BBC Sounds, Music, Radio, Podcasts.

They're all such, such different personalities.

One of the females, some arching orangutan, Subis, I've always had a very close relationship with.

She's got a reputation for being quite feisty,

but I quite like that, and we've always got on quite well.

This is the voice of the zookeeper who looks after the orangutans at Chester Zoo.

Martha, obviously, you can't not love Martha.

I mean, she's one of the oldest on record, so she's quite an old lady at 58.

She's got way more life experience than I've got,

and she's taught me more about orangutans

that I could ever have learnt from anybody else.

So for sure, they have the full range of human emotions,

and they're very intelligent,

and that includes emotional intelligence.

Look into an orangutan's eyes and you will see an expressive and curious creature looking right

back at you. Like us, they have tantrums. They seek cuddles for comfort and they get grumpy when

they're hungry. They are strikingly human.

And that similarity is what led some researchers to a bizarre question. Do orangutans have a midlife

crisis? I'm Hannah Fry, a mathematician who studies patterns in human behaviour.

And from BBC Radio 4, this is Uncharted, tales of data and discovery.

This is a series about how numbers and graphs can help you to map the invisible,

about how plots can be rich with hidden depths and unheard stories,

...