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Monkeys and apes are our closest relatives.

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They have the richest social life
of all mammals,

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and much time is spent
establishing relationships

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and climbing the social ladder.

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And that has had
some remarkable consequences.

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South America.

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A few capuchin monkeys
are having a morning get-together.

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Capuchins are like the earliest monkeys,
judging from fossils -

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the basic pattern, you might say.

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Their grasping hands and gripping tails

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enable them to race through the forest
with astonishing speed and agility.

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But it's their big brains
that really give them an edge.

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One thing that's characteristic of monkeys

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is their ability to spot an opportunity
and then exploit it.

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Of none is that more so than these capuchins.

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They'll always grab a ripe fruit,

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but they investigate everything.
Little escapes them.

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Their inquisitiveness really impresses you
when you follow them.

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They look for food everywhere.

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Their colour vision is excellent, but their
sense of smell is no better than ours.

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So to find food that's hidden from view,
they use not their noses, but their brains.

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They can imagine what might
be lurking beneath dry leaves.

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Out of sight, for them, is not out of mind.

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A good memory must help.

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Recalling a previous experience
makes the difference between getting stung

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and getting honey.

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The troop is just entering these mangroves.

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Most mammals wouldn't find much to eat here,

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but the monkey's big brain
enables them to find things others miss.

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Only the bolder ones
chance their hand with crabs.

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It's brave to tackle claws with delicate fingers.

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The retreating tide also exposes shellfish,
but eating those poses problems.

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The clams are certainly full of meat,
but it's locked behind closed doors.

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However, grasping hands, guided by a big brain,
can deal with that problem.

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These clams are very tough.
I'd have difficulty in opening them myself.

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But these monkeys have learned
that if you hit them long enough,

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the clam relaxes, the shells can be opened,
and they can get the meat inside.

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The whole troop know the trick. Over 20
of them are giving the clams the treatment.

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Ten minutes on, and the clam shells
are still tightly clenched.

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This is hardly fast food.

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The young watch attentively.
Most will learn how to do it,

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so the technique will be passed
to the next generation.

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But it takes years for a young monkey
to get it right.

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Patience is important.
Unfortunately, so is technique.

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Capuchins, like us,
have varied personalities and abilities.

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Some never get to grips with clam cracking.

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Those with a good technique and perseverance
are now collecting their rewards.

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Some aren't exactly thrilled by what they find.

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It's not just food
that monkeys collect from the forest.

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These two bunches of leaves
look much the same,

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but this kind is used by the local people
as an antiseptic and an insect repellent,

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whereas this one
has no medicinal qualities at all.

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If I put them both down, I think I know
which the monkeys will choose.

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Those are pipa leaves -
the ones with insect-repelling sap.

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Pipa is usually hard to find,
so this bunch will cause excitement.

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Pipa rubbing is a major social event.

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Those taking part disregard their
differences and everyone joins in the party.

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Do the capuchins know that this protects them

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against skin infections and mosquitoes?
It's impossible to say.

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But it is the case that they do it more
frequently during the rainy season -

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when there are more mosquitoes around -
than at any other time during the year.

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Not all capuchins use pipa,

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but once an individual discovers it,
the knowledge spreads,

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so pipa leaf rubbing becomes a group tradition.

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Capuchins eat most things.
Some monkeys, however, have specialities.

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These are uakaris,
and they will eat fruit of an unusual kind.

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Their face colour indicates their social position.

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The brighter the scarlet,
the more senior the animal.

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Such excellent colour vision
also helps them to select their fruit.

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Unusually, sakis are able to eat fruits
that are vivid green and not ripe.

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The monkeys here can all eat different foods,

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allowing many species to live side by side.

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The saki has special teeth to eat nuts
that no other monkey can crack.

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The spider monkey has long limbs
and a grasping tail,

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which enable it to collect the very ripest fruit.

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But there are foods in this forest
that not even a spider monkey can get to.

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There's food for monkeys
in every part of the rainforest,

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but some of it is difficult to reach.

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I've got up into the canopy in a crane,
and I'm 120 feet above the ground.

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Here on the outermost twigs,

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the stems are so thin, they couldn't support
a normal-sized monkey.

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Yet there's a lot of food up here.

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Underneath these leaves, a cocoon,
a caterpillar, another leaf-eating insect.

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But there is one kind of monkey
that can get up here and catch these.

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It's a pygmy marmoset.

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The smallest monkey in the world -
no bigger than my hand.

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Its feet are too small to grasp anything
but the thinnest twigs.

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Their sharp claws prevent them from slipping.

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As it stalks its insects,

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it has to move with great stealth
lest any vibration should scare them off.

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But these hunters are so small
that not even the thinnest branches tremble.

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Monkeys have forward-pointing eyes
with which to judge distance -

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invaluable when moving around in the trees -

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but this tiny hunter
uses that ability also to pounce.

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But their staple diet is more extraordinary.

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You might think these lumps
are a natural feature,

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but in fact they're wounds,
inflicted by pygmy marmosets

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that come to this tree trunk every day.

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It's eating gum which it's forced the tree
to produce by gnawing its bark.

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It's also making sure
that there's going to be gum tomorrow

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because it's also reopening the wounds
that the tree has healed up.

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The marmoset opens these wounds,
the tree closes them,

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until so much scar tissue builds up
that mounds appear.

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Generations of pygmy marmosets
have done that on this particular tree,

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resulting in these huge columns
of lumps running right up the trunk.

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A well-managed gum tree
is a huge asset to a group of marmosets

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and that makes it
a tempting target for thieves...

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..and a rival group is preparing to invade.

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The intruders charge and the owners flee,
leaving their precious gum undefended.

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As the invaders steal the gum,
the displaced residents start scent marking.

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This seems to reinforce
the bonds between them,

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and they launch a counterattack.

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(SCREECHING)

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It works.
The home team are back on their tree.

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You can share a food resource
that's cropped by others

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without a face-to-face confrontation.

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You might think that at sundown
all monkeys are preparing to sleep.

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That's almost true, but not quite.

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Only one monkey in the world
collects its food by night.

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And precisely because it's nocturnal,
it's seldom seen and still little known.

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There's a family of them living
in this tree. They're dourocoulis.

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They're also known,
for obvious reasons, as owl monkeys.

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Their eyes may be huge
but their night vision is not that good,

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which suggests
that their ancestors lived by day

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and that dourocoulis became nocturnal
comparatively recently.

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During the day, the flowers on which
they feed are guarded by other monkeys.

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By coming out only at night,
dourocoulis avoid having to fight for a share

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and can feed in peace.

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Day breaks.

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The dourocoulis retire and other
fruit and nectar-feeding monkeys awake.

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Tamarinds set off to collect their share.

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The forest is not rich in such food,
and although tamarinds live in small groups,

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finding all they need takes time.

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The female always produces twins,
which travel with the family.

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She has two male partners.

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Using her tongue, she signals
that it's time one took over the twins.

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Both are eager to do so.

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Both mated with her,
so each has cause to regard the babies as his.

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But the twins have other ideas.
They want to stay with Mum.

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She gets rid of them at last,
and it's important that she does.

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She provides them with milk,
so she must eat more than usual

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and she would find that difficult
if always burdened by her babies.

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The situation is made harder because
there are other kinds of tamarinds here.

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This is one of them -
a saddleback tamarind.

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Monkeys usually guard food ferociously,

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but these tamarinds often feed side by side.

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And when one leaves, the other follows.

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The emperors go first and the saddlebacks
with their shorter legs try hard to keep up.

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The travelling party shares a quick refuel.

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Both kinds of tamarind, being small
and energetic, need frequent snacks.

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They share another thing - an enemy.

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They give alarm calls to both species.

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A tayra - a kind of giant weasel.

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Not the most dangerous predator
in this forest, but deadly to a small monkey.

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It's certainly safer to travel in groups,

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but sharing food is a high price
to pay for a warning system.

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There is, however,
another more subtle advantage.

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Each flower needs time
to refill its reservoir of nectar

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after a visitor has drunk from it.

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If either tamarind followed separately,
they might make a long journey

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only to reach a tree
that had been emptied by the other.

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That would be disastrous for an animal
that has to feed so regularly.

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It's better for tamarinds to travel together
and then share the food when they arrive.

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Howler monkeys -
ten times the size of a tamarind.

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They also eat flowers,
but these are not always available.

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In tropical forest, at least leaves
can be found all year round,

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and howler monkeys specialise on these.

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The best leaves are in the canopy,

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so that's the best place to go to watch howlers.

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Leaves are not all the same. Some are
poisonous even to a howler monkey

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and some edible ones are nicer than others.

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Once again, that monkey ability
to see in colour is a great help.

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These red ones are young and succulent
and would be very good to eat

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if they weren't protected by poisons.

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These mature ones are green
and the poison in them has faded,

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but they're fibrous and not very good to eat.

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A leaf-eater wants
something in between - like this.

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Imagine how difficult
it would be to pick the right one

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if you didn't have colour vision.

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Even the best leaves are not easy to digest,

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so howlers spend a short time
collecting their food,

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but a long time digesting it.

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In fact, they spend half of every day
just lying around, like cows chewing the cud.

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Even after all that digestion,
leaves are not very nutritious.

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Howlers can't afford
to waste energy chasing away rivals.

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They use a more labour-saving way.

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(LOW WHISTLING)

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(CACOPHONY OF HOWLING)

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Howlers have a specially-enlarged bone
in the throat - a hyoid -

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that enables them to make
this extraordinary song.

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It's one of the loudest noises
made by any animal.

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The whole family joins in
almost every evening.

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They can work themselves up
into quite a frenzy.

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But since neither they nor their rivals move
anywhere, it's hard to say who's winning.

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It may be that howling serves to strengthen
family solidarity and deter intruders.

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(FAINT HOWLING)

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(CROAKING CALL)

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That may sound like a howler monkey,
but I've now left South America, I'm in Africa.

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That's the howler's African equivalent -
the black and white colobus.

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As in South America, many different kinds
of monkeys share the same forest,

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because they find their food
in slightly different ways.

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Red colobus have a special stomach
and can eat unripe fruit and leaves.

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00:25:01,407 --> 00:25:04,444
Sooty mangabeys, like saki monkeys,

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have extremely powerful jaws
that can break open tough foods.

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The other monkeys
are more general in their diet.

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and they belong to a group called the guenons.

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All guenons eat fruit and insects,
but each feeds at its own level in the forest.

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There are 17 different kinds of guenon in Africa.

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They all have similar shape bodies,

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but each has its own colours
and patterns that serve as social signals -

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allowing them to recognise
friends and rivals at a glance.

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They're the most colourful
group of monkeys in the world.

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Colour signals are not
a good way of sending messages

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in places where the visibility is poor,

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and that's certainly the case
here in the Tai forests in West Africa.

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If you miss a warning of danger,
the consequences could be fatal.

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How do monkeys keep out of harm's way?

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I'm with one of the most extraordinary
anti-predator alliances in the world.

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Around me is a troop
of sooty mangabeys and mongooses.

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They are keeping an eye out
for danger on the ground.

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00:26:47,887 --> 00:26:53,280
Above me, there are at least
five or six other species of monkey

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ready to detect a threat from the sky
or from within the canopy.

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In this alliance,
monkeys of many kinds travel side by side.

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It's a huge safety network
that extends from the canopy

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right down to the forest floor.

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With so many pairs of eyes at every level,
someone is almost certain to spot a threat,

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no matter where it comes from.

228
00:27:27,967 --> 00:27:35,203
There's little squabbling over food between
species as each finds it in a different way.

229
00:27:38,727 --> 00:27:44,165
Visibility is so poor that the monkeys
communicate almost entirely by sound.

230
00:27:44,327 --> 00:27:48,605
A sound reaches every monkey
in a split second.

231
00:27:48,767 --> 00:27:53,557
It's the best means of staying in contact
or warning of danger.

232
00:27:55,007 --> 00:27:57,885
Diana monkeys forage high up the canopy,

233
00:27:58,047 --> 00:28:02,598
so they're usually first
to spot danger from the air.

234
00:28:06,847 --> 00:28:09,645
Crowned eagles are never far away.

235
00:28:09,807 --> 00:28:13,641
If one comes too close,
a specific alarm will be sounded

236
00:28:13,807 --> 00:28:17,038
telling monkeys to drop for cover.

237
00:28:27,847 --> 00:28:32,363
Danger above! Monkeys plummet down
without looking up.

238
00:28:35,567 --> 00:28:39,162
The alliance has saved another member.

239
00:28:40,207 --> 00:28:46,476
All these monkeys have different alarm calls
for different predators. Watch this.

240
00:29:12,407 --> 00:29:15,797
(SHRILL CALLS)

241
00:29:18,927 --> 00:29:22,203
(CROAKING CALLS)

242
00:29:25,367 --> 00:29:27,403
(ECHOING BARK)

243
00:29:27,567 --> 00:29:31,276
That's the leopard alarm call
of the Diana monkey.

244
00:29:32,687 --> 00:29:35,963
That totally different one is the spot-nose.

245
00:29:36,127 --> 00:29:42,362
The point is that all species of monkey
in the alliance recognise one another's call

246
00:29:42,527 --> 00:29:45,325
and know the nature of the enemy.

247
00:29:45,487 --> 00:29:51,323
That's important because each predator
requires its own particular response.

248
00:29:53,927 --> 00:29:58,398
All these monkeys now know
that there's a leopard around,

249
00:29:58,567 --> 00:30:04,119
so you might think they'd flee. But they don't.
They're advancing towards it.

250
00:30:04,287 --> 00:30:08,041
That's because the leopard
is an ambush predator.

251
00:30:08,207 --> 00:30:12,280
Once it's been spotted, it usually gives up.

252
00:30:13,247 --> 00:30:15,681
Monkeys are drawn by the call.

253
00:30:15,847 --> 00:30:21,877
They even drop lower and closer
so they can keep the cat in full view.

254
00:30:24,447 --> 00:30:29,567
And here they will stay on maximum alert
until the leopard gives up

255
00:30:29,727 --> 00:30:32,605
and leaves them in peace.

256
00:30:45,407 --> 00:30:49,116
The ancient city of Polonnarwua in Sri Lanka.

257
00:30:49,287 --> 00:30:54,805
The civilisation that built it
a thousand years ago has long since crumbled.

258
00:30:54,967 --> 00:31:01,236
But one society that lived here then
is still here now, and thriving.

259
00:31:04,967 --> 00:31:08,755
Toque macaques
have walked these walls for centuries,

260
00:31:08,927 --> 00:31:15,366
but only in recent decades have we started
to understand their complex society.

261
00:31:24,767 --> 00:31:28,760
This is one of the most studied
monkey groups of all time.

262
00:31:28,927 --> 00:31:34,320
For the past 30 years, their trials
and tribulations have been recorded,

263
00:31:34,487 --> 00:31:38,765
and that has given us
remarkable insight into their lives.

264
00:31:40,767 --> 00:31:46,239
These youngsters are playing as equals,
but they have different futures ahead.

265
00:31:46,407 --> 00:31:49,877
There's a ruthless class system
in monkey society.

266
00:31:50,047 --> 00:31:55,724
Those born into high-ranking families
have a massive head start in life.

267
00:31:57,887 --> 00:32:01,800
Imelda is one of them. She is high born.

268
00:32:01,967 --> 00:32:06,677
Others have been feasting on berries,
but she's arrived too late -

269
00:32:06,847 --> 00:32:11,045
all the berries
are in the cheek pouches of others.

270
00:32:12,087 --> 00:32:18,879
Imelda spots Poppin. She's larger and older,
but she's from a lower-ranking family,

271
00:32:19,047 --> 00:32:24,280
and that entitles Imelda
to take anything of Poppin's that she wants,

272
00:32:24,447 --> 00:32:27,757
including the food right out of her mouth.

273
00:32:34,487 --> 00:32:37,684
Poppin makes it as hard for her as she dare,

274
00:32:37,847 --> 00:32:44,036
but if she resists too strongly, she risks
a beating from the rest of the troop.

275
00:32:55,687 --> 00:33:01,603
In monkey society, it helps to be high born,
but it also helps to be intelligent,

276
00:33:01,767 --> 00:33:07,683
and that is particularly apparent
during the mating season.

277
00:33:07,847 --> 00:33:11,237
Toque macaques attract one another's attention

278
00:33:11,407 --> 00:33:16,720
by fluttering their mauve eyelids
and flashing their teeth.

279
00:33:21,287 --> 00:33:27,044
Although there are many males,
there is a shortage of females ready to mate.

280
00:33:32,527 --> 00:33:36,520
Females are only fertile for a few weeks a year.

281
00:33:36,687 --> 00:33:40,839
During this period,
lots of males want to mate with them,

282
00:33:41,007 --> 00:33:43,475
but hierarchy does not allow that.

283
00:33:43,647 --> 00:33:49,882
This male, after years of political
manoeuvring and a good deal of muscle,

284
00:33:50,047 --> 00:33:54,677
has become alpha male, and he has first pick.

285
00:33:54,847 --> 00:34:00,399
Needless to say, there are always
some young males who try to beat the system.

286
00:34:00,567 --> 00:34:06,881
Booster has a lesser rank, which prevents
him from mating with a fertile female.

287
00:34:07,047 --> 00:34:10,562
His best chance is a secret liaison,

288
00:34:10,727 --> 00:34:13,366
but the alpha male has recruited allies

289
00:34:13,527 --> 00:34:17,918
and these males will stop
any female who tries to sneak away

290
00:34:18,087 --> 00:34:21,079
and reprimand her if necessary.

291
00:34:26,607 --> 00:34:32,443
This security team allows the alpha
to concentrate on his privileges.

292
00:34:37,927 --> 00:34:41,476
But Booster's chance has come.

293
00:34:41,647 --> 00:34:45,242
The allies don't have eyes
in the backs of their heads,

294
00:34:45,407 --> 00:34:50,879
and females - like Shanti here -
see Booster as a future alpha.

295
00:34:52,287 --> 00:34:58,157
Allowing him to father their children
could be a shrewd investment.

296
00:34:58,327 --> 00:35:03,845
First, she needs to attract Booster's attention.

297
00:35:04,927 --> 00:35:11,366
Shanti is flirting. Her glances are subtle
because she doesn't want to get caught,

298
00:35:11,527 --> 00:35:15,759
but they're unmistakable
if you know what to look for,

299
00:35:15,927 --> 00:35:19,397
and Booster certainly does.

300
00:35:19,567 --> 00:35:23,003
He needs to signal his intentions to Shanti

301
00:35:23,167 --> 00:35:29,402
but be able to feign disinterest
should the alpha male look his way.

302
00:35:33,007 --> 00:35:39,116
But the alpha has other females to attend to
and his allies are nowhere to be seen.

303
00:35:39,287 --> 00:35:42,882
Shanti gives Booster the eye.

304
00:35:51,447 --> 00:35:54,519
They must be discreet and quick.

305
00:35:54,687 --> 00:35:57,679
Shanti's absence will soon be noticed.

306
00:36:07,687 --> 00:36:12,681
If Booster takes over the troop,
he may look favourably on Shanti's young.

307
00:36:12,847 --> 00:36:15,680
They might, after all, be his.

308
00:36:24,047 --> 00:36:27,960
A big brain helps you
to take advantage of others,

309
00:36:28,127 --> 00:36:34,123
and the larger the group you live in,
the bigger your brain has to be.

310
00:36:37,207 --> 00:36:40,643
It was a dramatic change to the earth itself

311
00:36:40,807 --> 00:36:45,597
that allowed monkeys to climb
the next rung of the social ladder.

312
00:36:49,287 --> 00:36:53,599
Ten million years ago,
the climate of the world changed.

313
00:36:53,767 --> 00:36:56,804
Many places became much drier.

314
00:36:56,967 --> 00:37:02,837
The rainforests shrank and were replaced
by scrub and open grassland.

315
00:37:03,007 --> 00:37:06,761
There was a lot to eat
in this new kind of country

316
00:37:06,927 --> 00:37:10,397
and some monkeys came down
from the branches,

317
00:37:10,567 --> 00:37:14,196
and went out to find it in the open.

318
00:37:15,367 --> 00:37:22,478
The first monkeys would have found
some familiar foods - flowers and berries -

319
00:37:22,647 --> 00:37:27,641
but today baboons collect
all kinds of other things as well:

320
00:37:27,807 --> 00:37:30,924
bulbs, cactus, even rabbits.

321
00:37:34,327 --> 00:37:37,637
The grasslands
are a great place for an opportunist.

322
00:37:37,807 --> 00:37:44,758
Baboons use their nimble fingers and large
brains to collect an extraordinary variety of food.

323
00:37:44,927 --> 00:37:50,559
Insect grubs can be picked up from the edge
of a soda lake in Kenya's Rift Valley.

324
00:37:50,727 --> 00:37:55,596
Flamingos gather here
and generate a rich layer of compost

325
00:37:55,767 --> 00:38:00,602
that contains plenty of food
for those patient enough to pick through it.

326
00:38:00,767 --> 00:38:04,760
But a few baboons
have become more ambitious.

327
00:39:24,527 --> 00:39:27,997
Only this troop of baboons catch flamingos.

328
00:39:28,167 --> 00:39:32,763
It's just five years
since one discovered this new food

329
00:39:32,927 --> 00:39:34,918
and worked out how to get it,

330
00:39:35,087 --> 00:39:41,083
but the skill has spread, and now
the whole troop are dedicated flamingo hunters.

331
00:39:45,687 --> 00:39:49,646
Life in the open has its disadvantages too.

332
00:39:49,807 --> 00:39:55,962
There are more big predators around,
so baboons assemble in large groups.

333
00:39:58,287 --> 00:40:02,644
Living in big groups causes social problems,

334
00:40:02,807 --> 00:40:08,803
and here there's a complex social structure
within which males compete for females.

335
00:40:10,767 --> 00:40:17,036
When a female becomes sexually available,
her bottom swells and pinkens,

336
00:40:17,207 --> 00:40:23,680
but she only offers herself to males
who have looked after her the rest of the year.

337
00:40:28,087 --> 00:40:30,965
This male is attempting to join the troop,

338
00:40:31,127 --> 00:40:34,563
but it may be a while
before he can father offspring.

339
00:40:34,727 --> 00:40:39,084
First he has to learn the complex social order.

340
00:40:39,247 --> 00:40:45,004
A good way to start
is to befriend one of the senior females.

341
00:40:45,167 --> 00:40:51,163
The ledge can get crowded, and the presence
of the alpha male is intimidating.

342
00:40:52,527 --> 00:40:56,566
Even deciding where to sit is a political decision.

343
00:40:56,727 --> 00:41:02,563
The new male inevitably invades
the personal space of others. Tempers flare.

344
00:41:10,647 --> 00:41:13,400
(SCREECHING)

345
00:41:17,807 --> 00:41:21,800
Life for the new arrival can be very stressful.

346
00:41:24,487 --> 00:41:28,685
Established males rely
on a network of allies for support.

347
00:41:28,847 --> 00:41:33,318
The most successful
invested heavily in social relationships,

348
00:41:33,487 --> 00:41:37,878
but knowing who to build them with
takes intelligence.

349
00:41:38,687 --> 00:41:41,485
Grooming is a good way to maintain friendships.

350
00:41:41,647 --> 00:41:46,118
Looking after babies will also score you points.

351
00:41:47,367 --> 00:41:50,359
Child caring brings another benefit.

352
00:41:50,527 --> 00:41:56,045
Babies are protected in baboon society,
so no one will hit you if you're carrying one.

353
00:41:56,967 --> 00:42:03,486
That allows smart baboons to use infants
like shields when they feel threatened.

354
00:42:03,647 --> 00:42:09,643
It takes a lot of time and brainpower
to rise to the top in a large group.

355
00:42:27,407 --> 00:42:32,879
It's easy to imagine how a big brain
can help you thrive in baboon society.

356
00:42:33,047 --> 00:42:39,441
If social complexity is the driving force
behind the growth of the primate brain,

357
00:42:39,607 --> 00:42:45,398
then brain size in primates
should correspond closely to group size.

358
00:42:49,887 --> 00:42:53,197
This is the skull of a baboon,

359
00:42:53,367 --> 00:42:59,681
and this lump of plasticine represents
the brain which the skull once contained.

360
00:43:00,687 --> 00:43:06,284
This represents the brain of a bush baby.
It's essentially a solitary animal,

361
00:43:06,447 --> 00:43:11,396
but even allowing for its small body size,
its brain is tiny.

362
00:43:11,567 --> 00:43:17,085
This, slightly larger,
is the brain of a colobus. Group size - 15.

363
00:43:17,687 --> 00:43:22,920
This, bigger still, a guenon. Group size - 25.

364
00:43:23,087 --> 00:43:27,603
And back to our baboon. Group size - 50.

365
00:43:27,767 --> 00:43:30,804
In fact, the relationship is so close

366
00:43:30,967 --> 00:43:35,085
that were you to give a skull
to a monkey researcher -

367
00:43:35,247 --> 00:43:37,920
even though they didn't know the monkey -

368
00:43:38,087 --> 00:43:44,083
they would be able to accurately predict
the size of group in which it lived.

369
00:43:48,287 --> 00:43:51,757
500 miles away, in the highlands of Ethiopia,

370
00:43:51,927 --> 00:43:55,363
live the largest monkey groups of all.

371
00:44:04,007 --> 00:44:08,717
Geladas - the world's only grazing monkeys.

372
00:44:09,767 --> 00:44:13,680
There's a lot of grass here, so geladas flourish

373
00:44:13,847 --> 00:44:16,839
and gather into enormous herds.

374
00:44:17,007 --> 00:44:19,885
They don't have nipping teeth like sheep,

375
00:44:20,047 --> 00:44:23,517
so they have to collect their grass by hand.

376
00:44:23,687 --> 00:44:26,485
This is done best sitting down,

377
00:44:26,647 --> 00:44:32,517
and geladas spend much of their lives
shuffling along on their backsides.

378
00:44:37,087 --> 00:44:39,806
Because they're sitting down so much,

379
00:44:39,967 --> 00:44:45,485
their sexual displays are on their chests,
where other geladas can see them.

380
00:44:45,647 --> 00:44:49,242
These give an indication of strength and virility

381
00:44:49,407 --> 00:44:53,286
and allow individuals
to assess status at a glance -

382
00:44:53,447 --> 00:44:56,883
so avoiding unnecessary confrontations.

383
00:44:59,327 --> 00:45:04,401
Within these herds are smaller groups,
like those formed by other monkeys.

384
00:45:04,567 --> 00:45:10,437
Related females constitute the core,
with a male harem leader watching over them.

385
00:45:10,607 --> 00:45:13,599
And he has to be very vigilant.

386
00:45:17,887 --> 00:45:22,278
A pack of bachelor males
with one goal in mind -

387
00:45:22,447 --> 00:45:25,757
to displace the holder of the harem.

388
00:45:29,167 --> 00:45:35,640
The bachelors avoid males with the
brightest chests - they are in their prime.

389
00:45:43,327 --> 00:45:48,526
But less impressive males
will have to prove their worth in battle.

390
00:45:50,807 --> 00:45:54,004
A lip flip from a bachelor is a threat.

391
00:45:54,167 --> 00:45:57,398
Flip answers flip. There's going to be trouble.

392
00:46:06,807 --> 00:46:09,685
(SNARLING AND SCREECHING)

393
00:46:35,847 --> 00:46:40,204
The fights are largely for show
and rarely result in injury,

394
00:46:40,367 --> 00:46:43,564
but they do waste valuable grazing time.

395
00:46:43,727 --> 00:46:47,845
Eating grass is time-consuming
and occupies your hands,

396
00:46:48,007 --> 00:46:51,044
which makes it hard to find time for grooming.

397
00:46:51,207 --> 00:46:57,362
So geladas maintain their friendships
in another way - they chatter to one another.

398
00:46:57,527 --> 00:47:01,486
(BABBLE OF CALLS)

399
00:47:04,087 --> 00:47:08,444
These noises are, in effect, vocal grooming,

400
00:47:08,607 --> 00:47:13,522
and enable geladas to communicate
with many individuals at the same time.

401
00:47:13,687 --> 00:47:18,681
This is the secret of their ability
to live in huge groups.

402
00:47:21,287 --> 00:47:24,643
Their chatter sounds like a language,

403
00:47:24,807 --> 00:47:29,597
but we have no idea what sort
of information they're exchanging.

404
00:47:30,487 --> 00:47:33,285
One thing, however, is likely -

405
00:47:33,447 --> 00:47:38,965
the need to communicate detailed social
information between many individuals

406
00:47:39,127 --> 00:47:44,042
led to the evolution of language
in our own species.

407
00:47:46,847 --> 00:47:52,638
So although monkeys living in the tree tops
have rich and varied lives,

408
00:47:52,807 --> 00:47:57,039
it's the ones that came down
and formed large groups

409
00:47:57,207 --> 00:48:01,519
that have the most complex
and communicative societies.

410
00:48:01,687 --> 00:48:06,681
A fact not without significance
for our own ancestry.