Nature's Wildest Weapons: Horns, Tusks and Antlers Natural World

More than eight million animal species live on the planet today.

Only a special few are armed with extreme weapons.

Huge physical appendages growing from their bodies.

Look at that set of antlers, wow!

Wielded in titanic battles.

What gives rise to these enormous structures?

When the conditions are just right,

these weapons can get caught up in arms races.

Are they more than just instruments of blunt force?

Can you show me the biggest weapon in the animal world?

Absolutely.

And what can their evolution teach us about our own arms race?

Three, two, one, turn.

In south-west Montana is a bizarre armoury...

..created from a collection of naturally-shed antlers.

Oh, my God!

Wow!

Unbelievable.

Doug Emlen is a professor of biology.

He spent his lifetime trying to unlock the secrets

of extreme animal weapons.

Look at this!

This is an antler from an elk, a bull elk from here in Montana.

This is 20lbs of bone.

And they, of course, produce two of them every year.

Antlers are the fastest-growing bones

described from any living vertebrae.

Nature's armoury is diverse...

..horns...

..tusks...

..stings.

They can be used for attack...

..or for protection.

Almost any animal has a weapon, of one sort or another.

I mean, cats have claws, eagles have talons,

even dogs have a respectable set of teeth.

But those weapons stay small. There's nothing big or awkward

or anything that would slow these animals down.

Nothing sticking out of their bodies, in some crazy way.

But here and there, sprinkled through the tree of life,

are species where their weapons are taken to an extreme.

For me, I'm interested in the weapons of offence,

weapons that are used in fighting and, in particular,

the weapons that are big.

Those are the species that keep me awake at night.

Luckily for Doug, he can find perfect subjects

right on his doorstep in Montana.

Look at that guy.

Look at him.

Rancher Doug Averill keeps elk on his land.

Amongst them are a number of mature males.

During the autumn rut,

the antlers of these bull elk are at their most impressive.

ELK BELLOWS

Here comes another one.

They're all going to size each other up here,

when you get this many bulls together.

This might get interesting.

Fuelled by testosterone,

the biggest bulls are looking to assert their dominance.

When it's not in the rutting season, they're relatively calm,

peaceful animals. But it's kind of like a bunch of guys on Friday night

at the bar!

This is pretty rare. I haven't seen this all summer.

And you can see, they're totally locked together.

The larger bull on the right has won this round...

..but the loser still wants a fight.

He has the temperament to be an aggressive bull down the road.

It got my attention!

It's OK.

Despite being charged, Doug can't resist getting closer.

I love living in Montana and this is why.

Got two bull elks sparring behind me.

After shedding last year's rack,

the bulls have spent just six months growing this season's antlers.

Imagine the amount of resources that it takes

to produce something like this.

That would be like me producing another leg and wearing it around

on my head. They'll shed this,

they'll throw this away at the end of the season and then they have to

turn right around and start growing a whole other one again.

The only way they can grow a bone this big, this fast,

is to shunt the calcium, shunt the minerals,

away from the rest of the bones in their body.

So they're literally pulling these things out of the rest of their

skeleton and allocating it to the weapons.

They actually go through a seasonal period of osteoporosis.

The biggest bulls and bucks have brittle bones at exactly the time

of year when they're hurling themselves against each other

in all-out battles.

An antler can grow an extraordinary four centimetres a day.

The amount of energy required is huge.

Often by the end of the rut,

bulls will have lost as much as a quarter of their body weight.

They come out of that season starved and scratched

and scarred and damaged,

and they've only got a few short weeks to make up the calories

they've lost before winter or they're not going to survive.

Elk need to stay strong.

ELK BELLOWS

The weakest are the most likely to become prey.

So, imagine the predators of these guys, something like a wolf.

Wolves have to be fast, they have to be agile.

Think about what would happen to

a wolf if it had a set of antlers on the top of its head.

A wolf that awkward wouldn't be fast enough to catch

their prey. They wouldn't be able to turn quickly enough

to catch their prey.

But now if you turn around and you look at the elk, well,

it doesn't make sense there, either.

I mean, elk have to be able to escape,

they have to be able to be agile and to run fast

and antlers are going to slow them down just as much

as it slows down a wolf.

You might think that the primary function of an antler is to protect

that elk from a wolf.

But it's not. Even though a bull might be able to do some damage

with its tines...

WOLF WHIMPERS

..it's not going to be enough to save it from predation.

Considering what we know about the costs of these weapons,

why would you ever want one?

These structures are not helping the bull survive.

So what's the point of these extreme weapons?

Survivorship isn't the only game in town.

And, in fact, when it comes to evolution,

the thing that matters the most is reproduction.

Animals have evolved a multitude of weird and wonderful traits to help

them seduce a mate.

Tails...

..noses...

..even bottoms.

All can be used to attract the opposite sex.

This improves the chance that they will pass their genes on to

the next generation.

So, how do extreme weapons increase an animal's ability to reproduce?

For elk, antlers are worth the cost.

The biggest bulls with the largest antlers tend to win the most fights.

The winners mate with more females and produce the most offspring.

For animals that bear arms,

this is the evolutionary advantage extreme weapons provide.

ELK CALLS

But arms races only occur in a relatively small number of species.

So what are the conditions that spark them?

Finding the answer isn't straightforward.

Particularly when many of your subjects can't be studied in a lab.

For the kinds of things that we want to study,

it's a little difficult to raise elk in captivity.

We work on a much smaller critter.

We work on beetles.

In this particular species,

the males have a horn that's like a pitchfork that sticks forward

from the front of their heads.

And in some of the specimens, these pitchforks can be almost as long

as the whole rest of the body.

This might look small relative to an elk,

but I assure you, as far as insects are concerned, this is big.

Every bit as impressive.

It can be 30% of their body weight.

That is, literally, like you or me wearing a coffee table around on

the tops of our heads. So, imagine doing everything you do,

from waking up in the morning, to everything you do during a day,

with a coffee table fused to the top of your head.

And now you've got a little taste of what it's like to be one

of these beetles.

Doug's fascination with biology began as a young boy.

He travelled the world investigating all types of animal arms races.

Slowly, he's been piecing together evidence to explain the evolution

of extreme weapons.

So, there's an animal with an incredible weapon.

They're a different lineage of beetles from the ones that we study.

These guys live in Chile, but their story's exactly the same.

That is one of the biggest weapons of any living animal - ever.

They've got mouthparts or mandibles that have been elongated, so that

they have these curved, arcing pincers.

The males grow up to nine centimetres long.

Their specially-adapted jaws can be half their body length.

So, the males are fighting battles with rival males.

So, these are two males sparring and facing off against each other,

trying to fling each other from the tree.

For the loser, it's a long way down.

The battles between beetles offer the first clue to the special

circumstances that trigger animal arms races.

Beetles like this fight over wounds,

sort of marks or nicks on the side of a tree, where sap will ooze out

and drip down the side.

The sap attracts females, like this one.

Unlike the males, she has small jaws.

If you're a male and you can hold on to that real estate,

you have opportunities to mate with

the females when they come in to feed.

It's not an accident that castles are located on the tops of hills

or out on the ends of long moats and surrounded by water.

We've known for centuries that things that are physically isolated,

or that have restricted access, are much more economical to defend.

Exactly the same logic applies to animals.

The males that are able to win these battles or to hold on to that

territory, I mean, the ultimate prize is reproduction.

This male has fought off all his rivals.

And now he's earned the opportunity to mate with a female.

So when we start to look at these animals and say,

"What sets these species apart?

"Why do these particular species have such incredible weapons?"

The first clue, the first piece of the puzzle,

is a defendable resource against which the fights can take place.

So imagine things that whirl around in the water.

Sometimes animals are fighting over resources that can't be defended.

Think about things like raptors fighting in the air.

EAGLES SQUAWK

They'll get into these big, frenzied, acrobatic mid-air snarls.

And fights like that,

things like agility or speed are likely to matter more than

bulk and strength.

For these kinds of fights, big weapons just aren't worth the price.

A defendable resource is one of the critical requirements for an animal

arms race to begin.

And often, females are the resource.

Male hippos use their enormous teeth in fights to guard harems of females

from adversaries.

Male white rhinos use their horns to protect territories that females

travel through.

And male elephants use their tusks in combat to defend fertile females

from rivals.

I love elephants!

Each of those tusks can be, like, 100lbs of ivory.

These are huge teeth.

Bull elephant tusks are the biggest and heaviest teeth in nature.

Oh, his tusk's shattered.

OK, there you go, that's the impact that we're talking about here.

These are fantastic weapons,

partly because they're lethal in their own right,

they're able to stab, but they also allow these guys to,

like, push and strain against each other and size each other up.

There's a deeper story behind the bull's tusks.

One that's vital for all animal arms races.

Bull elephants have these massive tusks.

But if we want to understand the tusks,

we actually have to look at the females.

Female elephants also have tusks.

Theirs are smaller and not used for fighting in the same way as males.

But it's the details of the female's reproductive cycle that explains

the evolution of the male's bigger tusks.

Female elephants are pregnant for 22 months and, after they give birth,

they take care of their young for another two years.

A female will only be fertile for five days out of every four years.

That's an incredibly brief window of time.

It's less than one half of 1% of a female's lifetime.

So, that means, when you look across the landscape and you look at the

male and female elephants out there,

you're going to find that pretty much all of the bulls are ready

to breed at any point in time.

Every now and then, a female will become receptive and when she goes

into that window of fertility,

every male on the landscape enters into the fray.

Male elephants will travel for hundreds of miles

to find a fertile female.

Whenever there are more individuals of one sex able to breed than

the other, the result is going to be competition.

If you think of nearly any reproducing species,

you'll find that the females are invariably unable to breed

for long periods of time.

Female mammals become pregnant...

..they provide milk and care

for their offspring until independence...

..before reproducing again.

After laying their eggs,

female birds usually incubate and raise their chicks before they can

breed once more.

The same trend is repeated in many animals.

PUP WHIMPERS

Males are almost always ready to breed.

But reproductive females are rare and this sets the stage

for intense male rivalry.

In all of these animals where you

get these massive weapons, the males -

the bulls, the bucks - they face fierce competition.

And we think now that it's that second

critical ingredient for an arms race.

Competition is the second condition needed for animals

to evolve extreme weapons.

But must it always be the males?

Can competition ever cause females to evolve big weapons and fight?

30 years ago, behavioural ecologist Stephen Emlen discovered a key piece

of evidence to help answer this.

I haven't seen this in a long time!

He helped capture some remarkable film of an unusual tropical bird...

..the Jacana.

Sometimes these are called Jesus Christ birds because they

seemingly walk on water because their toes are so long,

they spread out their weight.

Male Jacanas are small. They incubate eggs in a nest

and raise the chicks.

Most females are bigger.

She'll defend large territories where many males may live.

Her only parental duty is to lay eggs in the male's nest.

So time-wise, the female, she is able to reproduce, in theory,

about every ten days. She could lay another clutch.

He's stuck for almost three months tending the eggs and the chicks.

So the tables are turned and that

means that females have to compete with each other

-for access to the males.

-Absolutely. Smart son!

HE LAUGHS

Stephen is Doug's father.

He pioneered studies, to show the effect of competition

on weapon development.

So, not only are the males doing the parental care,

but it means the females are fighting over access to the males.

And so the expectation is they

should have larger weapons than males.

These Jacanas have a single sharp yellow spur on each wing.

They're made of a tough, fingernail-like material

called keratin.

The female's spurs can be 25% larger than the male's.

And for good reason. They use their spurs in battles, to control access

to breeding males.

So, Jacanas actually teach us a lot about the evolution

of animal weapons.

They show us that, when the roles are reversed,

then the weapons are backwards, too.

Competition, in this case, is stronger in females.

They're the ones with the bigger weapons.

And in some Jacanas,

that role reversal has surprisingly cruel consequences.

If a male is left alone,

a new female will not hesitate to press her advantage.

Claiming the territory...

..the lone male...

..and obliterating the previous female's unhatched chicks.

And this is, sort of, a horrendous thing to think about.

Basically, she is now destroying his eggs.

-She wipes the slate clean.

-Exactly.

-So how much faster?

If he's on eggs like that one where she destroyed the eggs,

she's basically saved herself two months.

This brutal act means that the male is now available to breed and raise

the new female's chicks.

She gains a reproductive male.

With his eggs destroyed,

this male now has no choice but to mate with the female

who killed his offspring.

Jacanas may not have the biggest weapons...

..but they show that, even when the roles of the sexes are reversed,

if the conditions are right, an arms race can begin.

Many animals compete intensely to defend resources.

Like a territory, food or access to a mate.

They engage in free-for-all brawls.

Yet these species do not have extreme weapons.

So, something else, another condition,

must be needed to kick-start their evolution.

To find the answer, Doug turns to dung.

More specifically, the beetles that depend on it.

When you look at something like dung beetles,

they're literally competing for the same piles of dung.

And yet some of those beetles have these huge, spectacular weapons

and others have nothing at all.

There's two kinds of dung beetles.

There's the kind of dung beetle that carves the balls and rolls

them away. Class one, the ball rollers.

The ball rollers collect dung and move it to a safe place,

to raise their families.

Sometimes, there's a chaotic melee for control of a dung ball.

But these ball rollers don't battle with weapons.

They are unarmed.

Then, there's this other type of dung beetle that had been

less well studied. Those are what we call the tunnellers.

Significantly, the tunnellers have big horns.

They don't roll the dung.

Instead, they dig straight underneath it.

So, why have the tunnellers entered an arms race,

when their close cousins have not?

Doug set up a viewing system, to see what the tunnellers were doing

beneath the surface.

He had to use red lights, to avoid disrupting their natural behaviour.

The missing piece to the story was what happened underground.

Females dig tunnels beneath the piles of dung,

stashing it into these little brood balls, they're called,

and then she'd lay an egg very carefully at the end

of each one of these.

The males plant themselves at the entrance to one of these tunnels.

They've got hooks and spines on their legs that they can wedge into

the soil. They use their horns in fights with rival males.

They face out and any rival male that tries to get access to that

female's got to push past the guarding male.

And that's when fights break out.

Until Doug captured this rare, low-resolution footage 20 years ago,

nobody even knew these beetles fought.

The males use their shovel-like heads and sharp horns as weapons,

in brutal battles to control the female's brooding tunnels.

These beetles will walk right by each other on the surface and not

even bump each other. They couldn't care less.

But put them in a tunnel and, just like that, you've got a war.

Any rival males have to enter one at a time and they pretty much have

to face their opponent face-to-face.

The difference between the two types of dung beetle was that

the ball rollers fought in scrambles...

..whilst the tunnellers,

stuck in a confined space, were fighting in face-to-face battles.

They were duelling.

Doug wondered if one-on-one duels could be found in other species

with extreme weapons.

Chameleons have to be one of my favourite animals of all time.

They are the quintessential ambush predator.

They sit tight, they can change the colour of their skin,

their eyes can swivel in different directions,

so they move independently.

And, they have this fantastic ambush weapon,

so they can thwap out there with their tongue.

A chameleon's tongue is able to extend, like a telescope,

to twice the length of its body.

Wow! Look at that! Out of nowhere.

It can accelerate from zero to 60mph in one-hundredth of a second.

But there's another kind of weapon in, at least, some chameleons.

It's this other kind of weapon that I get excited about.

Even though all chameleons are closely related,

only a few have big horns on their faces.

There is a set of weapons.

These guys look like little dinosaurs.

Like a triceratops, with the horns coming forward from the head.

Male Jackson's chameleons use their horns to battle one another

on branches, over access to females.

Think of this like Jurassic Park jousting,

as these males push and pry and try to twist each other off the branch.

So, it turns out it's the details of the fight that matters.

If you look at this fight,

they're approaching each other face-to-face.

They're locking horns. They're pushing, they're straining.

Just like the tunnelling beetles, the chameleons are duelling.

It's no accident that, for 5,000 years of recorded human history,

the only sort of fight that has ever

mattered for honour or status was the duel.

Ritualised, repeatable and fair.

When males face off one-on-one in a duel, males with bigger weapons win.

So, this was that final ingredient.

The third - the missing - ingredient was duels.

Doug's discovery was the final piece of the evolutionary jigsaw.

Fights must be a face-to-face duel.

Only when animals fight in these ritualised duels do the benefits

of extreme weapons outweigh the costs.

What I'm suggesting is that, when these three conditions are met -

intense competition, defendable resources and duels -

selection for big weapons becomes so strong that it eclipses any costs

associated with these structures.

Nothing else matters.

Launching their populations onto trajectories

of explosive weapon evolution.

Most forms of life on Earth do not have extreme weapons.

The rare species that do come from a diverse range of different

animal families.

Doug's theory describes three simple conditions that unites them all.

A resource that's defendable...

..competition with a rival...

..and fights that take place as one-on-one duels.

And in the animal kingdom...

..when those three conditions are present...

extreme weapons can evolve.

But there are sometimes exceptions to rules.

The most iconic example...

..is an ancient, extinct beast.

We're looking at a fossil of a sabre-tooth cat.

This is the actual fossil.

It's not a cast. The animal probably lived in California

about a million years ago.

Sabre-tooths actually teach us an awful lot about animal weapons.

For one thing, you can't miss the teeth, right?

I mean, the teeth are huge.

But that's actually an interesting problem in itself,

because this is a predator.

The primary use for a sabre-tooth's colossal canines is thought to be

for hunting, not securing a mate.

This is why sabre-tooths are so exciting.

They're the exception.

It's the manner in which they caught their prey that explains why they

evolved extreme weapons.

Sabre-tooths are special because they're ambush predators.

Imagine what it would be like to get chomped on by something like that.

They sit and wait and then lunge out with a quick strike,

to grab unsuspecting prey.

For most predators, heavy armouries are simply too bulky.

They'd slow them down.

But, for ambush predators that strike quickly,

the evolution of big weaponry makes sense.

It works under the ocean, for things like mantis shrimp

and pistol shrimp.

It works for ant lions.

It works even for those crazy,

deep sea angler fish that are essentially a big jaw with a tail.

These guys had lures that they would dangle in front of them, that would

pull the prey into them.

Ambush predators use their extreme weapons

to capture and kill their prey.

But the majority of animals which have entered an arms race

aren't hunters.

All of the rest of the species with big weapons.

Species with the biggest and the craziest things sticking off

of their bodies, those animals are using

their weapons for reproduction.

These creatures use their weapons to fight each other.

You might imagine that their epic clashes

result in many lethal injuries.

But animals with extreme weapons use them in a manner that means,

win or lose, the likelihood is that you will survive the fight.

The very nature of a duel means that there are rules of engagement.

These species fight head-to-head, weapon-to-weapon,

which means they're less likely to be fatally gouged or gored to death.

For the ultimate test of this principle,

Doug is travelling to Washington State.

He's come to see the animal weapons record holder.

Hi. Can I see the biggest weapon in the animal world?

Sure.

-Here it is.

-That's it? It's not very big.

So, these are fiddler crabs. Ow!

Maybe it's a little bit bigger than I thought. So, this is it.

The record-holder.

So, it may be a small crab, but this claw, the weapon,

can be half of its body mass.

The claw can weigh as much as the whole rest of the crab.

It would be like you walking around carrying my whole body weight as one

-of your arms.

-That's incredible.

Fiddler crab claws are proportionately bigger than any

other known animal weapon on earth.

There's about 103 different species of fiddler crabs.

They live all over the world in the Tropics and they eat algae

off the surface of the mud.

Brook Swanson investigates the surprising advantages of these

super weapons at his fiddler crab lab.

So, females have two little claws.

They can actually eat twice as fast as the males.

The males only have these giant claws...

..and can't use their weapon claw to eat.

Right, he's bitten me three times already.

Can you show me what these guys can do?

Absolutely. We can use this force

meter to measure how strong their claws are.

This just measures how hard they squeeze.

Exactly. You put their claw right there.

-There you go.

-They squeeze.

That's about 20 Newtons.

So, the crab is producing about 20 Newtons with its claw.

5lbs of force.

So, like having a bag of sugar on a pin pushing on you.

So, it's not just 5lbs, it's 5lbs concentrated on a very sharp point.

-Exactly.

-That's why it hurts so much.

Crab claws have enough power

to slice straight through a rival's shell.

So, they're plenty strong enough to kill each other,

but when we keep them in the lab,

we hardly ever see them fighting and I've never seen one kill another one

in a lab. When you study these in the field,

it's very rare to see them fighting there, as well.

So, if they hardly ever use their giant claws to fight,

what do the male crabs use them for?

So, here we have two male fiddler crabs.

And their body size is about the same.

But, if you look at their claws...

-It's huge.

-..the claw's twice as big as the other one.

Wow, that is so obvious!

What they spend most of their time doing is not fighting with these

claws, but waving them in the air.

So, they walk around on the sand and they wave the claw

and wave the claw and wave the claw.

And they're signalling to the other crabs how big and how strong

they are.

And so, if you're looking at crabs by their claws,

you can easily tell the difference.

You can easily tell that this crab is bigger and stronger and a better

fighter. That's what makes the claw a good signal.

This is awesome. This is just like what we see in other animals.

You'd think the species with the really big weapons would use them

to fight all the time. And yet, what we see is the reverse.

That the species with the biggest weapons are actually

the most peaceful.

Paradoxically, it is uncommon for most animals

with extreme weapons to fight.

Although we revel in the rare moments these creatures do clash...

..in the natural world, confrontations seldom escalate into

head-to-head, brute force combat.

When rival males meet,

they will often avoid fighting, by measuring the prowess of their

opponent, using ritualised behaviours.

Elk males do this by strutting in parallel lines,

to assess the competition.

ELEPHANT BELLOWS

Nearly all these encounters end without a single blow being dealt.

So, we've gone from what was essentially a blunt-force weapon

to something that we now realise is a whole lot more than that.

The rival males are backing away, without even challenging them

in open battle.

These biggest weapons of all are acting as a deterrent,

settling dangerous contests without actual battle.

These fiddler crabs have a weapon so deadly that attacking

an equally-armed adversary could be suicidal.

In the animal kingdom,

the most powerful weapons are also the most effective deterrents.

So, I've been to some amazing places in my search for extreme

animal weapons. The place I'm going now is the strangest of all.

The weapons we're going to look at today

are both exciting and terrifying.

Doug has long wondered if what applies to the animal arms race

can be applied to our own.

Ross Millard is a captain at Malmstrom Air Force Base in Montana.

Can you tell me about the base?

Absolutely. We're here at Malmstrom Air Force Base.

We are one of three missile bases in Air Force Global Strike Command.

Our ultimate weapon here is the Minuteman-III nuclear missile.

-The big one?

-Yes.

The Minuteman-III is an intercontinental ballistic missile

that can be armed with a nuclear warhead.

These are the most destructive weapons on earth.

So, what can you tell me about the capability of these missiles?

The missile itself will take the warhead 7,000 miles and produce

a nuclear detonation.

Other than that, I can't get into

great detail on the power of the weapon...

-OK, fair enough.

-..the specific characteristics.

-But it's powerful?

-Yes. Not just powerful,

but designed and intended to work.

There are 150 of these missiles

ready to launch from bunkers in the 13,000 square miles

surrounding the base.

Captain Millard is taking Doug

to the missile launch training facility.

So, they are actually at different depths.

Some of them are a little more shallow,

just depending on the topography and the terrain.

Wow! I can't believe I'm in here.

From protected subterranean control centres,

missileers can fire the nuclear warheads.

All right. So, what does this console do?

Essentially, it allows

the crew members to be able to exercise command

over all the missiles that are assigned to them.

So, each control centre

is responsible for ten missiles, on this screen,

or on the far right-hand screen over there.

So, what would you say the primary function of these weapons is?

Day-to-day, the primary function is to provide a deterrence factor,

to let our adversaries know we have this capability.

But it's an interesting paradox for the system, because we don't want to

use it. But, if we have to use it, we have to know that it works

-as well, too.

-It's exactly the same in animals.

That do almost exactly the same thing.

You find the biggest, the craziest,

the most extreme animal weapons always work as deterrents, too.

If you're a male with the smaller weapons,

it often pays to assess the situation

and turn around and walk away.

All extreme weapons work as deterrents.

And the similarities do not end there.

One of the other parallels we see with animals is that when

the weapons get really, really big,

then only a few individuals in the population can afford them.

Realistically, how many countries could possibly afford to have

the infrastructure, the capabilities,

that we're talking about with a nuclear deterrence triad?

Very few. It's not that simple just because you have the missile.

There's all sorts of infrastructure.

There's the warhead, there's the support equipment,

there's all sorts of various increments along the way that add

to the complexity. The whole nuclear enterprise is much more expensive

than just one missile.

The costs associated with owning these weapons is phenomenal.

Of all the nations in the world,

only nine are thought to control nuclear warheads.

I just have to say again that that is exactly the same as what we see

in animals. It's exactly the same.

The reason the really big weapons work in animals is that they're so

unbelievably expensive that almost nobody can afford them.

That's part of why they work as a deterrent

is the best condition, the biggest bulls and bucks,

those are the only animals that can afford the really big weapons.

Captain Millard has agreed to show Doug a launch sequence.

So, we will launch the missiles, but the person who has the authority

is the President.

So, up in this container here, that one right there.

If you open it up, there's going to be a key in there,

as well as authenticators.

For Doug, there are parallels between the development of our own

super weapons and the evolution of the biggest weapons in nature.

So, manufactured weapons aren't parts of our bodies,

like tusks or horns.

Instructions for their construction aren't encoded in DNA.

But their form's changed through time, in much the same way

-as animal weapons.

-And go ahead and slide down.

When the conditions are just right,

manufactured weapons can get caught up in arms races, too.

Insert the launch key and, on my count, we'll turn and hold.

Surging forward to bigger and bigger sizes.

Deadlier, faster and vastly more expensive.

Three, two, one, turn.

Hold...and release.

If Doug's theory is right, all extreme weapons, human or animal,

evolve over time under the same conditions.

They cost an enormous amount of resources.

And their primary function is as a deterrent.

So, is there anything that can undermine the animals

with the most extreme weapons?

Doug was studying dung beetles,

when he discovered that the smaller males,

without the largest weapons, had found a sneaky way to reproduce.

So, one of the things that we were able to learn from these beetles

is that the little beetles cheat.

Doug already knew that males with big weapons guard the entrances

to female tunnels.

If you're another big beetle,

you can challenge him in outright open battle but, if you're tiny,

you don't stand a chance.

So, instead of fighting a losing battle,

they go right next to a tunnel and they start to dig their own tunnel.

They mine their way into the tunnel, come in beneath the guarding male,

go straight down to the female, find the female, mate with the female,

turn around and leave.

This small, sneaky male has found a way to evade the guard

and mate with the prized female.

Then he escapes up his own secret tunnel.

Big males have the weapons.

The big males fight the conventional battles.

The little guys break the rules.

The same cunning tactics can be seen in other species.

So, consider the cuttlefish.

In cuttlefish, you get all these little tiny males, these wimpy,

tiny runts. There's no way they would win, if they tried to fight

by the rules.

Big dominant males guard fertile females.

If an evenly-matched contender challenges him, occasionally,

they battle one another with sharp beaks and tentacles.

I would not want to get caught up in a tangle with one of these guys!

The winners hover above the females they want to mate with.

So, now we've got another cuttlefish coming up.

This one looks like a female...

..but it's not a female.

If you look closely, this is actually a tiny male...

..but he's cloaked himself in colours that make him

look like a female,

so he can come right up to the guarding male unmolested.

The sneaky male works his way right on in there and,

by looking and acting like a female,

he is able to get into a position

where he can breed with the female, too.

This female's eggs will be a mix of some massive macho male's

and some tiny trickster's.

These tactics are so pervasive

that Doug can even find cheats in Montana.

Jack Hogg is a bighorn sheep biologist.

He is taking Doug to search an island on Flathead Lake, to observe

their alternative tactics.

Bighorn sheep are famous for

engaging in epic, ritualised battles.

During the rut, rival males size each other up.

Occasionally, when it's an even match...

..they fight.

Through a series of horn-to-horn clashes,

the rams establish a hierarchy.

The winners become the dominant males.

During the breeding season, the victors guard fertile females.

Largest horned, largest bodied rams search for, and defend, ewes during

-their fertile period.

-So the biggest males with the biggest weapons,

their strategy is to guard access to the females for that one day

when they're fertile.

Jack's discovered that the subordinate males have their

own cunning mating strategy.

He calls it coursing.

The coursing strategy, in essence,

is to do whatever it takes to evade

the defence of a socially-dominant ram

who's defending a female during her fertile period,

but it's whatever needs to be done, whatever dirty trick,

to force a mating.

The dominant male here is called Crud Horn.

He's guarding a fertile female.

The fertile female has a white spot, so we're calling her White Neck.

A large group of subordinate males

are watching White Neck's every move.

They want to mate with her,

but Crud Horn is guarding her closely.

So Crud Horn has two important tasks in front of him.

One is to mate with her during her fertile period,

but he also has to defend the female against any male who wishes

to breed with her.

Typically, females run away from this group of large bodies that are

interacting. It's a dangerous place to be, so they run away,

and that's what creates the chase.

White Neck wants to escape the rush of coursing males.

Crud Horn is trying to keep up with her

and deflect the subordinate males during the chase.

Crud Horn's defence, actually, is extraordinary.

It's very good.

He's very physical, in terms of clashing and pushing and shoving

the other rams.

But, every once in a while, one of these coursers

will succeed in forcing a breeding.

One coursing male attempts to mate

with White Neck while she's separated

from Crud Horn in the scramble.

-That's all it takes, a few seconds?

-A few seconds.

The coursing male now could have a chance of fathering

White Neck's offspring.

By trying to mate with the female while running,

even for just a mere moment,

the coursing male has used

a tactic unrelated to the size of his weapons.

This is clever, in a way. It's almost like they are able to use

the bulk and the weight and the size

of the weapons of the alpha males against them...

..by getting them to lunge in a particular direction and then

taking advantage of being smaller and agile.

So, if all these males are using these alternative strategies,

is it even worth being the big alpha male?

-They do better.

-They still do better?

They have more babies, basically. A high-ranking male,

he would be the father of 60% of the lambs produced

by the females he defends.

The dominant male, the male with the biggest horns,

still fathers far more offspring

than all of the coursing males combined.

To the victor go the spoils.

We see this in every one of these animal systems,

that the biggest males are the ones

that can afford to produce the biggest weapons

and these males win, in every sense of the word.

Today, perhaps the biggest risk for many animals with extreme weapons

doesn't come from cheats.

It comes from a much more modern threat.

Weapon sizes in some populations of animals,

including bighorn sheep,

elephants and caribou,

are decreasing,

and the trigger for this change...

..is us.

Human trophy hunters prize the biggest tusks...

..horns and antlers.

Trophy hunting removes the genes for the biggest weapons.

In one elephant population,

the average tusk size was reduced by 40% in just 25 years.

And in another population,

the number of tuskless individuals increased by over 20%.

We have tipped the balance of these animal arms races.

Despite the human hunters...

..enormous biological costs...

..and being sabotaged by cheats...

..for animals in an arms race,

the males with the biggest and most extreme weapons

are the most successful.

These individuals are winning the evolutionary war.

They are not wiping themselves out.

And maybe that's a vital lesson for us.

ELEPHANT TRUMPETS

So this has been quite a journey for me -

a ride more wild than I ever could have imagined.

So, although most animal species don't have big weapons,

these extremes have arisen many different times independently

within separate lineages of animals.

What's the same, though,

are the conditions that are necessary in order to launch

that population into an arms race.

Who would have thought that the battles of beetles held lessons

for weapons everywhere?

Extreme weapons are extreme weapons.

Animal, human - it does not matter.

Their biology is exactly the same.

ELEPHANTS TRUMPET