By Simon Usborne
It was 1974 and Dr Donald Johanson and his student, Tom Gray, were heading back to camp after a fruitless morning searching for fossils in the scorched ravines of Ethiopia’s Afar Depression. Then something in the dust caught Gray’s eye. It was part of an arm, immediately recognisable as hominid, or human-like. As the American paleoanthropologists looked further, they spotted fragments of a skull, thigh, ribs and jaw.
Bone sightings in the Awash valley, one of the world’s most fertile fossil fields, are not rare. But Johanson and Gray knew that they had struck paleontological gold. After three weeks of painstaking excavation, the pair had recovered 47 bones, for a skeleton 40 per cent intact – the most complete remains of a human ancestor at the time. During the celebrations back at camp that first night, The Beatles’ “Lucy in the Sky With Diamonds” came on the radio, and the jubilant scientists christened fossil AL 288-1 “Lucy”.
Thirty-three years on, Lucy remains the world’s most famous fossil. The 3ft 8in female, who roamed the Awash Valley 3.2 million years ago, will go on show at the end of the month at the Houston Museum of Natural Science, making her first journey out of Africa.
Lucy’s importance in humani-ty’s quest to chart its own origins cannot be overstated. “In those days we were trying to determine which came first, out of the things that make us human,” says Dirk Van Tuerenhout, the curator of anthropology at the Houston museum. “Did we walk upright, use tools or have a large brain first?”
Many experts saw the answer in Piltdown Man, a skull unearthed in a Sussex gravel pit in 1912. It appeared to confirm what was then the prevailing notion: that humans had originated in Europe, and, as indicated by Piltdown’s large cranium, that our evolution had been led by our brains. But in 1954, Piltdown was revealed as a hoax, the aged skull of a modern man joined to the jaw of an orang-utan.
Lucy’s discovery 20 years later helped put scientists back on track. From the bones, Johanson and Gray determined that, like a chimpanzee, Lucy had a small brain, long arms and short legs. But, crucially, the structure of her pelvis and knee showed that she routinely walked upright on two legs. It was this discovery, coupled with a primitive skull, which confirmed that humans learned to walk before they became intelligent or made tools.
It’s not always so easy to pin discoveries on the map of human evolution. In 2003, Australian scientists on the Indonesian island of Flores unearthed the skeleton of a hominid that walked the Earth 18,000 years ago, thousands of years after it was thought our ancestors had become extinct. The diminutive hominid, nicknamed Hobbit, threatened to rewrite history, but while debate about its origins continue, several recent studies suggest the fossil is in fact a modern human whose tiny head was a symptom of the congenital disorder microcephaly. In fact, as scientists have begun to fill in gaps in the line linking Lucy to modern man, they are finding it isn’t a line at all. “Many of our early ancestors lived side by side,” says Van Tuerenhout. So intertwined is human lineage that some scientists say our “family tree” is more a “family bush”.
So how did Homo sapiens, who emerged about 200,000 years ago, rise as the only surviving human species? To answer that, we must return to Ethiopia and Lucy.
We know that Lucy and the rest of Australopithecus afarensis had become extinct by about three million years ago, a victim of climate change on a devastating scale. A tilt in the Earth’s axis cooled the planet, destroying the lush forest that Lucy relied on. Species had to adapt or die. One early example is a hominid called Paranthropus boi-sei, which evolved a large jaw, huge chewing muscles and strong back teeth ideal for eating tough nuts and roots. But Homo habilis, which lived alongside Paranthropus boi-sei, had a smaller jaw and teeth. So it evolved into a scavenger, feasting on the discarded carcasses of antelope and wildebeest. Meat turned out to be much easier to digest, allowing Homo habilis to divert energy to the brain, the size of which, in evolutionary terms, can be linked to intelligence.
His brain fuelled by calorie-packed meat, it was not long before early man realised that by knocking stones together he could create a sharp edge. By cutting into bone, habilis could then extract bone marrow, an even more nutritious “brain food”. The vegetarian specialist soon perished, leaving Homo habilis to grow stronger and smarter – and, soon, to leave Africa.
Scientists still debate where Homo sapiens first emerged. The prevailing theory is that humans left Africa about 50,000 years ago. We know for sure that the first hominid species truly recognisable as human, Homo ergaster, originated in Africa about two million years ago. A Homo ergaster skeleton, called Nariokotome Boy, was discovered in Kenya 10 years after Lucy (who had lived almost a million years earlier). The bones showed evidence of many human characteristics, including the ability to regulate temperature by sweating, vital for allowing ergaster to travel long distances as it scavenged for meat.
Ergaster also evolved a narrower pelvis, more efficient for lengthy missions in search of food. This led to the narrowing of the female birth canal, already under pressure in childbirth from the growth in brain size. The evolutionary solution was for humans to be born with relatively underdeveloped brains. As a result they needed more nurturing than their chimp ancestors, whose young were born with almost mature brains. Experts say that, triggered by man’s need to walk in search of meat in a changing climate, this led to the birth of the nuclear family.
So the scene was set for humans to dominate the planet, brilliantly adapting to thrive in myriad environments in their search for food. The extinction of Neanderthals about 28,000 years ago left Homo sapiens as the sole hominid species on the planet. By then we had developed even bigger brains and more advanced tools, and became hunters. Van Tuerenhout says that modern man’s wanderlust and capacity to reproduce has done much to insure the species against extinction. “If a giant cataclysm were to kill three million people, it would-n’t endanger the species,” he says.
There are subtle ways in which we continue to change. Our little toes were once vital for climbing trees, but might soon disappear, along with our appendices and wisdom teeth, vestiges of our vegetarian past. Van Tuerenhout points to the arrival of agriculture around 10,000 years ago as one of the most important factors in modern human evolution. “We now have plenty of food, but we still eat as though famine might come tomorrow,” he says. As a result, we store excess food as fat, damaging our health. “This could shape the way we evolve because if we drop dead before we have children, there goes our contribution to future generations,” he says.
What of the future? Will the anthropologists of a new species of human one day study the demise of Homo sapiens? Van Tuerenhout thinks we are too successful at adapting and travelling to evolve into a new species. The only circumstances in which a new species of human might emerge is if, having stepped out of Africa hundreds of thousands of years ago, we might then step out of this world. “If we ever managed, in large enough numbers over a long enough period of time, to leave our planet and start colonising other areas of space,” he says, “the new environmental pressures, be they gravity or different solar radiation, could see the evolution of a new species.”
Lucy’s cranium owes much to her simian ancestry. She must have had a small brain – and humans must have evolved bigger brains only after we learnt to walk upright.
Though not recovered completely intact, Lucy’s remaining vertebrae showed evidence of spinal curvature, which helped to confirm that she walked upright.
The talus bone in her ankle showed signs that Lucy had a developed big toe. This meant she couldn’t grip things so well with her feet, but that she could walk more efficiently.
Lucy’s long arms and fingers showed that she was still equipped to swing in trees, perhaps to escape the predators she was evolving to compete with.
The structure of Lucy’s knee and hip joints show that she walked upright, making her the oldest fossilised remains of a human ancestor