Scientists at the University of Texas think they know how Lucy, the famous female of prehistoric times, met her death, writes Richard Collins.
Writing in the current edition of Nature, they claim that she fell from a tree and died from her injuries. If that’s right, they will have helped answer an intriguing question; when did our ancestors come down from the trees?
On the morning of November 24, 1974, Donald Johanson, the leader of a Franco-American research team, came upon scattered human-like bones in a gully close to the Awash River in Ethiopia. It took three weeks to gather up all of the fragments.
The bones, it turned out, belonged to a single individual, 40% of whose skeleton was recovered. The pelvic bone suggested that the creature, just over a metre tall, had been female. She was nicknamed Lucy after ‘Lucy in the Sky with Diamonds’ by the Beatles, which was popular at the time. The strata from which the remains came suggested that she had lived around 3.2m years ago.
Lucy’s brain was only the size of a chimpanzee’s but she was no ordinary great ape. The leg bones showed that she stood upright and walked the way we do. The arm bone between the shoulder and the elbow is relatively short in humans; about 72% the length of the thigh bone. In the chimpanzee, our nearest relative, it’s virtually as long as the thigh.
Lucy’s humerus, at 85% femur length, was intermediate between the two. There were other ‘half-way’ traits. Although she may have been on the evolutionary line leading to us, Lucy could not be admitted to the human club. Her species was named Australopithecus afarensis, ‘the southern ape from afar’.
The find made headlines all over the world. Lucy’s remains were taken on a controversial tour of the US before being deposited at the National Museum of Ethiopia in Addis Ababa, where they are today. She is not on public display there; a plaster-cast copy of the skeleton is exhibited.
The Texas University scientists, having CT-scanned every one of Lucy’s bone fragments, claim to have identified “fractures in multiple skeletal elements”. Her upper right arm, shoulder, and knee were badly injured, showing that she had fallen “from a considerable height”, “probably out of a tall tree”. The accident would have damaged her internal organs.
“Together, these injuries are hypothesized to have caused her death.” This offers “unusual evidence for the presence of arborealism in this species” , the researchers suggest.
Today’s great apes, the gorillas chimps and orangutans, remain forest-dwellers. Exiting the trees and moving out on the open savannah was a pivotal decision of our pre-human ancestors. They shed their hair, developed their sweat glands, and began walking upright, using the air to cool their bodies. Raised high above the scorching sun-baked earth, their energy-guzzling brains could grow larger without overheating. Vulnerable, slow-moving, without defensive claws or powerful teeth, Lucy’s kind relied on their wits to survive.
Her fall from a tree suggests that the bond with the forest had not been severed 3m years ago. Perhaps, at that stage of their development, our ancestors climbed into trees to avoid large predators at night. Did Lucy fall because, increasingly adapted to living on the ground, her species could not longer climb safely?
Are the Texan scientists reading too much into limited data? Some commentators think so. “Elephant bones and hippo ribs appear to have the same kind of breakage, but it’s unlikely they fell out of a tree,” Donald Johanson told the New York Times.
Palaeontologist Marc Meyer, who examined her remains, says “Lucy’s spine does not come close to the amount of damage we would expect to see in a fatal fall”.
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