Fifty years ago researchers working in the Afar region of Ethiopia recovered a remarkable fossil of an ancient relative of ours. This specimen of a female hominin, or member of the human family, soon became the most famous fossil in the world. If you’ve ever had even a passing interest in human origins, you have probably heard of her. She goes by the name Lucy.
One of the reasons Lucy is special is that she is a recognizable skeleton, albeit an incomplete one. Another is that the skeleton is enough like our own for researchers to think Lucy’s ilk could be a close relative—and possibly even an ancestor—of modern humans. But Lucy is just one of many hominin fossils that have come to light since Charles Darwin surmised in 1871 that humans originated in Africa. Why does she play such an outsized role in the public imagination—and in the investigation of human origins? The answer lies as much in Lucy’s value as a symbol of humanity’s deep evolutionary history in Africa as in her intrinsic worth as a source of evidence about human evolution.
Let’s page back to Lucy’s era. Nearly 3.2 million years ago a diminutive human ancestor with a mix of humanlike and apelike traits was living in the Horn of Africa on a grassy landscape dotted with trees and shrubs. She was part of a richer community of primates and a much more impressive variety of mammals than live in that region today. There is no reason to think that Lucy was special in any way during her relatively short life. What made her special was what happened to her after she died.
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When an animal dies on an open landscape, away from a lakeshore or stream channels, the soft tissues—muscles and ligaments—are consumed by scavengers large and small. The bones of the skeleton soon separate and break up, and in a remarkably short time, only fragments of the skeleton are left. There is nothing recognizable to fossilize. If the animal dies close enough to a lake or stream, there is a very small chance that one or more of its bones and teeth will be covered by a layer of sediment. Not only will the bones be physically protected by the sediment from further damage, but also, under the right circumstances, they will be hardened by chemicals in the sediment. This process, called fossilization, gradually converts bones and teeth into bone- and tooth-shaped rocks.
But even if all this occurs, we are still a long way from that individual’s remains becoming a famous fossil. For that to happen, the sedimentary rock in which the bones were entombed needs to be exposed by erosion, a team of scientists and trained fossil hunters has to find those fossilized bones before they deteriorate beyond recognition, and the team must have the extensive resources needed to recover the many bits and pieces of the specimen that have been scattered across the landscape by the elements. The exceedingly slim odds of the bones and teeth of a single individual being preserved, fossilized, exposed, discovered and recovered make the Lucy skeleton an exceptional discovery. The number of such skeletons in the early stages of the human fossil record can be counted on the fingers of one hand.
Another reason Lucy is exceptional is that among the various regions of her skeleton that are preserved are substantial parts of the bones that reveal the length of the limbs: the humerus and radius in the upper limb and the femur and tibia in the lower limb. One of the biggest differences between modern humans and our closest living relatives, the chimpanzees and bonobos, is the relative length of the limbs. Whereas modern humans have long legs and short arms, chimpanzees and bonobos have long arms and short legs. Chimpanzees and bonobos also have relatively long forearms.
All four of Lucy’s main limb long bones are damaged or missing parts of the shaft, so their maximum length has to be estimated. Even so, enough of each bone is preserved to make it pretty clear that Lucy’s limb proportions—and thus the limb proportions of Australopithecus afarensis, the species to which she belongs—are closer to those of chimpanzees and bonobos than they are to those of modern humans. This is not to say that Lucy moved around like a chimpanzee or a bonobo: other fossils belonging to A. afarensis provide compelling evidence that the species walked upright on two legs. But it was practicing a form of bipedal locomotion that differed in significant ways from the bipedalism used by modern humans and our immediate predecessors. Whereas we Homo sapiens take longish strides when we walk, A. afarensis had a more lumbering gait because its feet were farther apart.
Some experts think Lucy belongs on the line leading to modern humans, adding to her cachet. But ancestry is difficult to demonstrate and almost impossible to prove with the patchy fossil record we have for early hominins. I know the difference between my ancestors—my parents, grandparents and great-grandparents—and my nonancestral close relatives, such as my uncles and aunts, and if I was not sure about anyone’s status, I could check using their birth certificates. There are no birth certificates in the fossil record, so we have to use shared morphology instead. The principle is that the more physical traits one species shares with another, the more closely related the species are, assuming that the morphology they share only evolved once in a recent common ancestor of the two species. We call this commonality shared derived morphology. But to return to my own family history, although I look more like my parents than a total stranger, once you go several generations into the past, my resemblance to my ancestors is not so obvious.
The fly in the ointment when using shared morphology to reconstruct relationships is a phenomenon known as homoplasy, in which different lineages evolve shared morphology independently rather than jointly inheriting it from a common ancestor. In this case, shared morphology is telling us more about shared environmental challenges than it is about shared evolutionary history. Still, even if A. afarensis is not our ancestor, it is very likely to be a close relative.
Lucy was found in 1974, almost exactly half a century after anatomist and anthropologist Raymond Dart had recognized the significance of a skull of a juvenile hominin found in Taung, South Africa. For three decades after the discovery of the Taung juvenile, the quest for human origins focused on southern Africa. That focus changed in the 1960s when paleoanthropologists Louis and Mary Leakey began to discover hominin fossils at Olduvai (now Oldupai) Gorge, in Tanzania, some of which looked as if they could even belong to our own genus, Homo. By 1974 that trickle of fossil discoveries in eastern Africa had become a torrent, with most of the finds coming from sites on the eastern shore of what is now known as Lake Turkana.
Not only had paleoanthropologists turned their attention from southern to eastern Africa, but the age profile of the most successful fossil hunters was shifting from senior researchers such as Louis and Mary Leakey, Phillip Tobias and Clark Howell to field workers such as Richard Leakey and Donald Johanson, who were even younger than Dart was when he recognized the significance of the Taung skull. Richard Leakey and Johanson were half the age of their predecessors—and telegenic to boot. Every high schooler or college student interested in human origins could imagine themselves in their place.
It was brilliant of Lucy’s discoverer, Johanson, to name the partial skeleton after a character in the popular Beatles song “Lucy in the Sky with Diamonds.” Lucy O’Donnell was a childhood friend of John Lennon’s son, Julian Lennon, who brought a drawing home from school one day and said it was Lucy in the sky with diamonds, inspiring the song. The name “Lucy” was a user-friendly way of referring to the A. afarensis skeleton that had the official catalog number A.L. 288-1. And the association with O’Donnell injected vitality and relatability into a collection of bone-shaped rocks.
But many things have changed since Lucy was named in the mid-1970s. For one, scientists are now more aware of the implications of the names given to fossils. Like John Lennon, Lucy O’Donnell was from Liverpool, England. Much of the Beatles’ success was based on its members’ authenticity as Liverpudlians. By the time of the Beatles, Liverpool was in economic decline, but in its heyday in the 18th century, it was the preeminent port in the U.K. The economic foundation of Liverpool’s prosperity came from the major role its merchants played in the trade of enslaved African people.
Lucy the fossil has another nickname. In Ethiopia she is known as Dinkinesh, which means “you are marvelous” in one of the country’s official languages, Amharic. As iconic as the name Lucy is, maybe it is time we all started to use Dinkinesh to refer to this extraordinary member of the human family.
