Monkeys and apes are our closest relatives.
They have the richest social life of all mammals,
and much time is spent establishing relationships
and climbing the social ladder.
And that has had some remarkable consequences.
South America.
A few capuchin monkeys are having a morning get-together.
Capuchins are like the earliest monkeys, judging from fossils -
the basic pattern, you might say.
Their grasping hands and gripping tails
enable them to race through the forest with astonishing speed and agility.
But it's their big brains that really give them an edge.
One thing that's characteristic of monkeys
is their ability to spot an opportunity and then exploit it.
Of none is that more so than these capuchins.
They'll always grab a ripe fruit,
but they investigate everything. Little escapes them.
Their inquisitiveness really impresses you when you follow them.
They look for food everywhere.
Their colour vision is excellent, but their sense of smell is no better than ours.
So to find food that's hidden from view, they use not their noses, but their brains.
They can imagine what might be lurking beneath dry leaves.
Out of sight, for them, is not out of mind.
A good memory must help.
Recalling a previous experience makes the difference between getting stung
and getting honey.
The troop is just entering these mangroves.
Most mammals wouldn't find much to eat here,
but the monkey's big brain enables them to find things others miss.
Only the bolder ones chance their hand with crabs.
It's brave to tackle claws with delicate fingers.
The retreating tide also exposes shellfish, but eating those poses problems.
The clams are certainly full of meat, but it's locked behind closed doors.
However, grasping hands, guided by a big brain, can deal with that problem.
These clams are very tough. I'd have difficulty in opening them myself.
But these monkeys have learned that if you hit them long enough,
the clam relaxes, the shells can be opened, and they can get the meat inside.
The whole troop know the trick. Over 20 of them are giving the clams the treatment.
Ten minutes on, and the clam shells are still tightly clenched.
This is hardly fast food.
The young watch attentively. Most will learn how to do it,
so the technique will be passed to the next generation.
But it takes years for a young monkey to get it right.
Patience is important. Unfortunately, so is technique.
Capuchins, like us, have varied personalities and abilities.
Some never get to grips with clam cracking.
Those with a good technique and perseverance are now collecting their rewards.
Some aren't exactly thrilled by what they find.
It's not just food that monkeys collect from the forest.
These two bunches of leaves look much the same,
but this kind is used by the local people as an antiseptic and an insect repellent,
whereas this one has no medicinal qualities at all.
If I put them both down, I think I know which the monkeys will choose.
Those are pipa leaves - the ones with insect-repelling sap.
Pipa is usually hard to find, so this bunch will cause excitement.
Pipa rubbing is a major social event.
Those taking part disregard their differences and everyone joins in the party.
Do the capuchins know that this protects them
against skin infections and mosquitoes? It's impossible to say.
But it is the case that they do it more frequently during the rainy season -
when there are more mosquitoes around - than at any other time during the year.
Not all capuchins use pipa,
but once an individual discovers it, the knowledge spreads,
so pipa leaf rubbing becomes a group tradition.
Capuchins eat most things. Some monkeys, however, have specialities.
These are uakaris, and they will eat fruit of an unusual kind.
Their face colour indicates their social position.
The brighter the scarlet, the more senior the animal.
Such excellent colour vision also helps them to select their fruit.
Unusually, sakis are able to eat fruits that are vivid green and not ripe.
The monkeys here can all eat different foods,
allowing many species to live side by side.
The saki has special teeth to eat nuts that no other monkey can crack.
The spider monkey has long limbs and a grasping tail,
which enable it to collect the very ripest fruit.
But there are foods in this forest that not even a spider monkey can get to.
There's food for monkeys in every part of the rainforest,
but some of it is difficult to reach.
I've got up into the canopy in a crane, and I'm 120 feet above the ground.
Here on the outermost twigs,
the stems are so thin, they couldn't support a normal-sized monkey.
Yet there's a lot of food up here.
Underneath these leaves, a cocoon, a caterpillar, another leaf-eating insect.
But there is one kind of monkey that can get up here and catch these.
It's a pygmy marmoset.
The smallest monkey in the world - no bigger than my hand.
Its feet are too small to grasp anything but the thinnest twigs.
Their sharp claws prevent them from slipping.
As it stalks its insects,
it has to move with great stealth lest any vibration should scare them off.
But these hunters are so small that not even the thinnest branches tremble.
Monkeys have forward-pointing eyes with which to judge distance -
invaluable when moving around in the trees -
but this tiny hunter uses that ability also to pounce.
But their staple diet is more extraordinary.
You might think these lumps are a natural feature,
but in fact they're wounds, inflicted by pygmy marmosets
that come to this tree trunk every day.
It's eating gum which it's forced the tree to produce by gnawing its bark.
It's also making sure that there's going to be gum tomorrow
because it's also reopening the wounds that the tree has healed up.
The marmoset opens these wounds, the tree closes them,
until so much scar tissue builds up that mounds appear.
Generations of pygmy marmosets have done that on this particular tree,
resulting in these huge columns of lumps running right up the trunk.
A well-managed gum tree is a huge asset to a group of marmosets
and that makes it a tempting target for thieves...
..and a rival group is preparing to invade.
The intruders charge and the owners flee, leaving their precious gum undefended.
As the invaders steal the gum, the displaced residents start scent marking.
This seems to reinforce the bonds between them,
and they launch a counterattack.
(SCREECHING)
It works. The home team are back on their tree.
You can share a food resource that's cropped by others
without a face-to-face confrontation.
You might think that at sundown all monkeys are preparing to sleep.
That's almost true, but not quite.
Only one monkey in the world collects its food by night.
And precisely because it's nocturnal, it's seldom seen and still little known.
There's a family of them living in this tree. They're dourocoulis.
They're also known, for obvious reasons, as owl monkeys.
Their eyes may be huge but their night vision is not that good,
which suggests that their ancestors lived by day
and that dourocoulis became nocturnal comparatively recently.
During the day, the flowers on which they feed are guarded by other monkeys.
By coming out only at night, dourocoulis avoid having to fight for a share
and can feed in peace.
Day breaks.
The dourocoulis retire and other fruit and nectar-feeding monkeys awake.
Tamarinds set off to collect their share.
The forest is not rich in such food, and although tamarinds live in small groups,
finding all they need takes time.
The female always produces twins, which travel with the family.
She has two male partners.
Using her tongue, she signals that it's time one took over the twins.
Both are eager to do so.
Both mated with her, so each has cause to regard the babies as his.
But the twins have other ideas. They want to stay with Mum.
She gets rid of them at last, and it's important that she does.
She provides them with milk, so she must eat more than usual
and she would find that difficult if always burdened by her babies.
The situation is made harder because there are other kinds of tamarinds here.
This is one of them - a saddleback tamarind.
Monkeys usually guard food ferociously,
but these tamarinds often feed side by side.
And when one leaves, the other follows.
The emperors go first and the saddlebacks with their shorter legs try hard to keep up.
The travelling party shares a quick refuel.
Both kinds of tamarind, being small and energetic, need frequent snacks.
They share another thing - an enemy.
They give alarm calls to both species.
A tayra - a kind of giant weasel.
Not the most dangerous predator in this forest, but deadly to a small monkey.
It's certainly safer to travel in groups,
but sharing food is a high price to pay for a warning system.
There is, however, another more subtle advantage.
Each flower needs time to refill its reservoir of nectar
after a visitor has drunk from it.
If either tamarind followed separately, they might make a long journey
only to reach a tree that had been emptied by the other.
That would be disastrous for an animal that has to feed so regularly.
It's better for tamarinds to travel together and then share the food when they arrive.
Howler monkeys - ten times the size of a tamarind.
They also eat flowers, but these are not always available.
In tropical forest, at least leaves can be found all year round,
and howler monkeys specialise on these.
The best leaves are in the canopy,
so that's the best place to go to watch howlers.
Leaves are not all the same. Some are poisonous even to a howler monkey
and some edible ones are nicer than others.
Once again, that monkey ability to see in colour is a great help.
These red ones are young and succulent and would be very good to eat
if they weren't protected by poisons.
These mature ones are green and the poison in them has faded,
but they're fibrous and not very good to eat.
A leaf-eater wants something in between - like this.
Imagine how difficult it would be to pick the right one
if you didn't have colour vision.
Even the best leaves are not easy to digest,
so howlers spend a short time collecting their food,
but a long time digesting it.
In fact, they spend half of every day just lying around, like cows chewing the cud.
Even after all that digestion, leaves are not very nutritious.
Howlers can't afford to waste energy chasing away rivals.
They use a more labour-saving way.
(LOW WHISTLING)
(CACOPHONY OF HOWLING)
Howlers have a specially-enlarged bone in the throat - a hyoid -
that enables them to make this extraordinary song.
It's one of the loudest noises made by any animal.
The whole family joins in almost every evening.
They can work themselves up into quite a frenzy.
But since neither they nor their rivals move anywhere, it's hard to say who's winning.
It may be that howling serves to strengthen family solidarity and deter intruders.
(FAINT HOWLING)
(CROAKING CALL)
That may sound like a howler monkey, but I've now left South America, I'm in Africa.
That's the howler's African equivalent - the black and white colobus.
As in South America, many different kinds of monkeys share the same forest,
because they find their food in slightly different ways.
Red colobus have a special stomach and can eat unripe fruit and leaves.
Sooty mangabeys, like saki monkeys,
have extremely powerful jaws that can break open tough foods.
The other monkeys are more general in their diet.
and they belong to a group called the guenons.
All guenons eat fruit and insects, but each feeds at its own level in the forest.
There are 17 different kinds of guenon in Africa.
They all have similar shape bodies,
but each has its own colours and patterns that serve as social signals -
allowing them to recognise friends and rivals at a glance.
They're the most colourful group of monkeys in the world.
Colour signals are not a good way of sending messages
in places where the visibility is poor,
and that's certainly the case here in the Tai forests in West Africa.
If you miss a warning of danger, the consequences could be fatal.
How do monkeys keep out of harm's way?
I'm with one of the most extraordinary anti-predator alliances in the world.
Around me is a troop of sooty mangabeys and mongooses.
They are keeping an eye out for danger on the ground.
Above me, there are at least five or six other species of monkey
ready to detect a threat from the sky or from within the canopy.
In this alliance, monkeys of many kinds travel side by side.
It's a huge safety network that extends from the canopy
right down to the forest floor.
With so many pairs of eyes at every level, someone is almost certain to spot a threat,
no matter where it comes from.
There's little squabbling over food between species as each finds it in a different way.
Visibility is so poor that the monkeys communicate almost entirely by sound.
A sound reaches every monkey in a split second.
It's the best means of staying in contact or warning of danger.
Diana monkeys forage high up the canopy,
so they're usually first to spot danger from the air.
Crowned eagles are never far away.
If one comes too close, a specific alarm will be sounded
telling monkeys to drop for cover.
Danger above! Monkeys plummet down without looking up.
The alliance has saved another member.
All these monkeys have different alarm calls for different predators. Watch this.
(SHRILL CALLS)
(CROAKING CALLS)
(ECHOING BARK)
That's the leopard alarm call of the Diana monkey.
That totally different one is the spot-nose.
The point is that all species of monkey in the alliance recognise one another's call
and know the nature of the enemy.
That's important because each predator requires its own particular response.
All these monkeys now know that there's a leopard around,
so you might think they'd flee. But they don't. They're advancing towards it.
That's because the leopard is an ambush predator.
Once it's been spotted, it usually gives up.
Monkeys are drawn by the call.
They even drop lower and closer so they can keep the cat in full view.
And here they will stay on maximum alert until the leopard gives up
and leaves them in peace.
The ancient city of Polonnarwua in Sri Lanka.
The civilisation that built it a thousand years ago has long since crumbled.
But one society that lived here then is still here now, and thriving.
Toque macaques have walked these walls for centuries,
but only in recent decades have we started to understand their complex society.
This is one of the most studied monkey groups of all time.
For the past 30 years, their trials and tribulations have been recorded,
and that has given us remarkable insight into their lives.
These youngsters are playing as equals, but they have different futures ahead.
There's a ruthless class system in monkey society.
Those born into high-ranking families have a massive head start in life.
Imelda is one of them. She is high born.
Others have been feasting on berries, but she's arrived too late -
all the berries are in the cheek pouches of others.
Imelda spots Poppin. She's larger and older, but she's from a lower-ranking family,
and that entitles Imelda to take anything of Poppin's that she wants,
including the food right out of her mouth.
Poppin makes it as hard for her as she dare,
but if she resists too strongly, she risks a beating from the rest of the troop.
In monkey society, it helps to be high born, but it also helps to be intelligent,
and that is particularly apparent during the mating season.
Toque macaques attract one another's attention
by fluttering their mauve eyelids and flashing their teeth.
Although there are many males, there is a shortage of females ready to mate.
Females are only fertile for a few weeks a year.
During this period, lots of males want to mate with them,
but hierarchy does not allow that.
This male, after years of political manoeuvring and a good deal of muscle,
has become alpha male, and he has first pick.
Needless to say, there are always some young males who try to beat the system.
Booster has a lesser rank, which prevents him from mating with a fertile female.
His best chance is a secret liaison,
but the alpha male has recruited allies
and these males will stop any female who tries to sneak away
and reprimand her if necessary.
This security team allows the alpha to concentrate on his privileges.
But Booster's chance has come.
The allies don't have eyes in the backs of their heads,
and females - like Shanti here - see Booster as a future alpha.
Allowing him to father their children could be a shrewd investment.
First, she needs to attract Booster's attention.
Shanti is flirting. Her glances are subtle because she doesn't want to get caught,
but they're unmistakable if you know what to look for,
and Booster certainly does.
He needs to signal his intentions to Shanti
but be able to feign disinterest should the alpha male look his way.
But the alpha has other females to attend to and his allies are nowhere to be seen.
Shanti gives Booster the eye.
They must be discreet and quick.
Shanti's absence will soon be noticed.
If Booster takes over the troop, he may look favourably on Shanti's young.
They might, after all, be his.
A big brain helps you to take advantage of others,
and the larger the group you live in, the bigger your brain has to be.
It was a dramatic change to the earth itself
that allowed monkeys to climb the next rung of the social ladder.
Ten million years ago, the climate of the world changed.
Many places became much drier.
The rainforests shrank and were replaced by scrub and open grassland.
There was a lot to eat in this new kind of country
and some monkeys came down from the branches,
and went out to find it in the open.
The first monkeys would have found some familiar foods - flowers and berries -
but today baboons collect all kinds of other things as well:
bulbs, cactus, even rabbits.
The grasslands are a great place for an opportunist.
Baboons use their nimble fingers and large brains to collect an extraordinary variety of food.
Insect grubs can be picked up from the edge of a soda lake in Kenya's Rift Valley.
Flamingos gather here and generate a rich layer of compost
that contains plenty of food for those patient enough to pick through it.
But a few baboons have become more ambitious.
Only this troop of baboons catch flamingos.
It's just five years since one discovered this new food
and worked out how to get it,
but the skill has spread, and now the whole troop are dedicated flamingo hunters.
Life in the open has its disadvantages too.
There are more big predators around, so baboons assemble in large groups.
Living in big groups causes social problems,
and here there's a complex social structure within which males compete for females.
When a female becomes sexually available, her bottom swells and pinkens,
but she only offers herself to males who have looked after her the rest of the year.
This male is attempting to join the troop,
but it may be a while before he can father offspring.
First he has to learn the complex social order.
A good way to start is to befriend one of the senior females.
The ledge can get crowded, and the presence of the alpha male is intimidating.
Even deciding where to sit is a political decision.
The new male inevitably invades the personal space of others. Tempers flare.
(SCREECHING)
Life for the new arrival can be very stressful.
Established males rely on a network of allies for support.
The most successful invested heavily in social relationships,
but knowing who to build them with takes intelligence.
Grooming is a good way to maintain friendships.
Looking after babies will also score you points.
Child caring brings another benefit.
Babies are protected in baboon society, so no one will hit you if you're carrying one.
That allows smart baboons to use infants like shields when they feel threatened.
It takes a lot of time and brainpower to rise to the top in a large group.
It's easy to imagine how a big brain can help you thrive in baboon society.
If social complexity is the driving force behind the growth of the primate brain,
then brain size in primates should correspond closely to group size.
This is the skull of a baboon,
and this lump of plasticine represents the brain which the skull once contained.
This represents the brain of a bush baby. It's essentially a solitary animal,
but even allowing for its small body size, its brain is tiny.
This, slightly larger, is the brain of a colobus. Group size - 15.
This, bigger still, a guenon. Group size - 25.
And back to our baboon. Group size - 50.
In fact, the relationship is so close
that were you to give a skull to a monkey researcher -
even though they didn't know the monkey -
they would be able to accurately predict the size of group in which it lived.
500 miles away, in the highlands of Ethiopia,
live the largest monkey groups of all.
Geladas - the world's only grazing monkeys.
There's a lot of grass here, so geladas flourish
and gather into enormous herds.
They don't have nipping teeth like sheep,
so they have to collect their grass by hand.
This is done best sitting down,
and geladas spend much of their lives shuffling along on their backsides.
Because they're sitting down so much,
their sexual displays are on their chests, where other geladas can see them.
These give an indication of strength and virility
and allow individuals to assess status at a glance -
so avoiding unnecessary confrontations.
Within these herds are smaller groups, like those formed by other monkeys.
Related females constitute the core, with a male harem leader watching over them.
And he has to be very vigilant.
A pack of bachelor males with one goal in mind -
to displace the holder of the harem.
The bachelors avoid males with the brightest chests - they are in their prime.
But less impressive males will have to prove their worth in battle.
A lip flip from a bachelor is a threat.
Flip answers flip. There's going to be trouble.
(SNARLING AND SCREECHING)
The fights are largely for show and rarely result in injury,
but they do waste valuable grazing time.
Eating grass is time-consuming and occupies your hands,
which makes it hard to find time for grooming.
So geladas maintain their friendships in another way - they chatter to one another.
(BABBLE OF CALLS)
These noises are, in effect, vocal grooming,
and enable geladas to communicate with many individuals at the same time.
This is the secret of their ability to live in huge groups.
Their chatter sounds like a language,
but we have no idea what sort of information they're exchanging.
One thing, however, is likely -
the need to communicate detailed social information between many individuals
led to the evolution of language in our own species.
So although monkeys living in the tree tops have rich and varied lives,
it's the ones that came down and formed large groups
that have the most complex and communicative societies.
A fact not without significance for our own ancestry.