The power of thought: Why humans have larger than average brains

Walking upright allowed habilis to start developing craftwork skills. Carpentry or stone sculpting requires very precise hand-to-eye co-ordination. Skills like these need well developed motor-neurone skills and sophisticated hand and finger co-ordination – processes that probably encouraged the evolution of bigger brains. Recent studies have shown that relative to other mammals, Homo habilis had a brain at least four times larger than it should have been for his size and weight.

Bigger brains use lots of energy. To power our brains we need about 20 watts of energy, or 400 calories a day – that’s about 20 per cent of our total energy consumption – just to be able to think. There’s a good deal of truth in that old expression “food for thought”. So began a most important evolutionary spiral.

Big brains need lots of energy, which is best supplied by eating meat. The most successful means of getting meat is by hunting for it, using tools and weapons. The creatures that were most well adapted to making such tools were those with the biggest brains. An avalanche of evolutionary changes kicked in, all thanks to Lucy’s fortuitous swivel up on to her two feet. These were adaptations that led, almost inevitably, to hunting, weapons, tools and intelligence, to the genus Homo, the species habilis and beyond. Some of Lucy’s ancestors stayed in the trees, so they didn’t need to bother with walking upright.

They evolved into today’s chimpanzees and bonobos. Without free hands, the evolutionary spiral that led to bigger brains and modern human intelligence never took off and their brains stayed small. After all, if you don’t need a bigger brain to survive, don’t have one. It’s far more energy-efficient.

Chimps and humans are genetically so close because these evolutionary changes happened so recently – probably no more than about 4 million years ago. Despite this short space of time, a big difference has emerged in terms of intelligence and brain size. An apparently simple change in circumstances, such as having freely available hands, seems to have triggered an evolutionary revolution. But just how big is the difference between humans and their closest animal relatives? Chimps, like gorillas, have been known to communicate. Kanzi (see picture, previous page) is a bonobo ape, born in 1980, who now lives in Georgia, USA. He can understand more than 3,000 spoken English words, many more than Koko the gorilla (see Part 3). When Kanzi wants to “talk” back, he points to a series of pictures so he can be understood by humans. It was reported in November 2006 that Kanzi was taken for a walk in the woods after having touched the symbols for marshmallows and fire. Once in the woods, he then proceeded to snap twigs and make them into a pile, light a fire and toast his own marshmallows on a stick.

One step further: How Africa became the cradle of all humanity

Most African people today are desperately poor and suffer terribly from disease, poverty, famine and war. You’d think there was good reason to flee – and they do. Thousands of Africans try to escape the continent each year, many of them across the Straits of Gibraltar into Europe. History is repeating itself.

About 2 million years ago Homo habilis had evolved into a new species of human, Homo erectus, who looked much more like us Homo sapiens today. For a long time, experts thought that the ancestors of modern humans originated in China, or maybe Java, because that’s where the bones of Homo erectus were first discovered, dating back at least 500,000 years.

Now, thanks to the discovery of a 10-yearold boy mysteriously swept to his death in an African swamp near Lake Turkana in Kenya some 1.8 million years ago, we know that he first appeared in Africa at just about the same time as Homo habilis died out.

Turkana Boy was found in 1984 by a team of fossil-hunters led by Richard Leakey, a British palaeontologist who lives in Africa. The implications were far-reaching, as Leakey himself explained soon after the find: “In 1984, his bones were painstakingly excavated to reveal a species on the brink of becoming human. All people on Earth have one thing in common. We share a single African ancestor; the same as this young boy.”

When alive, Turkana Boy was blackskinned and sweaty. His kind, Homo erectus, had lost their body hair because of the blistering African heat, which meant there was no need for fur. Dark skin and sweat glands helped these early people survive the harsh, arid heat of the African grasslands. Like us, Turkana Boy would have had hair on his head as a natural sunhat. A decent crop on top protects upright walkers from the Sun’s burning ultraviolet rays.

The boy had a long, protruding nose unlike his habiline ancestors, again useful for helping cool the blood. His pelvis shows that he walked more upright, and his skull shows a marked increase in size: now as big as 1,100 cubic centimetres, nearly twice the size of habilis.

Unlike his evolutionary ancestors, who sometimes fell victim to a hungry cheetah or a pouncing lion, erectus was the first human to make spears. In a contest with wild beasts, he almost always won.

Fire and language: what shills did humanity's early ancestors possess?

Homo erectus had several key advantages over anything else alive in the wild: his hands, his brains and, perhaps most important of all, his control of fire. This would have helped scare away the large animals that so bothered his ancestors. It also meant that Homo erectus eventually became the world’s first cook. Well before they became extinct, 70,000 years ago, these early people had figured out that cooked food releases energy more quickly than raw meat. It also takes less time to digest. The remains of human campfires nearly 1.5 million years old have been found in Africa and Asia (man-made fires magnetise the soil leaving tell-tale signs of human kindling).

Who taught man how to light a fire? How did he learn to control it? The ancient Greeks had a myth that tells the story of a Titan called Prometheus, who stole the fire of the gods and smuggled it down to Earth in the stalk of a fennel plant. He paid dearly for his crime. When the king of the gods, Zeus, found out, he had Prometheus tied to a rock. Each day an eagle was sent to pick out his liver. Each night his liver would grow back so that it could be picked out again when the eagle returned.

Zeus also took his revenge on man for gaining the knowledge of how to use fire. He sent a box down to Earth along with a pretty girl called Pandora, who was told never to open it. Of course, temptation eventually got the better of her, and when she lifted the lid suffering and despair were unleashed upon mankind for ever.

Fossil evidence shows that Homo erectus mastered the art of making fire by using stones. Pieces of scorched flint dating back 500,000 years have been found at several of their campsites located in northern Israel.

Homo erectus lived in groups of about 100, hunting together using sharpened flints, following wherever the scent of blood led them, chasing and trapping wild animals for food. Their tools were more sophisticated than those first made by the habilines. The biggest difference was that axes were worked on both sides of the blade into a sharp point. These “biface” tools have cutting edges up to four times bigger than those of the older technology, ideal for hacking wood, digging out roots, butchering animal carcasses and skinning hides. .

Could Homo erectus talk? Scientists think Turkana Boy’s bones suggest that he could not because the nerve openings in his vertebrae were not large enough to contain the complex nerve systems needed to control breathing required for speech. Maybe he developed a sign language of some kind, or perhaps something similar to modern-day texts? F we cn gt by ths wy, I hve no dbt thy cld 2.

With their portable toolkits, the protection of their communities and the magic of fire, these were people who were ready to walk wherever needs must to make sure that they were fed. Homo erectus was the first human species to explore life outside Africa – humanity’s first migrants; Africa’s ancient Marco Polos. inevitably, to hunting, weapons, tools and intelligence, to the genus Homo, the species habilis and beyond. Some of Lucy’s ancestors stayed in the trees, so they didn’t need to bother with walking upright.