0:00:18 > 0:00:22More than eight million animal species live on the planet today.
0:00:26 > 0:00:30Only a special few are armed with extreme weapons.
0:00:36 > 0:00:39Huge physical appendages growing from their bodies.
0:00:41 > 0:00:45Look at that set of antlers, wow!
0:00:45 > 0:00:47Wielded in titanic battles.
0:00:54 > 0:00:58What gives rise to these enormous structures?
0:00:58 > 0:01:00When the conditions are just right,
0:01:00 > 0:01:03these weapons can get caught up in arms races.
0:01:03 > 0:01:06Are they more than just instruments of blunt force?
0:01:08 > 0:01:11Can you show me the biggest weapon in the animal world?
0:01:11 > 0:01:12Absolutely.
0:01:12 > 0:01:15And what can their evolution teach us about our own arms race?
0:01:18 > 0:01:21Three, two, one, turn.
0:01:41 > 0:01:43In south-west Montana is a bizarre armoury...
0:01:46 > 0:01:49..created from a collection of naturally-shed antlers.
0:01:59 > 0:02:00Oh, my God!
0:02:01 > 0:02:03Wow!
0:02:05 > 0:02:06Unbelievable.
0:02:09 > 0:02:12Doug Emlen is a professor of biology.
0:02:12 > 0:02:15He spent his lifetime trying to unlock the secrets
0:02:15 > 0:02:17of extreme animal weapons.
0:02:20 > 0:02:21Look at this!
0:02:22 > 0:02:26This is an antler from an elk, a bull elk from here in Montana.
0:02:26 > 0:02:28This is 20lbs of bone.
0:02:28 > 0:02:31And they, of course, produce two of them every year.
0:02:31 > 0:02:33Antlers are the fastest-growing bones
0:02:33 > 0:02:35described from any living vertebrae.
0:02:39 > 0:02:41Nature's armoury is diverse...
0:02:43 > 0:02:45..horns...
0:02:48 > 0:02:49..tusks...
0:02:51 > 0:02:52..stings.
0:02:53 > 0:02:54They can be used for attack...
0:02:58 > 0:02:59..or for protection.
0:03:03 > 0:03:07Almost any animal has a weapon, of one sort or another.
0:03:07 > 0:03:10I mean, cats have claws, eagles have talons,
0:03:10 > 0:03:13even dogs have a respectable set of teeth.
0:03:14 > 0:03:17But those weapons stay small. There's nothing big or awkward
0:03:17 > 0:03:19or anything that would slow these animals down.
0:03:19 > 0:03:23Nothing sticking out of their bodies, in some crazy way.
0:03:24 > 0:03:27But here and there, sprinkled through the tree of life,
0:03:27 > 0:03:31are species where their weapons are taken to an extreme.
0:03:33 > 0:03:35For me, I'm interested in the weapons of offence,
0:03:35 > 0:03:39weapons that are used in fighting and, in particular,
0:03:39 > 0:03:41the weapons that are big.
0:03:41 > 0:03:43Those are the species that keep me awake at night.
0:03:55 > 0:03:58Luckily for Doug, he can find perfect subjects
0:03:58 > 0:04:00right on his doorstep in Montana.
0:04:07 > 0:04:08Look at that guy.
0:04:09 > 0:04:10Look at him.
0:04:12 > 0:04:14Rancher Doug Averill keeps elk on his land.
0:04:17 > 0:04:20Amongst them are a number of mature males.
0:04:23 > 0:04:24During the autumn rut,
0:04:24 > 0:04:28the antlers of these bull elk are at their most impressive.
0:04:28 > 0:04:30ELK BELLOWS
0:04:32 > 0:04:33Here comes another one.
0:04:37 > 0:04:39They're all going to size each other up here,
0:04:39 > 0:04:41when you get this many bulls together.
0:04:42 > 0:04:44This might get interesting.
0:04:45 > 0:04:47Fuelled by testosterone,
0:04:47 > 0:04:50the biggest bulls are looking to assert their dominance.
0:04:52 > 0:04:55When it's not in the rutting season, they're relatively calm,
0:04:55 > 0:04:59peaceful animals. But it's kind of like a bunch of guys on Friday night
0:04:59 > 0:05:01at the bar!
0:05:14 > 0:05:18This is pretty rare. I haven't seen this all summer.
0:05:24 > 0:05:27And you can see, they're totally locked together.
0:05:39 > 0:05:42The larger bull on the right has won this round...
0:05:46 > 0:05:48..but the loser still wants a fight.
0:05:49 > 0:05:52He has the temperament to be an aggressive bull down the road.
0:06:00 > 0:06:01It got my attention!
0:06:03 > 0:06:04It's OK.
0:06:07 > 0:06:11Despite being charged, Doug can't resist getting closer.
0:06:17 > 0:06:20I love living in Montana and this is why.
0:06:21 > 0:06:23Got two bull elks sparring behind me.
0:06:25 > 0:06:27After shedding last year's rack,
0:06:27 > 0:06:30the bulls have spent just six months growing this season's antlers.
0:06:32 > 0:06:34Imagine the amount of resources that it takes
0:06:34 > 0:06:37to produce something like this.
0:06:37 > 0:06:40That would be like me producing another leg and wearing it around
0:06:40 > 0:06:42on my head. They'll shed this,
0:06:42 > 0:06:45they'll throw this away at the end of the season and then they have to
0:06:45 > 0:06:48turn right around and start growing a whole other one again.
0:06:48 > 0:06:52The only way they can grow a bone this big, this fast,
0:06:52 > 0:06:55is to shunt the calcium, shunt the minerals,
0:06:55 > 0:06:57away from the rest of the bones in their body.
0:06:57 > 0:07:00So they're literally pulling these things out of the rest of their
0:07:00 > 0:07:03skeleton and allocating it to the weapons.
0:07:03 > 0:07:08They actually go through a seasonal period of osteoporosis.
0:07:08 > 0:07:12The biggest bulls and bucks have brittle bones at exactly the time
0:07:12 > 0:07:15of year when they're hurling themselves against each other
0:07:15 > 0:07:16in all-out battles.
0:07:17 > 0:07:21An antler can grow an extraordinary four centimetres a day.
0:07:21 > 0:07:23The amount of energy required is huge.
0:07:24 > 0:07:26Often by the end of the rut,
0:07:26 > 0:07:29bulls will have lost as much as a quarter of their body weight.
0:07:29 > 0:07:33They come out of that season starved and scratched
0:07:33 > 0:07:34and scarred and damaged,
0:07:34 > 0:07:37and they've only got a few short weeks to make up the calories
0:07:37 > 0:07:40they've lost before winter or they're not going to survive.
0:07:42 > 0:07:44Elk need to stay strong.
0:07:45 > 0:07:47ELK BELLOWS
0:07:47 > 0:07:50The weakest are the most likely to become prey.
0:07:51 > 0:07:54So, imagine the predators of these guys, something like a wolf.
0:07:56 > 0:07:59Wolves have to be fast, they have to be agile.
0:07:59 > 0:08:00Think about what would happen to
0:08:00 > 0:08:03a wolf if it had a set of antlers on the top of its head.
0:08:03 > 0:08:06A wolf that awkward wouldn't be fast enough to catch
0:08:06 > 0:08:08their prey. They wouldn't be able to turn quickly enough
0:08:08 > 0:08:10to catch their prey.
0:08:12 > 0:08:15But now if you turn around and you look at the elk, well,
0:08:15 > 0:08:18it doesn't make sense there, either.
0:08:18 > 0:08:20I mean, elk have to be able to escape,
0:08:20 > 0:08:23they have to be able to be agile and to run fast
0:08:23 > 0:08:25and antlers are going to slow them down just as much
0:08:25 > 0:08:26as it slows down a wolf.
0:08:28 > 0:08:31You might think that the primary function of an antler is to protect
0:08:31 > 0:08:32that elk from a wolf.
0:08:32 > 0:08:35But it's not. Even though a bull might be able to do some damage
0:08:35 > 0:08:37with its tines...
0:08:37 > 0:08:38WOLF WHIMPERS
0:08:38 > 0:08:41..it's not going to be enough to save it from predation.
0:08:47 > 0:08:50Considering what we know about the costs of these weapons,
0:08:50 > 0:08:52why would you ever want one?
0:08:52 > 0:08:55These structures are not helping the bull survive.
0:08:58 > 0:09:01So what's the point of these extreme weapons?
0:09:04 > 0:09:06Survivorship isn't the only game in town.
0:09:06 > 0:09:08And, in fact, when it comes to evolution,
0:09:08 > 0:09:11the thing that matters the most is reproduction.
0:09:15 > 0:09:18Animals have evolved a multitude of weird and wonderful traits to help
0:09:18 > 0:09:20them seduce a mate.
0:09:25 > 0:09:26Tails...
0:09:29 > 0:09:30..noses...
0:09:31 > 0:09:32..even bottoms.
0:09:36 > 0:09:39All can be used to attract the opposite sex.
0:09:42 > 0:09:45This improves the chance that they will pass their genes on to
0:09:45 > 0:09:46the next generation.
0:09:48 > 0:09:53So, how do extreme weapons increase an animal's ability to reproduce?
0:09:58 > 0:10:01For elk, antlers are worth the cost.
0:10:01 > 0:10:06The biggest bulls with the largest antlers tend to win the most fights.
0:10:08 > 0:10:12The winners mate with more females and produce the most offspring.
0:10:15 > 0:10:17For animals that bear arms,
0:10:17 > 0:10:23this is the evolutionary advantage extreme weapons provide.
0:10:23 > 0:10:25ELK CALLS
0:10:28 > 0:10:33But arms races only occur in a relatively small number of species.
0:10:33 > 0:10:35So what are the conditions that spark them?
0:10:36 > 0:10:39Finding the answer isn't straightforward.
0:10:39 > 0:10:42Particularly when many of your subjects can't be studied in a lab.
0:10:44 > 0:10:46For the kinds of things that we want to study,
0:10:46 > 0:10:50it's a little difficult to raise elk in captivity.
0:10:50 > 0:10:53We work on a much smaller critter.
0:10:53 > 0:10:54We work on beetles.
0:10:56 > 0:10:58In this particular species,
0:10:58 > 0:11:01the males have a horn that's like a pitchfork that sticks forward
0:11:01 > 0:11:02from the front of their heads.
0:11:02 > 0:11:05And in some of the specimens, these pitchforks can be almost as long
0:11:05 > 0:11:06as the whole rest of the body.
0:11:07 > 0:11:10This might look small relative to an elk,
0:11:10 > 0:11:13but I assure you, as far as insects are concerned, this is big.
0:11:13 > 0:11:15Every bit as impressive.
0:11:15 > 0:11:17It can be 30% of their body weight.
0:11:17 > 0:11:21That is, literally, like you or me wearing a coffee table around on
0:11:21 > 0:11:24the tops of our heads. So, imagine doing everything you do,
0:11:24 > 0:11:28from waking up in the morning, to everything you do during a day,
0:11:28 > 0:11:30with a coffee table fused to the top of your head.
0:11:30 > 0:11:32And now you've got a little taste of what it's like to be one
0:11:32 > 0:11:34of these beetles.
0:11:50 > 0:11:53Doug's fascination with biology began as a young boy.
0:11:56 > 0:12:00He travelled the world investigating all types of animal arms races.
0:12:03 > 0:12:07Slowly, he's been piecing together evidence to explain the evolution
0:12:07 > 0:12:08of extreme weapons.
0:12:12 > 0:12:15So, there's an animal with an incredible weapon.
0:12:15 > 0:12:18They're a different lineage of beetles from the ones that we study.
0:12:18 > 0:12:22These guys live in Chile, but their story's exactly the same.
0:12:22 > 0:12:26That is one of the biggest weapons of any living animal - ever.
0:12:29 > 0:12:32They've got mouthparts or mandibles that have been elongated, so that
0:12:32 > 0:12:35they have these curved, arcing pincers.
0:12:35 > 0:12:38The males grow up to nine centimetres long.
0:12:39 > 0:12:42Their specially-adapted jaws can be half their body length.
0:12:45 > 0:12:47So, the males are fighting battles with rival males.
0:12:47 > 0:12:50So, these are two males sparring and facing off against each other,
0:12:50 > 0:12:52trying to fling each other from the tree.
0:13:13 > 0:13:14For the loser, it's a long way down.
0:13:19 > 0:13:22The battles between beetles offer the first clue to the special
0:13:22 > 0:13:25circumstances that trigger animal arms races.
0:13:28 > 0:13:30Beetles like this fight over wounds,
0:13:30 > 0:13:34sort of marks or nicks on the side of a tree, where sap will ooze out
0:13:34 > 0:13:35and drip down the side.
0:13:38 > 0:13:40The sap attracts females, like this one.
0:13:41 > 0:13:44Unlike the males, she has small jaws.
0:13:45 > 0:13:48If you're a male and you can hold on to that real estate,
0:13:48 > 0:13:50you have opportunities to mate with
0:13:50 > 0:13:51the females when they come in to feed.
0:13:53 > 0:13:57It's not an accident that castles are located on the tops of hills
0:13:57 > 0:14:00or out on the ends of long moats and surrounded by water.
0:14:00 > 0:14:04We've known for centuries that things that are physically isolated,
0:14:04 > 0:14:08or that have restricted access, are much more economical to defend.
0:14:08 > 0:14:11Exactly the same logic applies to animals.
0:14:11 > 0:14:14The males that are able to win these battles or to hold on to that
0:14:14 > 0:14:17territory, I mean, the ultimate prize is reproduction.
0:14:22 > 0:14:24This male has fought off all his rivals.
0:14:25 > 0:14:28And now he's earned the opportunity to mate with a female.
0:14:32 > 0:14:34So when we start to look at these animals and say,
0:14:34 > 0:14:36"What sets these species apart?
0:14:36 > 0:14:40"Why do these particular species have such incredible weapons?"
0:14:40 > 0:14:43The first clue, the first piece of the puzzle,
0:14:43 > 0:14:47is a defendable resource against which the fights can take place.
0:14:49 > 0:14:52So imagine things that whirl around in the water.
0:14:54 > 0:14:57Sometimes animals are fighting over resources that can't be defended.
0:15:02 > 0:15:05Think about things like raptors fighting in the air.
0:15:08 > 0:15:10EAGLES SQUAWK
0:15:10 > 0:15:14They'll get into these big, frenzied, acrobatic mid-air snarls.
0:15:18 > 0:15:20And fights like that,
0:15:20 > 0:15:23things like agility or speed are likely to matter more than
0:15:23 > 0:15:25bulk and strength.
0:15:28 > 0:15:32For these kinds of fights, big weapons just aren't worth the price.
0:15:42 > 0:15:45A defendable resource is one of the critical requirements for an animal
0:15:45 > 0:15:46arms race to begin.
0:15:50 > 0:15:53And often, females are the resource.
0:15:59 > 0:16:03Male hippos use their enormous teeth in fights to guard harems of females
0:16:03 > 0:16:04from adversaries.
0:16:09 > 0:16:13Male white rhinos use their horns to protect territories that females
0:16:13 > 0:16:14travel through.
0:16:17 > 0:16:21And male elephants use their tusks in combat to defend fertile females
0:16:21 > 0:16:22from rivals.
0:16:26 > 0:16:27I love elephants!
0:16:35 > 0:16:38Each of those tusks can be, like, 100lbs of ivory.
0:16:38 > 0:16:40These are huge teeth.
0:16:42 > 0:16:45Bull elephant tusks are the biggest and heaviest teeth in nature.
0:17:01 > 0:17:04Oh, his tusk's shattered.
0:17:04 > 0:17:06OK, there you go, that's the impact that we're talking about here.
0:17:19 > 0:17:20These are fantastic weapons,
0:17:20 > 0:17:22partly because they're lethal in their own right,
0:17:22 > 0:17:25they're able to stab, but they also allow these guys to,
0:17:25 > 0:17:27like, push and strain against each other and size each other up.
0:17:29 > 0:17:32There's a deeper story behind the bull's tusks.
0:17:32 > 0:17:37One that's vital for all animal arms races.
0:17:37 > 0:17:39Bull elephants have these massive tusks.
0:17:39 > 0:17:41But if we want to understand the tusks,
0:17:41 > 0:17:43we actually have to look at the females.
0:17:44 > 0:17:47Female elephants also have tusks.
0:17:47 > 0:17:51Theirs are smaller and not used for fighting in the same way as males.
0:17:54 > 0:17:58But it's the details of the female's reproductive cycle that explains
0:17:58 > 0:18:00the evolution of the male's bigger tusks.
0:18:02 > 0:18:06Female elephants are pregnant for 22 months and, after they give birth,
0:18:06 > 0:18:08they take care of their young for another two years.
0:18:12 > 0:18:16A female will only be fertile for five days out of every four years.
0:18:16 > 0:18:19That's an incredibly brief window of time.
0:18:19 > 0:18:22It's less than one half of 1% of a female's lifetime.
0:18:24 > 0:18:27So, that means, when you look across the landscape and you look at the
0:18:27 > 0:18:29male and female elephants out there,
0:18:29 > 0:18:33you're going to find that pretty much all of the bulls are ready
0:18:33 > 0:18:35to breed at any point in time.
0:18:35 > 0:18:39Every now and then, a female will become receptive and when she goes
0:18:39 > 0:18:40into that window of fertility,
0:18:40 > 0:18:43every male on the landscape enters into the fray.
0:18:45 > 0:18:47Male elephants will travel for hundreds of miles
0:18:47 > 0:18:49to find a fertile female.
0:18:52 > 0:18:55Whenever there are more individuals of one sex able to breed than
0:18:55 > 0:18:57the other, the result is going to be competition.
0:19:00 > 0:19:03If you think of nearly any reproducing species,
0:19:03 > 0:19:06you'll find that the females are invariably unable to breed
0:19:06 > 0:19:08for long periods of time.
0:19:11 > 0:19:13Female mammals become pregnant...
0:19:15 > 0:19:16..they provide milk and care
0:19:16 > 0:19:18for their offspring until independence...
0:19:20 > 0:19:22..before reproducing again.
0:19:25 > 0:19:27After laying their eggs,
0:19:27 > 0:19:30female birds usually incubate and raise their chicks before they can
0:19:30 > 0:19:32breed once more.
0:19:36 > 0:19:38The same trend is repeated in many animals.
0:19:44 > 0:19:45PUP WHIMPERS
0:19:49 > 0:19:52Males are almost always ready to breed.
0:19:54 > 0:19:58But reproductive females are rare and this sets the stage
0:19:58 > 0:20:00for intense male rivalry.
0:20:03 > 0:20:04In all of these animals where you
0:20:04 > 0:20:07get these massive weapons, the males -
0:20:07 > 0:20:10the bulls, the bucks - they face fierce competition.
0:20:10 > 0:20:13And we think now that it's that second
0:20:13 > 0:20:15critical ingredient for an arms race.
0:20:26 > 0:20:29Competition is the second condition needed for animals
0:20:29 > 0:20:31to evolve extreme weapons.
0:20:38 > 0:20:40But must it always be the males?
0:20:41 > 0:20:45Can competition ever cause females to evolve big weapons and fight?
0:20:52 > 0:20:5630 years ago, behavioural ecologist Stephen Emlen discovered a key piece
0:20:56 > 0:20:58of evidence to help answer this.
0:21:00 > 0:21:03I haven't seen this in a long time!
0:21:05 > 0:21:08He helped capture some remarkable film of an unusual tropical bird...
0:21:10 > 0:21:11..the Jacana.
0:21:11 > 0:21:15Sometimes these are called Jesus Christ birds because they
0:21:15 > 0:21:17seemingly walk on water because their toes are so long,
0:21:17 > 0:21:19they spread out their weight.
0:21:21 > 0:21:25Male Jacanas are small. They incubate eggs in a nest
0:21:25 > 0:21:26and raise the chicks.
0:21:28 > 0:21:30Most females are bigger.
0:21:30 > 0:21:33She'll defend large territories where many males may live.
0:21:34 > 0:21:38Her only parental duty is to lay eggs in the male's nest.
0:21:40 > 0:21:44So time-wise, the female, she is able to reproduce, in theory,
0:21:44 > 0:21:46about every ten days. She could lay another clutch.
0:21:46 > 0:21:50He's stuck for almost three months tending the eggs and the chicks.
0:21:51 > 0:21:53So the tables are turned and that
0:21:53 > 0:21:56means that females have to compete with each other
0:21:56 > 0:21:59- for access to the males. - Absolutely. Smart son!
0:21:59 > 0:22:00HE LAUGHS
0:22:01 > 0:22:03Stephen is Doug's father.
0:22:04 > 0:22:07He pioneered studies, to show the effect of competition
0:22:07 > 0:22:08on weapon development.
0:22:10 > 0:22:14So, not only are the males doing the parental care,
0:22:14 > 0:22:17but it means the females are fighting over access to the males.
0:22:17 > 0:22:19And so the expectation is they
0:22:19 > 0:22:21should have larger weapons than males.
0:22:23 > 0:22:26These Jacanas have a single sharp yellow spur on each wing.
0:22:28 > 0:22:30They're made of a tough, fingernail-like material
0:22:30 > 0:22:31called keratin.
0:22:33 > 0:22:36The female's spurs can be 25% larger than the male's.
0:22:40 > 0:22:44And for good reason. They use their spurs in battles, to control access
0:22:44 > 0:22:46to breeding males.
0:22:47 > 0:22:50So, Jacanas actually teach us a lot about the evolution
0:22:50 > 0:22:52of animal weapons.
0:22:52 > 0:22:55They show us that, when the roles are reversed,
0:22:55 > 0:22:56then the weapons are backwards, too.
0:22:56 > 0:22:59Competition, in this case, is stronger in females.
0:22:59 > 0:23:02They're the ones with the bigger weapons.
0:23:02 > 0:23:04And in some Jacanas,
0:23:04 > 0:23:07that role reversal has surprisingly cruel consequences.
0:23:09 > 0:23:10If a male is left alone,
0:23:10 > 0:23:13a new female will not hesitate to press her advantage.
0:23:16 > 0:23:17Claiming the territory...
0:23:19 > 0:23:20..the lone male...
0:23:24 > 0:23:27..and obliterating the previous female's unhatched chicks.
0:23:32 > 0:23:36And this is, sort of, a horrendous thing to think about.
0:23:36 > 0:23:39Basically, she is now destroying his eggs.
0:23:43 > 0:23:46- She wipes the slate clean. - Exactly.- So how much faster?
0:23:46 > 0:23:48If he's on eggs like that one where she destroyed the eggs,
0:23:48 > 0:23:50she's basically saved herself two months.
0:23:51 > 0:23:56This brutal act means that the male is now available to breed and raise
0:23:56 > 0:23:57the new female's chicks.
0:23:59 > 0:24:01She gains a reproductive male.
0:24:01 > 0:24:03With his eggs destroyed,
0:24:03 > 0:24:05this male now has no choice but to mate with the female
0:24:05 > 0:24:07who killed his offspring.
0:24:09 > 0:24:12Jacanas may not have the biggest weapons...
0:24:13 > 0:24:17..but they show that, even when the roles of the sexes are reversed,
0:24:17 > 0:24:20if the conditions are right, an arms race can begin.
0:24:29 > 0:24:32Many animals compete intensely to defend resources.
0:24:32 > 0:24:35Like a territory, food or access to a mate.
0:24:48 > 0:24:50They engage in free-for-all brawls.
0:24:53 > 0:24:55Yet these species do not have extreme weapons.
0:24:57 > 0:25:00So, something else, another condition,
0:25:00 > 0:25:02must be needed to kick-start their evolution.
0:25:08 > 0:25:12To find the answer, Doug turns to dung.
0:25:12 > 0:25:14More specifically, the beetles that depend on it.
0:25:15 > 0:25:17When you look at something like dung beetles,
0:25:17 > 0:25:20they're literally competing for the same piles of dung.
0:25:20 > 0:25:23And yet some of those beetles have these huge, spectacular weapons
0:25:23 > 0:25:25and others have nothing at all.
0:25:26 > 0:25:28There's two kinds of dung beetles.
0:25:28 > 0:25:30There's the kind of dung beetle that carves the balls and rolls
0:25:30 > 0:25:33them away. Class one, the ball rollers.
0:25:35 > 0:25:38The ball rollers collect dung and move it to a safe place,
0:25:38 > 0:25:40to raise their families.
0:25:41 > 0:25:44Sometimes, there's a chaotic melee for control of a dung ball.
0:25:45 > 0:25:48But these ball rollers don't battle with weapons.
0:25:49 > 0:25:50They are unarmed.
0:25:52 > 0:25:55Then, there's this other type of dung beetle that had been
0:25:55 > 0:25:58less well studied. Those are what we call the tunnellers.
0:25:58 > 0:26:01Significantly, the tunnellers have big horns.
0:26:02 > 0:26:03They don't roll the dung.
0:26:08 > 0:26:11Instead, they dig straight underneath it.
0:26:12 > 0:26:14So, why have the tunnellers entered an arms race,
0:26:14 > 0:26:16when their close cousins have not?
0:26:18 > 0:26:21Doug set up a viewing system, to see what the tunnellers were doing
0:26:21 > 0:26:23beneath the surface.
0:26:23 > 0:26:27He had to use red lights, to avoid disrupting their natural behaviour.
0:26:28 > 0:26:31The missing piece to the story was what happened underground.
0:26:32 > 0:26:35Females dig tunnels beneath the piles of dung,
0:26:35 > 0:26:38stashing it into these little brood balls, they're called,
0:26:38 > 0:26:40and then she'd lay an egg very carefully at the end
0:26:40 > 0:26:41of each one of these.
0:26:41 > 0:26:46The males plant themselves at the entrance to one of these tunnels.
0:26:46 > 0:26:49They've got hooks and spines on their legs that they can wedge into
0:26:49 > 0:26:52the soil. They use their horns in fights with rival males.
0:26:52 > 0:26:56They face out and any rival male that tries to get access to that
0:26:56 > 0:26:59female's got to push past the guarding male.
0:27:00 > 0:27:02And that's when fights break out.
0:27:04 > 0:27:08Until Doug captured this rare, low-resolution footage 20 years ago,
0:27:08 > 0:27:10nobody even knew these beetles fought.
0:27:13 > 0:27:17The males use their shovel-like heads and sharp horns as weapons,
0:27:17 > 0:27:20in brutal battles to control the female's brooding tunnels.
0:27:22 > 0:27:26These beetles will walk right by each other on the surface and not
0:27:26 > 0:27:28even bump each other. They couldn't care less.
0:27:28 > 0:27:31But put them in a tunnel and, just like that, you've got a war.
0:27:32 > 0:27:36Any rival males have to enter one at a time and they pretty much have
0:27:36 > 0:27:38to face their opponent face-to-face.
0:27:40 > 0:27:43The difference between the two types of dung beetle was that
0:27:43 > 0:27:45the ball rollers fought in scrambles...
0:27:46 > 0:27:49..whilst the tunnellers,
0:27:49 > 0:27:52stuck in a confined space, were fighting in face-to-face battles.
0:27:54 > 0:27:55They were duelling.
0:28:00 > 0:28:03Doug wondered if one-on-one duels could be found in other species
0:28:03 > 0:28:04with extreme weapons.
0:28:07 > 0:28:10Chameleons have to be one of my favourite animals of all time.
0:28:18 > 0:28:20They are the quintessential ambush predator.
0:28:20 > 0:28:23They sit tight, they can change the colour of their skin,
0:28:23 > 0:28:25their eyes can swivel in different directions,
0:28:25 > 0:28:27so they move independently.
0:28:28 > 0:28:32And, they have this fantastic ambush weapon,
0:28:32 > 0:28:35so they can thwap out there with their tongue.
0:28:35 > 0:28:38A chameleon's tongue is able to extend, like a telescope,
0:28:38 > 0:28:40to twice the length of its body.
0:28:47 > 0:28:49Wow! Look at that! Out of nowhere.
0:28:51 > 0:28:56It can accelerate from zero to 60mph in one-hundredth of a second.
0:28:58 > 0:29:01But there's another kind of weapon in, at least, some chameleons.
0:29:01 > 0:29:05It's this other kind of weapon that I get excited about.
0:29:05 > 0:29:08Even though all chameleons are closely related,
0:29:08 > 0:29:11only a few have big horns on their faces.
0:29:12 > 0:29:13There is a set of weapons.
0:29:13 > 0:29:16These guys look like little dinosaurs.
0:29:16 > 0:29:19Like a triceratops, with the horns coming forward from the head.
0:29:20 > 0:29:23Male Jackson's chameleons use their horns to battle one another
0:29:23 > 0:29:26on branches, over access to females.
0:29:26 > 0:29:28Think of this like Jurassic Park jousting,
0:29:28 > 0:29:32as these males push and pry and try to twist each other off the branch.
0:29:36 > 0:29:39So, it turns out it's the details of the fight that matters.
0:29:41 > 0:29:44If you look at this fight,
0:29:44 > 0:29:46they're approaching each other face-to-face.
0:29:46 > 0:29:50They're locking horns. They're pushing, they're straining.
0:29:50 > 0:29:54Just like the tunnelling beetles, the chameleons are duelling.
0:29:54 > 0:29:59It's no accident that, for 5,000 years of recorded human history,
0:29:59 > 0:30:01the only sort of fight that has ever
0:30:01 > 0:30:04mattered for honour or status was the duel.
0:30:04 > 0:30:07Ritualised, repeatable and fair.
0:30:07 > 0:30:12When males face off one-on-one in a duel, males with bigger weapons win.
0:30:18 > 0:30:20So, this was that final ingredient.
0:30:21 > 0:30:24The third - the missing - ingredient was duels.
0:30:25 > 0:30:29Doug's discovery was the final piece of the evolutionary jigsaw.
0:30:31 > 0:30:33Fights must be a face-to-face duel.
0:30:41 > 0:30:44Only when animals fight in these ritualised duels do the benefits
0:30:44 > 0:30:46of extreme weapons outweigh the costs.
0:30:55 > 0:30:58What I'm suggesting is that, when these three conditions are met -
0:30:58 > 0:31:03intense competition, defendable resources and duels -
0:31:03 > 0:31:07selection for big weapons becomes so strong that it eclipses any costs
0:31:07 > 0:31:09associated with these structures.
0:31:09 > 0:31:11Nothing else matters.
0:31:14 > 0:31:17Launching their populations onto trajectories
0:31:17 > 0:31:18of explosive weapon evolution.
0:31:21 > 0:31:24Most forms of life on Earth do not have extreme weapons.
0:31:29 > 0:31:32The rare species that do come from a diverse range of different
0:31:32 > 0:31:33animal families.
0:31:35 > 0:31:39Doug's theory describes three simple conditions that unites them all.
0:31:42 > 0:31:44A resource that's defendable...
0:31:45 > 0:31:47..competition with a rival...
0:31:48 > 0:31:51..and fights that take place as one-on-one duels.
0:31:55 > 0:31:56And in the animal kingdom...
0:31:57 > 0:32:00..when those three conditions are present...
0:32:00 > 0:32:02extreme weapons can evolve.
0:32:19 > 0:32:22But there are sometimes exceptions to rules.
0:32:28 > 0:32:29The most iconic example...
0:32:31 > 0:32:33..is an ancient, extinct beast.
0:32:42 > 0:32:44We're looking at a fossil of a sabre-tooth cat.
0:32:44 > 0:32:45This is the actual fossil.
0:32:45 > 0:32:49It's not a cast. The animal probably lived in California
0:32:49 > 0:32:51about a million years ago.
0:32:53 > 0:32:56Sabre-tooths actually teach us an awful lot about animal weapons.
0:32:56 > 0:32:59For one thing, you can't miss the teeth, right?
0:32:59 > 0:33:00I mean, the teeth are huge.
0:33:00 > 0:33:02But that's actually an interesting problem in itself,
0:33:02 > 0:33:05because this is a predator.
0:33:07 > 0:33:10The primary use for a sabre-tooth's colossal canines is thought to be
0:33:10 > 0:33:13for hunting, not securing a mate.
0:33:17 > 0:33:19This is why sabre-tooths are so exciting.
0:33:19 > 0:33:22They're the exception.
0:33:22 > 0:33:25It's the manner in which they caught their prey that explains why they
0:33:25 > 0:33:26evolved extreme weapons.
0:33:28 > 0:33:31Sabre-tooths are special because they're ambush predators.
0:33:35 > 0:33:39Imagine what it would be like to get chomped on by something like that.
0:33:41 > 0:33:44They sit and wait and then lunge out with a quick strike,
0:33:44 > 0:33:46to grab unsuspecting prey.
0:33:48 > 0:33:52For most predators, heavy armouries are simply too bulky.
0:33:52 > 0:33:53They'd slow them down.
0:33:57 > 0:34:00But, for ambush predators that strike quickly,
0:34:00 > 0:34:03the evolution of big weaponry makes sense.
0:34:11 > 0:34:13It works under the ocean, for things like mantis shrimp
0:34:13 > 0:34:14and pistol shrimp.
0:34:17 > 0:34:19It works for ant lions.
0:34:22 > 0:34:23It works even for those crazy,
0:34:23 > 0:34:27deep sea angler fish that are essentially a big jaw with a tail.
0:34:28 > 0:34:31These guys had lures that they would dangle in front of them, that would
0:34:31 > 0:34:32pull the prey into them.
0:34:33 > 0:34:35Ambush predators use their extreme weapons
0:34:35 > 0:34:37to capture and kill their prey.
0:34:40 > 0:34:43But the majority of animals which have entered an arms race
0:34:43 > 0:34:44aren't hunters.
0:34:46 > 0:34:48All of the rest of the species with big weapons.
0:34:48 > 0:34:51Species with the biggest and the craziest things sticking off
0:34:51 > 0:34:53of their bodies, those animals are using
0:34:53 > 0:34:55their weapons for reproduction.
0:34:58 > 0:35:01These creatures use their weapons to fight each other.
0:35:04 > 0:35:06You might imagine that their epic clashes
0:35:06 > 0:35:07result in many lethal injuries.
0:35:15 > 0:35:18But animals with extreme weapons use them in a manner that means,
0:35:18 > 0:35:22win or lose, the likelihood is that you will survive the fight.
0:35:26 > 0:35:29The very nature of a duel means that there are rules of engagement.
0:35:31 > 0:35:36These species fight head-to-head, weapon-to-weapon,
0:35:36 > 0:35:39which means they're less likely to be fatally gouged or gored to death.
0:35:44 > 0:35:47For the ultimate test of this principle,
0:35:47 > 0:35:49Doug is travelling to Washington State.
0:35:57 > 0:35:59He's come to see the animal weapons record holder.
0:36:04 > 0:36:07Hi. Can I see the biggest weapon in the animal world?
0:36:07 > 0:36:09Sure.
0:36:12 > 0:36:16- Here it is. - That's it? It's not very big.
0:36:16 > 0:36:19So, these are fiddler crabs. Ow!
0:36:20 > 0:36:23Maybe it's a little bit bigger than I thought. So, this is it.
0:36:24 > 0:36:25The record-holder.
0:36:27 > 0:36:31So, it may be a small crab, but this claw, the weapon,
0:36:31 > 0:36:32can be half of its body mass.
0:36:32 > 0:36:35The claw can weigh as much as the whole rest of the crab.
0:36:35 > 0:36:39It would be like you walking around carrying my whole body weight as one
0:36:39 > 0:36:41- of your arms.- That's incredible.
0:36:42 > 0:36:45Fiddler crab claws are proportionately bigger than any
0:36:45 > 0:36:46other known animal weapon on earth.
0:36:48 > 0:36:52There's about 103 different species of fiddler crabs.
0:36:52 > 0:36:55They live all over the world in the Tropics and they eat algae
0:36:55 > 0:36:57off the surface of the mud.
0:36:58 > 0:37:01Brook Swanson investigates the surprising advantages of these
0:37:01 > 0:37:04super weapons at his fiddler crab lab.
0:37:05 > 0:37:07So, females have two little claws.
0:37:08 > 0:37:12They can actually eat twice as fast as the males.
0:37:12 > 0:37:15The males only have these giant claws...
0:37:17 > 0:37:19..and can't use their weapon claw to eat.
0:37:20 > 0:37:23Right, he's bitten me three times already.
0:37:23 > 0:37:25Can you show me what these guys can do?
0:37:25 > 0:37:27Absolutely. We can use this force
0:37:27 > 0:37:31meter to measure how strong their claws are.
0:37:31 > 0:37:33This just measures how hard they squeeze.
0:37:33 > 0:37:37Exactly. You put their claw right there.
0:37:37 > 0:37:39- There you go.- They squeeze.
0:37:40 > 0:37:41That's about 20 Newtons.
0:37:41 > 0:37:44So, the crab is producing about 20 Newtons with its claw.
0:37:45 > 0:37:475lbs of force.
0:37:47 > 0:37:52So, like having a bag of sugar on a pin pushing on you.
0:37:52 > 0:37:55So, it's not just 5lbs, it's 5lbs concentrated on a very sharp point.
0:37:55 > 0:37:58- Exactly. - That's why it hurts so much.
0:38:00 > 0:38:01Crab claws have enough power
0:38:01 > 0:38:03to slice straight through a rival's shell.
0:38:06 > 0:38:09So, they're plenty strong enough to kill each other,
0:38:09 > 0:38:11but when we keep them in the lab,
0:38:11 > 0:38:15we hardly ever see them fighting and I've never seen one kill another one
0:38:15 > 0:38:18in a lab. When you study these in the field,
0:38:18 > 0:38:20it's very rare to see them fighting there, as well.
0:38:22 > 0:38:26So, if they hardly ever use their giant claws to fight,
0:38:26 > 0:38:27what do the male crabs use them for?
0:38:29 > 0:38:32So, here we have two male fiddler crabs.
0:38:32 > 0:38:35And their body size is about the same.
0:38:35 > 0:38:36But, if you look at their claws...
0:38:36 > 0:38:39- It's huge.- ..the claw's twice as big as the other one.
0:38:39 > 0:38:41Wow, that is so obvious!
0:38:41 > 0:38:43What they spend most of their time doing is not fighting with these
0:38:43 > 0:38:45claws, but waving them in the air.
0:38:48 > 0:38:51So, they walk around on the sand and they wave the claw
0:38:51 > 0:38:54and wave the claw and wave the claw.
0:38:54 > 0:38:58And they're signalling to the other crabs how big and how strong
0:38:58 > 0:38:59they are.
0:39:00 > 0:39:03And so, if you're looking at crabs by their claws,
0:39:03 > 0:39:05you can easily tell the difference.
0:39:05 > 0:39:09You can easily tell that this crab is bigger and stronger and a better
0:39:09 > 0:39:12fighter. That's what makes the claw a good signal.
0:39:12 > 0:39:14This is awesome. This is just like what we see in other animals.
0:39:14 > 0:39:17You'd think the species with the really big weapons would use them
0:39:17 > 0:39:20to fight all the time. And yet, what we see is the reverse.
0:39:20 > 0:39:23That the species with the biggest weapons are actually
0:39:23 > 0:39:24the most peaceful.
0:39:29 > 0:39:32Paradoxically, it is uncommon for most animals
0:39:32 > 0:39:34with extreme weapons to fight.
0:39:37 > 0:39:40Although we revel in the rare moments these creatures do clash...
0:39:42 > 0:39:46..in the natural world, confrontations seldom escalate into
0:39:46 > 0:39:47head-to-head, brute force combat.
0:39:51 > 0:39:53When rival males meet,
0:39:53 > 0:39:56they will often avoid fighting, by measuring the prowess of their
0:39:56 > 0:39:58opponent, using ritualised behaviours.
0:40:01 > 0:40:04Elk males do this by strutting in parallel lines,
0:40:04 > 0:40:05to assess the competition.
0:40:09 > 0:40:11ELEPHANT BELLOWS
0:40:12 > 0:40:16Nearly all these encounters end without a single blow being dealt.
0:40:22 > 0:40:26So, we've gone from what was essentially a blunt-force weapon
0:40:26 > 0:40:30to something that we now realise is a whole lot more than that.
0:40:30 > 0:40:33The rival males are backing away, without even challenging them
0:40:33 > 0:40:34in open battle.
0:40:34 > 0:40:38These biggest weapons of all are acting as a deterrent,
0:40:38 > 0:40:42settling dangerous contests without actual battle.
0:40:42 > 0:40:46These fiddler crabs have a weapon so deadly that attacking
0:40:46 > 0:40:49an equally-armed adversary could be suicidal.
0:40:52 > 0:40:54In the animal kingdom,
0:40:54 > 0:40:57the most powerful weapons are also the most effective deterrents.
0:41:06 > 0:41:08So, I've been to some amazing places in my search for extreme
0:41:08 > 0:41:13animal weapons. The place I'm going now is the strangest of all.
0:41:13 > 0:41:15The weapons we're going to look at today
0:41:15 > 0:41:18are both exciting and terrifying.
0:41:19 > 0:41:22Doug has long wondered if what applies to the animal arms race
0:41:22 > 0:41:24can be applied to our own.
0:41:35 > 0:41:39Ross Millard is a captain at Malmstrom Air Force Base in Montana.
0:41:55 > 0:41:56Can you tell me about the base?
0:41:56 > 0:41:59Absolutely. We're here at Malmstrom Air Force Base.
0:41:59 > 0:42:03We are one of three missile bases in Air Force Global Strike Command.
0:42:03 > 0:42:06Our ultimate weapon here is the Minuteman-III nuclear missile.
0:42:06 > 0:42:07- The big one?- Yes.
0:42:08 > 0:42:11The Minuteman-III is an intercontinental ballistic missile
0:42:11 > 0:42:14that can be armed with a nuclear warhead.
0:42:15 > 0:42:18These are the most destructive weapons on earth.
0:42:19 > 0:42:23So, what can you tell me about the capability of these missiles?
0:42:23 > 0:42:28The missile itself will take the warhead 7,000 miles and produce
0:42:28 > 0:42:29a nuclear detonation.
0:42:31 > 0:42:33Other than that, I can't get into
0:42:33 > 0:42:35great detail on the power of the weapon...
0:42:35 > 0:42:38- OK, fair enough. - ..the specific characteristics.
0:42:38 > 0:42:40- But it's powerful? - Yes. Not just powerful,
0:42:40 > 0:42:42but designed and intended to work.
0:42:43 > 0:42:45There are 150 of these missiles
0:42:45 > 0:42:48ready to launch from bunkers in the 13,000 square miles
0:42:48 > 0:42:50surrounding the base.
0:42:52 > 0:42:54Captain Millard is taking Doug
0:42:54 > 0:42:56to the missile launch training facility.
0:42:57 > 0:42:59So, they are actually at different depths.
0:42:59 > 0:43:02Some of them are a little more shallow,
0:43:02 > 0:43:05just depending on the topography and the terrain.
0:43:11 > 0:43:12Wow! I can't believe I'm in here.
0:43:14 > 0:43:17From protected subterranean control centres,
0:43:17 > 0:43:20missileers can fire the nuclear warheads.
0:43:20 > 0:43:22All right. So, what does this console do?
0:43:22 > 0:43:23Essentially, it allows
0:43:23 > 0:43:26the crew members to be able to exercise command
0:43:26 > 0:43:28over all the missiles that are assigned to them.
0:43:28 > 0:43:29So, each control centre
0:43:29 > 0:43:32is responsible for ten missiles, on this screen,
0:43:32 > 0:43:35or on the far right-hand screen over there.
0:43:35 > 0:43:38So, what would you say the primary function of these weapons is?
0:43:38 > 0:43:41Day-to-day, the primary function is to provide a deterrence factor,
0:43:41 > 0:43:45to let our adversaries know we have this capability.
0:43:45 > 0:43:47But it's an interesting paradox for the system, because we don't want to
0:43:47 > 0:43:50use it. But, if we have to use it, we have to know that it works
0:43:50 > 0:43:52- as well, too. - It's exactly the same in animals.
0:43:52 > 0:43:54That do almost exactly the same thing.
0:43:54 > 0:43:55You find the biggest, the craziest,
0:43:55 > 0:43:58the most extreme animal weapons always work as deterrents, too.
0:44:01 > 0:44:03If you're a male with the smaller weapons,
0:44:03 > 0:44:05it often pays to assess the situation
0:44:05 > 0:44:07and turn around and walk away.
0:44:10 > 0:44:13All extreme weapons work as deterrents.
0:44:16 > 0:44:19And the similarities do not end there.
0:44:19 > 0:44:22One of the other parallels we see with animals is that when
0:44:22 > 0:44:24the weapons get really, really big,
0:44:24 > 0:44:30then only a few individuals in the population can afford them.
0:44:30 > 0:44:34Realistically, how many countries could possibly afford to have
0:44:34 > 0:44:36the infrastructure, the capabilities,
0:44:36 > 0:44:38that we're talking about with a nuclear deterrence triad?
0:44:38 > 0:44:42Very few. It's not that simple just because you have the missile.
0:44:42 > 0:44:44There's all sorts of infrastructure.
0:44:44 > 0:44:46There's the warhead, there's the support equipment,
0:44:46 > 0:44:50there's all sorts of various increments along the way that add
0:44:50 > 0:44:54to the complexity. The whole nuclear enterprise is much more expensive
0:44:54 > 0:44:56than just one missile.
0:44:57 > 0:45:00The costs associated with owning these weapons is phenomenal.
0:45:02 > 0:45:04Of all the nations in the world,
0:45:04 > 0:45:06only nine are thought to control nuclear warheads.
0:45:08 > 0:45:11I just have to say again that that is exactly the same as what we see
0:45:11 > 0:45:13in animals. It's exactly the same.
0:45:13 > 0:45:17The reason the really big weapons work in animals is that they're so
0:45:17 > 0:45:19unbelievably expensive that almost nobody can afford them.
0:45:19 > 0:45:22That's part of why they work as a deterrent
0:45:22 > 0:45:24is the best condition, the biggest bulls and bucks,
0:45:24 > 0:45:27those are the only animals that can afford the really big weapons.
0:45:29 > 0:45:33Captain Millard has agreed to show Doug a launch sequence.
0:45:33 > 0:45:36So, we will launch the missiles, but the person who has the authority
0:45:36 > 0:45:38is the President.
0:45:38 > 0:45:41So, up in this container here, that one right there.
0:45:41 > 0:45:43If you open it up, there's going to be a key in there,
0:45:43 > 0:45:45as well as authenticators.
0:45:46 > 0:45:49For Doug, there are parallels between the development of our own
0:45:49 > 0:45:53super weapons and the evolution of the biggest weapons in nature.
0:45:55 > 0:45:58So, manufactured weapons aren't parts of our bodies,
0:45:58 > 0:46:00like tusks or horns.
0:46:00 > 0:46:03Instructions for their construction aren't encoded in DNA.
0:46:05 > 0:46:07But their form's changed through time, in much the same way
0:46:07 > 0:46:11- as animal weapons. - And go ahead and slide down.
0:46:13 > 0:46:15When the conditions are just right,
0:46:15 > 0:46:18manufactured weapons can get caught up in arms races, too.
0:46:18 > 0:46:21Insert the launch key and, on my count, we'll turn and hold.
0:46:23 > 0:46:26Surging forward to bigger and bigger sizes.
0:46:26 > 0:46:30Deadlier, faster and vastly more expensive.
0:46:30 > 0:46:33Three, two, one, turn.
0:46:33 > 0:46:35Hold...and release.
0:46:48 > 0:46:52If Doug's theory is right, all extreme weapons, human or animal,
0:46:52 > 0:46:55evolve over time under the same conditions.
0:46:57 > 0:46:59They cost an enormous amount of resources.
0:47:01 > 0:47:03And their primary function is as a deterrent.
0:47:10 > 0:47:13So, is there anything that can undermine the animals
0:47:13 > 0:47:15with the most extreme weapons?
0:47:18 > 0:47:20Doug was studying dung beetles,
0:47:20 > 0:47:22when he discovered that the smaller males,
0:47:22 > 0:47:26without the largest weapons, had found a sneaky way to reproduce.
0:47:28 > 0:47:31So, one of the things that we were able to learn from these beetles
0:47:31 > 0:47:33is that the little beetles cheat.
0:47:35 > 0:47:38Doug already knew that males with big weapons guard the entrances
0:47:38 > 0:47:40to female tunnels.
0:47:40 > 0:47:42If you're another big beetle,
0:47:42 > 0:47:45you can challenge him in outright open battle but, if you're tiny,
0:47:45 > 0:47:46you don't stand a chance.
0:47:47 > 0:47:50So, instead of fighting a losing battle,
0:47:50 > 0:47:54they go right next to a tunnel and they start to dig their own tunnel.
0:47:55 > 0:47:59They mine their way into the tunnel, come in beneath the guarding male,
0:47:59 > 0:48:01go straight down to the female, find the female, mate with the female,
0:48:01 > 0:48:02turn around and leave.
0:48:05 > 0:48:08This small, sneaky male has found a way to evade the guard
0:48:08 > 0:48:10and mate with the prized female.
0:48:13 > 0:48:15Then he escapes up his own secret tunnel.
0:48:17 > 0:48:18Big males have the weapons.
0:48:18 > 0:48:21The big males fight the conventional battles.
0:48:21 > 0:48:23The little guys break the rules.
0:48:24 > 0:48:28The same cunning tactics can be seen in other species.
0:48:31 > 0:48:33So, consider the cuttlefish.
0:48:35 > 0:48:38In cuttlefish, you get all these little tiny males, these wimpy,
0:48:38 > 0:48:42tiny runts. There's no way they would win, if they tried to fight
0:48:42 > 0:48:44by the rules.
0:48:45 > 0:48:48Big dominant males guard fertile females.
0:48:50 > 0:48:54If an evenly-matched contender challenges him, occasionally,
0:48:54 > 0:48:56they battle one another with sharp beaks and tentacles.
0:48:58 > 0:49:02I would not want to get caught up in a tangle with one of these guys!
0:49:02 > 0:49:06The winners hover above the females they want to mate with.
0:49:06 > 0:49:08So, now we've got another cuttlefish coming up.
0:49:08 > 0:49:10This one looks like a female...
0:49:12 > 0:49:14..but it's not a female.
0:49:14 > 0:49:17If you look closely, this is actually a tiny male...
0:49:18 > 0:49:21..but he's cloaked himself in colours that make him
0:49:21 > 0:49:22look like a female,
0:49:22 > 0:49:26so he can come right up to the guarding male unmolested.
0:49:28 > 0:49:31The sneaky male works his way right on in there and,
0:49:31 > 0:49:34by looking and acting like a female,
0:49:34 > 0:49:35he is able to get into a position
0:49:35 > 0:49:38where he can breed with the female, too.
0:49:40 > 0:49:43This female's eggs will be a mix of some massive macho male's
0:49:43 > 0:49:45and some tiny trickster's.
0:49:56 > 0:49:58These tactics are so pervasive
0:49:58 > 0:50:00that Doug can even find cheats in Montana.
0:50:03 > 0:50:06Jack Hogg is a bighorn sheep biologist.
0:50:07 > 0:50:11He is taking Doug to search an island on Flathead Lake, to observe
0:50:11 > 0:50:13their alternative tactics.
0:50:21 > 0:50:22Bighorn sheep are famous for
0:50:22 > 0:50:25engaging in epic, ritualised battles.
0:50:28 > 0:50:31During the rut, rival males size each other up.
0:50:36 > 0:50:38Occasionally, when it's an even match...
0:50:39 > 0:50:40..they fight.
0:50:48 > 0:50:50Through a series of horn-to-horn clashes,
0:50:50 > 0:50:52the rams establish a hierarchy.
0:50:55 > 0:50:57The winners become the dominant males.
0:51:04 > 0:51:08During the breeding season, the victors guard fertile females.
0:51:10 > 0:51:16Largest horned, largest bodied rams search for, and defend, ewes during
0:51:16 > 0:51:19- their fertile period.- So the biggest males with the biggest weapons,
0:51:19 > 0:51:23their strategy is to guard access to the females for that one day
0:51:23 > 0:51:26when they're fertile.
0:51:26 > 0:51:29Jack's discovered that the subordinate males have their
0:51:29 > 0:51:30own cunning mating strategy.
0:51:32 > 0:51:34He calls it coursing.
0:51:34 > 0:51:36The coursing strategy, in essence,
0:51:36 > 0:51:39is to do whatever it takes to evade
0:51:39 > 0:51:42the defence of a socially-dominant ram
0:51:42 > 0:51:44who's defending a female during her fertile period,
0:51:44 > 0:51:48but it's whatever needs to be done, whatever dirty trick,
0:51:48 > 0:51:49to force a mating.
0:51:53 > 0:51:56The dominant male here is called Crud Horn.
0:51:59 > 0:52:01He's guarding a fertile female.
0:52:04 > 0:52:08The fertile female has a white spot, so we're calling her White Neck.
0:52:15 > 0:52:17A large group of subordinate males
0:52:17 > 0:52:20are watching White Neck's every move.
0:52:22 > 0:52:24They want to mate with her,
0:52:24 > 0:52:26but Crud Horn is guarding her closely.
0:52:29 > 0:52:32So Crud Horn has two important tasks in front of him.
0:52:32 > 0:52:36One is to mate with her during her fertile period,
0:52:36 > 0:52:40but he also has to defend the female against any male who wishes
0:52:40 > 0:52:42to breed with her.
0:52:48 > 0:52:52Typically, females run away from this group of large bodies that are
0:52:52 > 0:52:55interacting. It's a dangerous place to be, so they run away,
0:52:55 > 0:52:56and that's what creates the chase.
0:53:17 > 0:53:20White Neck wants to escape the rush of coursing males.
0:53:24 > 0:53:27Crud Horn is trying to keep up with her
0:53:27 > 0:53:29and deflect the subordinate males during the chase.
0:53:33 > 0:53:36Crud Horn's defence, actually, is extraordinary.
0:53:36 > 0:53:37It's very good.
0:53:39 > 0:53:42He's very physical, in terms of clashing and pushing and shoving
0:53:42 > 0:53:44the other rams.
0:53:45 > 0:53:48But, every once in a while, one of these coursers
0:53:48 > 0:53:50will succeed in forcing a breeding.
0:54:00 > 0:54:01One coursing male attempts to mate
0:54:01 > 0:54:03with White Neck while she's separated
0:54:03 > 0:54:05from Crud Horn in the scramble.
0:54:05 > 0:54:08- That's all it takes, a few seconds?- A few seconds.
0:54:08 > 0:54:11The coursing male now could have a chance of fathering
0:54:11 > 0:54:13White Neck's offspring.
0:54:18 > 0:54:20By trying to mate with the female while running,
0:54:20 > 0:54:23even for just a mere moment,
0:54:23 > 0:54:24the coursing male has used
0:54:24 > 0:54:27a tactic unrelated to the size of his weapons.
0:54:28 > 0:54:31This is clever, in a way. It's almost like they are able to use
0:54:31 > 0:54:33the bulk and the weight and the size
0:54:33 > 0:54:36of the weapons of the alpha males against them...
0:54:37 > 0:54:40..by getting them to lunge in a particular direction and then
0:54:40 > 0:54:42taking advantage of being smaller and agile.
0:54:44 > 0:54:47So, if all these males are using these alternative strategies,
0:54:47 > 0:54:50is it even worth being the big alpha male?
0:54:50 > 0:54:51- They do better. - They still do better?
0:54:51 > 0:54:54They have more babies, basically. A high-ranking male,
0:54:54 > 0:54:59he would be the father of 60% of the lambs produced
0:54:59 > 0:55:01by the females he defends.
0:55:01 > 0:55:05The dominant male, the male with the biggest horns,
0:55:05 > 0:55:06still fathers far more offspring
0:55:06 > 0:55:08than all of the coursing males combined.
0:55:12 > 0:55:14To the victor go the spoils.
0:55:14 > 0:55:16We see this in every one of these animal systems,
0:55:16 > 0:55:17that the biggest males are the ones
0:55:17 > 0:55:20that can afford to produce the biggest weapons
0:55:20 > 0:55:23and these males win, in every sense of the word.
0:55:28 > 0:55:32Today, perhaps the biggest risk for many animals with extreme weapons
0:55:32 > 0:55:33doesn't come from cheats.
0:55:36 > 0:55:38It comes from a much more modern threat.
0:55:41 > 0:55:45Weapon sizes in some populations of animals,
0:55:45 > 0:55:47including bighorn sheep,
0:55:47 > 0:55:51elephants and caribou,
0:55:51 > 0:55:53are decreasing,
0:55:53 > 0:55:55and the trigger for this change...
0:55:57 > 0:55:58..is us.
0:56:00 > 0:56:03Human trophy hunters prize the biggest tusks...
0:56:04 > 0:56:08..horns and antlers.
0:56:09 > 0:56:12Trophy hunting removes the genes for the biggest weapons.
0:56:15 > 0:56:17In one elephant population,
0:56:17 > 0:56:22the average tusk size was reduced by 40% in just 25 years.
0:56:25 > 0:56:26And in another population,
0:56:26 > 0:56:30the number of tuskless individuals increased by over 20%.
0:56:34 > 0:56:37We have tipped the balance of these animal arms races.
0:56:47 > 0:56:48Despite the human hunters...
0:56:50 > 0:56:52..enormous biological costs...
0:56:53 > 0:56:56..and being sabotaged by cheats...
0:56:57 > 0:56:59..for animals in an arms race,
0:56:59 > 0:57:01the males with the biggest and most extreme weapons
0:57:01 > 0:57:03are the most successful.
0:57:07 > 0:57:10These individuals are winning the evolutionary war.
0:57:12 > 0:57:13They are not wiping themselves out.
0:57:19 > 0:57:22And maybe that's a vital lesson for us.
0:57:26 > 0:57:28ELEPHANT TRUMPETS
0:57:37 > 0:57:39So this has been quite a journey for me -
0:57:39 > 0:57:42a ride more wild than I ever could have imagined.
0:57:42 > 0:57:46So, although most animal species don't have big weapons,
0:57:46 > 0:57:50these extremes have arisen many different times independently
0:57:50 > 0:57:52within separate lineages of animals.
0:57:57 > 0:57:59What's the same, though,
0:57:59 > 0:58:02are the conditions that are necessary in order to launch
0:58:02 > 0:58:05that population into an arms race.
0:58:08 > 0:58:11Who would have thought that the battles of beetles held lessons
0:58:11 > 0:58:12for weapons everywhere?
0:58:14 > 0:58:16Extreme weapons are extreme weapons.
0:58:16 > 0:58:18Animal, human - it does not matter.
0:58:18 > 0:58:20Their biology is exactly the same.
0:58:21 > 0:58:25ELEPHANTS TRUMPET