Nova (1974–…): Season 44, Episode 26 - Extreme Animal Weapons - full transcript

Of the millions
of animal species on Earth,

only a few thousand are armed

with something strange
and special... huge weapons,

growing from their bodies.

Look at that set
of antlers, wow.

Antlers, horns, and tusks

wielded in titanic battles
against one another.

What gives rise
to these animal arms races?

- Wow, look at that.
- Out of nowhere.

How do some creatures develop
these massive weapons?

Why is it that this species
get sucked into an arms race



and ends up with
these huge weapons,

and this species,
which is otherwise

incredibly biologically similar,
does not?

What forces have driven animal
weapons to evolve

over millions of years?

Are some weapons just for show?

And can cheaters...

...ever win
at this evolutionary game?

What are the secrets

of "Extreme Animal Weapons"?

Right now on "NOVA."

Major funding for "NOVA"
is provided by the following:

In southwest Montana
is a hall of wonders.

Oh, my god.



Wow.

Unbelievable!

It's a temple of bone,

adorned with some
of the most impressive antlers

in the animal kingdom.

Look at this.

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

This is 20 pounds of bone

and they of course produce
two of them,

coming off the top of these
animals' heads every year.

Antlers are the fastest
growing bones described

from any living vertebrate.

Antlers are just one form
of animal weapon.

There are many others.

Horns.

Tusks.

Stings.

Nature's armory is diverse.

Weapons can be used in attack.

Or defense.

And sometimes their purpose
is a mystery.

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.

But sprinkled
through the tree of life,

there are species whose weapons
are taken to an extreme.

These have long fascinated
biologist Doug Emlen.

For me, I'm interested

in the weapons of offense,

weapons that are used
in fighting,

and, in particular,
the weapons that are big.

Why do some animals get drawn
into an evolutionary arms race,

with weapons getting
bigger and bigger?

While others do not?

Right on his doorstep
in Montana,

Doug can find
one of the best examples

of extreme animal weapons.

Look at that guy.

Rancher Doug Averill
keeps elk on his land.

They are tagged
so he can monitor them.

Here comes another one.

Male elk use their antlers
to control harems of females

and fight off rivals every fall.

The successful males get
the most mating opportunities

in the breeding season,
known as the rut.

They're all going to size
each other up here

when you get this
many bulls together.

This might get interesting.

Two bulls are approaching
one another.

This is pretty rare.

I haven't seen this all summer.

You can see they're
totally locked together.

Elk rarely fight to the death.

Because the male with smaller
antlers usually backs down.

In this case, the bigger bull
on the right has won.

The loser still wants a fight.

That's a temperament
to be an aggressive bull

down the road.

And he charges Doug.

That got my attention.

It's okay.

There is a downside to animal
weapons like elk antlers.

They require a huge
biological investment.

This is almost 20 pounds
of bone.

I mean 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 nother 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.

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.

Growing and maintaining a rack
of antlers each year

uses enormous amounts of energy.

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 damaged

and they've only got
a few short weeks

to make up the calories that
they've lost before winter

or they're not going to survive.

Elk need to stay strong.

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.

Considering what we know about
the costs of these weapons,

why would you ever want one?

These structures are not helping
the bulls survive.

Across the animal kingdom,

there's a high price
to being armed,

and these armaments
don't usually

help animals live longer.

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 a multitude
of weird and wonderful traits

that make them attractive
to the opposite sex.

The same evolutionary pressure

that produces
these characteristics

is also behind
many extreme weapons.

It's known as sexual selection.

And elk bulls
are a prime example.

Bigger antlers help them
win more battles

and mate with more females.

So the genes for the largest
weapons are passed

to the next generation.

Research has shown
that the biggest bulls

sire the most offspring
over 80 percent of the time.

This happens throughout
the animal kingdom.

Doug observed it
while studying a creature

much smaller than elk.

But one that still wields
an impressive armory.

So this is an example

of a Japanese rhinoceros beetle.

And 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.

They can be 30 percent
of their body weight.

That is literally like you or me
wearing a coffee table

around on the tops of our heads.

There are hundreds of thousands
of different beetle species.

But only a small fraction
carry extreme weapons.

Why do these few enter
into an arms race?

So there's an animal

with an incredible weapon.

The male Darwin's beetle
from Chile

has an enormous set
of pincers for its size.

These specially adapted jaws can
make up half their body length.

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,

and the pincers on these males
can be even longer

than the rest of the body
of the animal.

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.

But what's the point of this
epic battle?

Beetles like this
fight over wounds,

sort of marks or nicks
on the sides of a tree

where sap will ooze out
and drip down the side.

Females feed on that sap.

By guarding the sap, a male
beetle gains access to females.

So that means that
if you're a male,

and you can hold onto
that real estate,

you have opportunities
to mate with the females

when they come in to feed.

Darwin's beetles
use their weapons

to keep other males away.

But not all conflicts are tied

to such a specific place
or food source,

and those battles have
a different set of requirements.

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.

They'll get into these
big, frenzied,

acrobatic, mid-air snarls.

In 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.

But male Darwin's beetles
do have a specific resource

to defend.

The males that are able to win
these battles

or to hold onto
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 did these particular species
have such incredible weapons?

The first clue,
the first piece to the puzzle

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

Most animals
with extreme weapons

are keeping females away
from male rivals.

Male hippos use their
enormous teeth to do this.

Male white rhinos
try to defend territories

that females travel through.

And male elephants
use their tusks in combat

to keep fertile females
away from adversaries.

Each of those tusks can
be like 100 pounds of ivory.

These are huge teeth.

Ah, his tusk shattered.

Okay, there you go.

That is the impact
we're talking about here:

it shattered the tusk!

But across the animal kingdom,

why do the largest weapons
almost always belong

to the males?

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,

but theirs are smaller
and not used for fighting

like the males'.

Unlike the males,
females spend most of their time

caring for offspring.

Pregnancy lasts for 22 months
and after females 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 one
percent of a female's lifetime.

So fertile females
are extremely rare.

Every now and then,
a female will become receptive

and when she goes into
that window of fertility,

every male in the landscape
enters into the fray.

It's common throughout
the natural world

that females are often
unavailable to breed

for long periods of time.

After giving birth,
most female mammals provide milk

and care for their offspring

until they can survive
on their own.

Only then can the mothers
reproduce again.

After laying their eggs,
female birds usually incubate

and raise their chicks
before they can breed once more.

Reptiles, fish, insects.

The same trend is repeated
in many classes of animals.

Males are almost always
ready to breed.

But reproductive females
are rare.

And this imbalance
sets the stage

for huge competition
among males.

Competition is
absolutely critical.

In a sense, it's the fuel
that drives the arms race.

In all of these animals where
you get these massive weapons...

The males, the bulls,
the bucks...

Face fierce competition
over access to females.

While males are usually
the ones that compete,

occasionally,
the roles can be reversed.

Thirty years ago behavioral
ecologist Stephen Emlen,

Doug's father, helped capture
some remarkable footage

to illustrate this.

Man, I haven't seen this
in a long time.

The film features the unusual
tropical bird

that Stephen studies,
called the jacana.

We conducted all this study

basically in Panama.

Sometimes these are called
Jesus Christ birds

because they seemingly
walk on water

because their toes are so long
they spread out their weight.

The smaller male jacanas
incubate the eggs

and raise the chicks

while the bigger females
patrol large territories

where males are usually found.

So time-wise the female,

she's 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.

Stephen Emlen is an expert
in animal breeding behavior.

So, not only are the males doing

the parental care but it means

the females are fighting

over access to the males
and the care they provide,

and so the expectation
is they should have

larger weapons than males.

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

They are made of
a tough fingernail-like material

called keratin.

The spurs of the females can be

25 percent larger
than the males.

They use their spurs in battles

to control access
to breeding males.

So jacanas actually teach us
a lot about the evolution

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 the winner presses
her advantage.

Claiming the territory,

the lone male, and obliterating

the previous female's
as-yet-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 just destroyed
the eggs,

she's basically saved herself
two months.

She gains a reproductive male.

Instead of spending
the next two months

taking care of
his eggs and chicks,

the male is now available,

and mates with the female
who killed his offspring.

With their small
but sharp weapons,

female jacanas
show how competition

is a powerful
evolutionary force,

even when the roles
of the sexes are reversed.

But is it
the only force at work?

Many animals compete intensely
for territory, food, or a mate.

Their fights can be vicious.

But most of these species
don't have giant weapons.

Doug began to study
dung beetles,

looking for what else might be
needed for extreme weapons

to evolve.

When you look at something
like the dung beetles.

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

And yet some of those beetles
have these huge,

I mean spectacular weapons
and others have nothing at all.

There's two kinds
of dung beetles.

There's a kind of dung beetle
that carves the balls

and rolls them away...

Class one, the ball-rollers.

The ball-rollers are unarmed.

They collect dung and move it
to a safe place

to raise their families.

Sometimes they have
free-for-all brawls

for control of a dung ball.

But they don't have
large weapons.

But then there's this other type
of dung beetle

that had been less well studied,

and those are what we call
the tunnellers.

The tunnellers have big horns.

They don't move the dung.

They dig straight underneath it.

By comparing
the two types of beetle,

Doug believes he can find
the crucial factor

that launches an arms race.

He set up a viewing system

to see what the tunnellers
were doing below the surface.

He had to use red lights
to avoid disrupting

their natural behavior.

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.

What you find is that the males

plant themselves at the entrance
to one of these tunnels,

they brace themselves there.

They've got hooks and spines
on their legs

that they can wedge
into the soil,

and they use their horns
in fights with rival males.

Until Doug captured this unique
scientific footage 20 years ago,

nobody even knew
these beetles fought.

Doug revealed that males use

their shovel-like heads
and sharp horns

as weapons.

Rivals engage
in brutal underground battles

to control the females'
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 you 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 have to face
their opponent face to face.

The difference between the
tunnellers and the ball-rollers

is that the ball-rollers fight
in group scrambles,

while the tunnellers,
stuck in a confined space,

engage in one-on-one battles.

And these are the beetles
with the weapons.

Doug wondered
if this kind of fight

could be found in other types
of animals.

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

They are the quintessential
ambush predator.

So they sit tight,

their eyes can swivel
in different directions

so they move independently.

Thwap.

A chameleon's tongue is able to extend
to twice the length of its body.

Wow.

Look at that, out of nowhere.

It accelerates from zero
to 60 miles per hour

in one-hundredth of a second.

But another type of chameleon

has an additional
set of weapons:

big horns on their faces.

So 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 fight one another
over access to females.

Think of this
like "Jurassic Park" jousting,

as these males push and pry

and try to twist each other
off of the branch.

The branch itself is the key.

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.

It almost looks like
they're dueling.

When males face off
one on one in a duel,

males with bigger weapons win.

Chameleons use their horns to
help win face-to-face battles.

So for me, the... the penny
dropping, the moment,

the epiphany when everything
clicked and came together

was that the nature
of the fight mattered,

and, in particular, duels
were the crucial ingredient

that could spark an arms race.

So competition is not enough
to set the stage

for extreme weapons.

The battles almost always
include

ritualized head-to-head combat.

When this happens,
the evolution of extreme weapons

seems to outweigh the costs.

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.

Extreme weapons have evolved
many times over

in the history of life...

...the rare species

that possess them

coming from a diverse range
of animal families.

So in each of these cases,

the conditions
had to be just right

in order for the populations

to launch on
to this type of a trajectory,

leading to these bigger and
bigger and bigger weapon sizes.

This evolutionary mechanism
dates back

hundreds of millions of years.

Fossils bearing
extreme weapons...

...have been found
around the globe.

Doug heads to Salt Lake City

to examine the
fossilized remains

of a famous dinosaur family.

Mark Loewen studies
a group of dinosaurs

called the ceratopsids.

Welcome to the horned dinosaurs.

They're amazing.

We have triceratops, the iconic horned dinosaur.
I recognize that one.

So these lived
during the Cretaceous,

between 80 million years ago
and 66 million years ago,

when most of the dinosaurs
went extinct.

Here we have
a mega herbivorous animal.

This is, like, the rhino of
the Cretaceous, or the elephant.

Scientists estimate
that some ceratopsids

could weigh seven tons.

They were probably preyed on
by Tyrannosaurus rex.

But did the ceratopsid dinosaurs
use their horns

in fights with each other

like male animals with weapons
do today?

In this collection, there are
hundreds of different specimens

of ceratopsid dinosaurs.

Right here, we have actually
the oldest

of the ceratopsid dinosaurs.

This is diabloceratops,

a really cool animal,
80 million years old.

If we look in places
where the horns would hit

when these two animals
locked together,

here we have a hole.

This is a puncture wound
into this bone

that's been rehealed
during its life.

Mark thinks that holes like
these are puncture wounds

from violent face-offs
with other ceratopsids.

So this is totally consistent
with head-locking behavior

and being punctured by the horn
of another adult animal.

That's just like
what other animals do.

Yeah.

And this is something we can
show quite conclusively

in triceratops.

These scarred fossils suggest
that horned dinosaurs

were using their weapons
in face-to-face contests,

just like animals
with extreme weapons do today.

And like today's
elephants and elk,

these dinosaurs were herbivores.

Their giant weapons were used
in battles for dominance,

not for dinner.

It turns out that predators,

from Tyrannosaurus rex
to today's wolves and lions,

don't usually wield
extreme weapons.

Their teeth and claws
are relatively small.

But there are exceptions.

The most iconic example is
another ancient extinct beast.

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

And this is the actual fossil...
It's not a cast...

And the animal
probably lived in California

about a million years ago.

Saber-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,

because this is a predator.

This is why saber-tooths
are so exciting.

They're the exception
in this case.

While the enormous fangs may
have helped attract females,

their main use seems to have
been to hunt for prey.

Saber-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 armories
are simply too bulky.

They'd slow them down.

But for ambush predators
that strike quickly...

...the evolution of big weaponry
makes sense.

And that logic works
under the ocean

for things like mantis shrimps
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 most animals that are
in 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.

So is mortality
among these heavily armed males

exceptionally high?

How do they
avoid lethal injuries

when using
their extreme weapons?

A clue may come
from a tiny animal

with the largest known weapon
proportionate to body size.

All right, Brook,
can I see the biggest weapon

in the animal world?

Sure.

Here it is.

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

So these are fiddler crabs.

Ow! Okay, that was...

Maybe it's a little bit
bigger than I thought.

So this is it, the recordholder.

So it may be a small crab,

but this claw, the weapon,

can be half of its body mass,

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

It'd be like you walking around,

carrying my whole bodyweight
as one of your arms.

That's incredible.

Fiddler crab claws

are proportionally 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 studies
the costs and benefits

of this surprisingly large claw.

So females have
two little claws,

and 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.

The huge claw comes
at a great cost.

Males must eat extra food
to fuel their muscles,

but they are only able
to gather it

half as fast as the females.

All right, so he's bitten me
three times already.

Can you show me
what these guys can do?

We can use this force meter

to measure how strong
their claws are.

This just measures
how hard they squeeze?

Exactly.

Put their claw right there.

They squeeze.

That's about 20 newtons.

So the crab is producing

about 20 newtons with its claw.

Five pounds of force,

so like having a bag of sugar
on a pin pushing on you.

So it's not just five pounds;

it's five pounds concentrated

on a very sharp point.
Exactly.

That's why it hurt so much.

So is this strong enough
to pierce another crab's shell?

A machine in the lab
can measure that

using the shell of a dead crab.

That could take

about five newtons of force.

Five newtons.

So way less than
the squeezing force.

The big claw's pinching strength
is four times more

than what is needed
to pierce another crab's shell.

So this is technically
a lethal weapon.

Exactly.

Crab claws are powerful enough
to kill a rival.

But there's a paradox.

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 the lab,

and when you study these
in the field,

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

Male fiddler crabs sometimes
duel with their weapons

on the beach.

But they spend much more time
using their giant claws

in another way.

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 they're signaling
to the other crabs

how big and how strong they are.

So what makes the claw
a good signal

is that it's hypervariable.

There's a lot of variation
between crabs,

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,

and that's what makes the claw
a good signal.

This is awesome.

You'd think that 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.

It turns out that what's true
for fiddler crabs

is also true for a variety
of animals with extreme weapons.

Display and ritual are often
more important

than brute-force combat.

When rival male elk meet,

they measure the prowess
of their opponent

with ritualized behaviors.

They do this by strutting
in parallel lines

to assess the competition.

Most of these encounters
end with one animal backing off

without a single blow.

The fiddler crab's deadly claw
is the ultimate example

of a weaponized deterrent.

So we've gone
from what was essentially

a blunt-force weapon

to something that we now realize

is a whole lot more than that,
right?

These biggest weapons of all
are acting as a signal.

They're behaving
like a deterrent,

settling dangerous contests
without actual battle.

And the destructive claw still
has another important purpose.

It's not just the other males
that are seeing

this giant signal,
this huge claw,

but it's the females, too.

The females will walk
through groups of males

that are waving
their giant claws

and she'll make a choice.

So she'll choose the males
with the largest claws

or the males
that wave the claws the best,

and so it's not good enough
for a male to be able

to just win fights.

He also has to be able
to attract a female

and he does that with his claw.

So these are
the ultimate signals.

Both males and females
are paying attention.

I know what she would choose.

But what about individuals
with less impressive weapons?

Is there any chance for them
to find a mate?

Doug uncovered
some sneaky tactics

while he was studying
dung beetles.

So one of the things
that we were able

to learn from these beetles

is that the little beetles
cheat.

Female dung beetles dig burrows

and big males
guard the entrances.

This female is dragging dung
down to her nest

before she lays her eggs.

You've got this main tunnel.

You've got the big beetle
guarding that tunnel.

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,

coming 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 can escape
up his own secret tunnel.

Big males have the weapons;

the big males fight
the conventional battles.

The little guys break the rules.

And that means
that the biggest animal

with the largest weapon

doesn't always win.

So consider the cuttlefish.

In cuttlefish, you've got all
these little tiny males.

I mean, these wimpy tiny runts
in these populations.

There's no way they would win

if they tried to fight
by the rules,

so they don't.

Big dominant males guard
fertile females.

If an evenly matched contender
challenges him,

sometimes they will 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,

often smaller
with paler coloration.

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 colors

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's able to get into a position

where he can breed
with the female, too.

When this female lays her eggs,
her offspring will be a mix

of some macho males
and some tiny tricksters.

These strategies appear
in a variety of species.

Back in Montana, bighorn sheep
biologist Jack Hogg

is taking Doug to an island
on Flathead Lake

to search for another
underdog tactic.

Bighorn sheep
are famous for engaging

in epic ritualized 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

with the dominant males
at the top.

During breeding season,

they will guard fertile females.

The 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.

In order to mate,
the subordinate males

have their own cunning strategy.

Jack calls it coursing.

The coursing strategy in essence
is to do whatever it takes

to evade the defense
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, you know, interacting.

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

and that's what creates
the chase.

White Neck attempts 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 defense 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 by the melee.

That's all it takes
is a few seconds.

A few seconds.

He now has a chance of fathering
White Neck's offspring.

In this case,
the smaller size of his weapons

may have had some advantage.

The coursing ram has succeeded

in breeding the female.

He has a ticket in the lottery.

He has a chance
of fathering the lamb

that she produces next spring.

It's clever in a way.

It's almost like they're 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

by zipping around them and
getting access to the female.

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 percent
of the lambs produced

by the females he defends.

White Neck's offspring is far
more likely to be fathered

by Crud Horn, the dominant male
with the biggest horns,

than all his rivals 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.

In nearly every species
with weapons,

cheating is the best strategy
for the underdogs,

but bigger weapons still provide
the best opportunities

for males to produce
more offspring.

Yet the balance of the animal
arms race may be tipping.

Weapon sizes
in some populations,

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.

But animals shot down
can't have offspring.

Trophy hunting removes the genes
for the biggest weapons.

In one elephant population,
the average tusk size

was reduced by 40 percent
in just 25 years.

And in another, the number
of tuskless individuals

increased by over 20 percent,

threatening an evolutionary
trend that has existed

for millions of years.

So this has been quite
a journey for me,

a ride more wild
than I ever could've imagined.

Who'd have thought that the
battles of beetles held lessons

for weapons everywhere?

Whether in beetles
or fiddler crabs,

elk or elephants,

extreme weapons have arisen
independently

many different times.

Despite the enormous cost,
in the right conditions,

head-to-head combat
with extreme weapons

is still the best strategy
evolution offers

to help pass genes
to the next generation.