Groups of mothers and their young, a harem,
gather together to form troops of up to 800 monkeys.
Geladas' hands are usually busy plucking grass instead of grooming,
so to keep in touch, geladas have become the chattiest of all monkeys.
The gossipy banter can sound to scientists
like sentences with words or even names for each other.
Most agree it's often used to defuse tension.
And in geladas, there's a lot to be tense about.
There are gangs of young males
trying to steal away the women from the family harems.
Each handful of females is guarded by a single male, the harem master.
The spare boys try and tempt the girls away,
hoping the resident father figure doesn't notice.
The male's flash teeth at each other.
They may fight, but it's usually just showing off
in case the girls are watching.
There's a lot of flirting on both sides.
And then if an innocent-looking female is tempted to wander off past her guardian,
he has to decide what to do.
Girls mostly sneak off secretly for affairs.
This is a blatant challenge to his authority.
The illicit couple just sit.
The suitor seems to be using his hand to hide his grimace.
He probably doesn't want trouble.
Chimps, baboons and macaques may also try to look innocent
when they break the rules.
This is a complicated social problem.
Using your brain to control societies is called Machiavellian intelligence
after a 16th-century courtier who wrote on manipulating political power.
Instead of launching into an attack, the politician here tries to grab a baby.
Monkey etiquette dictates nobody attacks anyone holding a baby,
so they're like living flak jackets.
The mothers are worried and quickly scoop up the youngest.
Here, the two males face each other.
The family man backs towards one of his more loyal wives,
calling for support.
One of the youngsters suddenly switches from mother to father.
This should calm things down
With the youngster attached, the father's protected,
and the harem should unite.
But it can go wrong.
The youngster is slipping off. The family are frantic.
The harem master has no protection from attack.
The bachelor is finally driven off with a little help from the mothers.
But the fathers are meant to guard the precious young.
He knows he's in all sorts of trouble.
If the infant dies, the mothers may not support him again.
Our brain, too, wrestles with our own similar problems.
We are as social and as competitive.