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Episode 3 of 3

Duration: 1 hour

In the final episode Dr Alice Roberts explores how our species, homo sapiens, developed our large brain; and asks why we are the only one of our kind left on the planet today?

The evolution of the human mind is one of the greatest mysteries. We are special because of our extraordinary brain, and to understand why we think and act the way we do, we need to look at where and why our brains evolved.

The Rift Valley in Kenya is thought to be the crucible of human evolution, and here Alice examines the fossils in our family tree which reveal our brains have more than quadrupled in size since our ancestors split from chimpanzees. Drawing on research on social politics in chimpanzees, the cognitive development of children and the tools that have been found littered across the Rift Valley, Alice explores how and why our ancestors brains became so big. It's thought their need to understand each other and share knowledge has fundamentally shaped the brains we live with today.

But our big brains came at a cost. Alice visits a maternity hospital to explore how our difficulties in giving birth are a result of our large brained babies, and travels to meet the women of the Hadza tribe to explore how looking after our large-brained children has shaped the life histories of all of us. Research suggests old age isn't a consequence of modern medicine, but an evolutionary adaptation to allow grandmothers to help raise their grandchildren.

Successive species of increasingly large brained humans migrated around the world - from Homo erectus to heidelbergensis, the Neanderthals to us. It's always been assumed the reason that Homo sapiens succeeded where others failed is to do with our large brains. But comparing skulls it's clear Neanderthals had just as big a brain as us. So why is there only us left? Alice goes to meet Svante Paabo, decoding the Neanderthal and human genome, and Clive Finlayson, who is unearthing the Neanderthals final settlement, to try to find out...

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  • Interesting facts

    • Your brain is the most complex organ in nature consisting of around 100 billion nerve cells.

    • An average sized human brain comprises about 1.4 kg of jellylike fat and protein.

    • Your brain uses about 300 kcal of energy per day. The equivalent of just a 15 watt light bulb.

    • Dolphins, elephants and other species have larger brains than humans, but we have the most developed cerebrum, giving us the greatest power for thought.

    • It’s not the size, it’s what you do with it: Einstein’s brain weighed less than average, but he had more neurons packed into his cerebral cortex than most of us.

    • As your brain developed in the embryo, your neurons travelled like tiny inch-worms along glial cell scaffolding to their final destinations. Some of these journeys of several mm were the equivalent of a human walking across the USA.

    • The brain of a newborn baby is only ¼ of its full size, while those of other Great Apes are already half grown at birth.

    • Because of this, the 22 bones of your skull were not fused at birth and overlapped each other to fit through the birth canal. Your brain was only fully grown after about eight years.

    • The cells you were born with will have virtually all been replaced many times over by the time you die. Only brain neuron cells and heart muscle cells last a lifetime.

  • BBC TV blog

    BBC TV blog

    Find out what Origins Of Us presenter Dr Alice Roberts discovered when she studied wild chimpanzees in the Ugandan forest: “they were all around us in the forest, and would often pass by very close, sometimes a metre or two away - which was both terrifying and exciting”

    Read Alice Roberts' full post on the BBC TV blog


Alice Roberts
Series Producer
Zoe Heron
Executive Producer
Sacha Baveystock
Paul Olding
Paul Olding


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