are far more widely dispersed and so if a male walrus
0:24:10 > 0:24:13encounters a female walrus, he can't be certain that female walrus
0:24:13 > 0:24:16hasn't already mated with another male more recently.
0:24:16 > 0:24:20- So if you've got a large baculum, it can help...- Increase your chances.
0:24:20 > 0:24:23Yeah, basically, potentially, you'd have more sperm going
0:24:23 > 0:24:26into the female, a lot greater chance of fertilising the egg.
0:24:26 > 0:24:30So, typically, polar species are more likely to have larger bacula.
0:24:30 > 0:24:32So what else we got?
0:24:32 > 0:24:34Well...
0:24:34 > 0:24:37I don't know, they're both incredibly big, but...
0:24:37 > 0:24:39So these two... It's interesting that you picked those two up,
0:24:39 > 0:24:42because they're clearly morphologically quite similar
0:24:42 > 0:24:44to each other, and, I'll tell you now,
0:24:44 > 0:24:46they are from very closely-related species.
0:24:46 > 0:24:49I want to say bear purely because of the size and...
0:24:49 > 0:24:53OK. And bears are carnivores which do have bacula.
0:24:53 > 0:24:57I'm going to say brown bear and polar bear.
0:24:57 > 0:24:59That's right. In fact, this is from a Kodiak bear,
0:24:59 > 0:25:02which is the largest subspecies of brown bear,
0:25:02 > 0:25:04which is pretty much the same size as a polar bear.
0:25:04 > 0:25:07But still, there's a massive difference in size and shape.
0:25:07 > 0:25:09So, again, this is probably the relationship
0:25:09 > 0:25:13between polar environment and more temperate environment,
0:25:13 > 0:25:16and the relationship between needing larger bacula in polar environments.
0:25:19 > 0:25:23- I've been buying myself some time. - Yeah, I've noticed that.
0:25:23 > 0:25:26Tell me which way round it goes first.
0:25:26 > 0:25:30- That way, attaching...- So this is kind of like the pelvis here.
0:25:32 > 0:25:35- I don't know.- Well, shall I tell you what it's also called?
0:25:35 > 0:25:38- Give me a clue. - It's called a Texas Toothpick.
0:25:38 > 0:25:41So it's a geographical clue. What might live in Texas?
0:25:41 > 0:25:43It's a carnivore that lives in Texas,
0:25:43 > 0:25:45that's got a baculum that big.
0:25:45 > 0:25:48I'm going to go out on a limb and say raccoon.
0:25:48 > 0:25:50- It is a raccoon baculum. - Really?
0:25:50 > 0:25:53- Full marks, Mr Bones. - That's such a weird shape, as well.
0:25:53 > 0:25:57It is. Again, no-one's really quite sure exactly why they're that shape.
0:25:57 > 0:26:00The suggestion is that it can be a kind of lock-and-key hypothesis.
0:26:00 > 0:26:04That could help it kind of slot into the female pelvis a bit better.
0:26:05 > 0:26:07So, it's interesting, isn't it?
0:26:07 > 0:26:09For a group of relatively closely related mammals,
0:26:09 > 0:26:11they're all within the Carnivora,
0:26:11 > 0:26:14the variation in size and structure is quite remarkable.
0:26:14 > 0:26:18In fact, bacula are sometimes used as good taxonomic indicators -
0:26:18 > 0:26:20ie you can differentiate species,
0:26:20 > 0:26:22sometimes solely on the basis of their baculum morphology.
0:26:22 > 0:26:25The thing that I like most is that you can tell so much from,
0:26:25 > 0:26:29effectively, one little bone - whether it's behaviour,
0:26:29 > 0:26:32or particular niches in which the animal lives
0:26:32 > 0:26:34or about the animal itself.
0:26:34 > 0:26:37And, for me, this sums up perfectly why I love bones.
0:26:43 > 0:26:46Sex has shaped the vertebrate skeleton -
0:26:46 > 0:26:52from large and dramatic adaptations to the more cryptic and understated.
0:26:54 > 0:26:59This remarkable diversity has stemmed from one bony blueprint.
0:27:01 > 0:27:07These animals all have essentially the same basic skeleton.
0:27:09 > 0:27:12A skeleton that has enabled vertebrates to move...
0:27:14 > 0:27:16..to sense the world,
0:27:16 > 0:27:22to feed, and to thrive in every habitat on Earth.
0:27:26 > 0:27:31And the extraordinary secrets of how each species lives its life
0:27:31 > 0:27:34are hidden in their bones.
0:27:36 > 0:27:39Through looking closely at their skeletons,
0:27:39 > 0:27:43you can see an animal's entire life story from the inside out.
0:27:43 > 0:27:47With the incredible diversity of life that we have on our planet,
0:27:47 > 0:27:51it's amazing that one group of animals has come to dominate
0:27:51 > 0:27:54the land, the sea and the sky.
0:27:54 > 0:27:58And this is all thanks to the secrets of bones.