Horizon: What Makes Us Human?, BBC Two

Teamwork, as the song once said, makes the dream work. Homo sapiens knows this, if not quite by nature, then at least by nurture. Turns out that there are some chimpanzees in Leipzig which are all over the team thing too. Offered the chance to pull together on a simple mechanism to retrieve a nut – one each – two chimps will work in tandem to make it happen.

Perhaps these are just highly efficient Teutonic chimps who uniquely understand the meaning of Vorsprung durch Technik. But no. That stat about sharing 98 per cent of our DNA with chimpanzees? It seems the ability to cooperate is part of the 98 per cent. So, asked a pregnant Professor Alice Roberts in this edition of Horizon, what happens in the remaining two per cent that we don't share with the other apes?

Why release offspring into the world who can’t stand up for a year or be trusted with a front-door key for 18?

Share is the operative word. Still in Leipzig, Roberts was soon dropping in on some children who, set a similar experiment, will instinctively do something chimps can't: think selflessly. Human infants will work as a team to retrieve the treat, but share the spoils if one ends up with more than the other. This is why childbirth, explained Roberts, is rather more arduous for human mothers than their sister apes. The price of being the cleverest homonid is a large head to encase a phenomenally complex brain, requiring females to have hips wide enough to let all that thinking power pass through their dilated cervix, which still needs to be small owing to humankind’s tendency to get about on two legs.

This is the obstetric dilemma, suggested a scholar in Rhode Island. Women in labour may opt for fewer syllables to describe the agonising price of all that braininess. Roberts wandered about a maternity ward listening to the screams and for a moment the beatific smile she can summon up at will for the cameras slightly faded.

The next question: why nine months? Why release offspring into the world who then can’t stand up for a year and can’t be trusted with a front-door key for 18? It was cogently argued that the womb hangs on to its prize as long as it can until the placenta is no longer able to supply the foetus with enough sustenance to maintain its rate of growth. And when the child does take its first breath, it is still dependent enough on its mother to allow the long process of cultural nurture – learning how to share, to tie shoelaces, to eat with a knife and fork, eventually to make documentaries about chimpanzees – that is denied to the planet's other apes. Even in Leipzig.

After that it all got a bit microscopey as Roberts went into the lab to talk to brainiacs about DNA printouts, neural pathways and other computer-generated arcana. Those of us insufficiently nurtured towards a basic scientific qualification started to switch off, figuratively if not actually. But no matter. One will happily watch the mumsily beguiling Professor Roberts recite the phone book or explain knitting patterns or, as she did here, carve up a brain. We even got to meet her new baby at the end, fresh from the womb and raring to learn. Head didn't look too big.

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