Fifty years after its discovery on November 24, 1974, in the Afar region of northeastern Ethiopia, the fossil known as Lucy continues to shape our understanding of human origins. Lucy remains an icon among prehuman fossils, representing humanity's deep evolutionary history in Africa and playing an outsized role in the investigation of human origins due to her value as a symbol and her intrinsic worth as a source of evidence about human evolution.
Lucy, a 3.2-million-year-old Australopithecus afarensis specimen, consists of 47 bones, constituting approximately 40% of a single skeleton. Discovered by American paleoanthropologist Donald Johanson and his graduate student Tom Gray, the fossil was unearthed during excavations in Hadar that began in 1973. The team celebrated the discovery around a campfire, with the Beatles' song "Lucy in the Sky With Diamonds" playing repeatedly, leading to the suggestion to name the fossil Lucy. She is also known in Ethiopia as Dinkinesh, which means "you are marvelous" in Amharic.
At the time, Lucy was the most complete hominin skeleton found from such an ancient period, which was unprecedented for a fossil approximately 3.2 million years old. Her skeleton is similar enough to modern humans for researchers to think she could be a close relative or even an ancestor of modern humans. Lucy helped piece together an evolutionary puzzle that, until then, was disordered and full of loose ends.
Lucy provided extensive information about early human ancestors. Among the preserved regions of her skeleton 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. This allowed scientists to determine that Australopithecus afarensis had limb proportions closer to those of chimpanzees and bonobos than to those of modern humans. Other fossils belonging to Australopithecus afarensis provide compelling evidence that the species walked upright on two legs, confirming that upright walking evolved before large brains in human evolution.
Since Lucy's discovery, many more specimens have been found, providing an exceptionally detailed record of this ancient species. The dating of Australopithecus afarensis fossils covers a period from approximately 3.8 to 3 million years ago. Until additional fossils of recently identified hominins are found, Australopithecus afarensis remains the most likely ancestor and one of the most important species in human evolutionary history.
Debates among scientists about Lucy's place in the human family tree continue. Some experts think Lucy belongs on the line leading to modern humans, adding to her significance. Potential descendants of Lucy have also multiplied, leading researchers to trace several possible lineages from her. The lack of information about Kenyanthropus platyops and other contemporaries leaves Australopithecus afarensis as the best candidate ancestor of Homo and Paranthropus, despite the increasing number of contemporaneous species, including Australopithecus bahrelghazali and Australopithecus deyiremeda.
Questions remain about whether Australopithecus afarensis or one of these other hominins is the ancestor of Homo and Paranthropus. The abundance of fossils led researchers Donald Johanson and Tim White, along with Yves Coppens, to propose the species name Australopithecus afarensis for Lucy and her relatives. Lucy's species possesses traits that foreshadow the genus Homo and others that belong to the paranthropines, placing it at the junction between two groups.
Tim White, an American paleoanthropologist, has been responsible for clarifying doubts regarding Lucy's significance. He explains, "These fossils represent our evolution. Lucy's lineage led to the genus Homo, the genus of our species." White notes that while debates continue, Australopithecus afarensis remains the best-studied species, with paleoanthropologists now recognizing the significance of having 400 remains of a species to analyze.
Pascal Picq, a member of the group of young scientists gathered around Yves Coppens, has focused on the craniofacial biomechanics and diet of Lucy. He notes that Australopithecus afarensis needed to be able to chew "bulbs, roots, tubers, and rhizomes," which are more perennial, due to changes in vegetation and the climate in East Africa. Picq offers another interpretation of the plethora of hominins uncovered in recent decades: "It is a mosaic evolution, with a diversity of anatomical combinations."
Brigitte Senut, a paleontologist, has studied Lucy's upper limbs and notes that Lucy's bipedality differs not only from that of chimpanzees but also from modern humans. She states, "I have always placed Lucy on a separate path. And even more since our discovery of Orrorin tugenensis, with its more human femur, even though it is much older. That doesn't necessarily mean it is our ancestor. But if Lucy is in that lineage, it implies an evolutionary yo-yo."
Despite differing opinions, Lucy has remained a solid reference in the study of human evolution. She has definitively freed us from a desire to find our origin in Europe, remaining the great marker of our African roots. Lucy demonstrated that human evolution was much more convoluted, with a denser and more robust family tree that encompasses several species that inhabited Tanzania, Chad, Kenya, and Ethiopia four million years ago.
The discovery of Lucy had a significant impact on paleoanthropology, forcing scientists to reconsider key details of human evolutionary history, including when and where humanity began and how extinct members of the human family were related to each other and to modern humans. Lucy's skeleton helped articulate all the findings that had been accumulating in Africa since the 1920s.
Lucy continues to be an icon, not just of science but also in the public imagination. The fortunate choice of her name contributed to this recognition. Rebeca García, a member of the Human Evolution Laboratory at the University of Burgos and specialist in postcranial skeletons, points out that all the recreations that have been made of Lucy "are very endearing," making it easy for the general public to empathize and relate to her.
Even today, articles and theses are still being written about her. As Tim White states, "Lucy added an important piece to that puzzle. Still, we cannot put her on a pedestal because we would ignore the ultimate goal of paleoanthropology." Rebeca García adds, "Science advances so much that we cannot even imagine what answers Lucy will bring in the future, but she will continue to be fundamental in the study of human evolution, probably for another 50 years."
She is an icon among prehuman fossils and a symbol of evolution in progress. As Pascal Picq recalls, "Lucy has definitively freed us from a desire to find our origin in Europe. She remains the great marker of our African roots."
Sources: Scientific American, Le Monde (Science), EL PAÍS
This article was written in collaboration with generative AI company Alchemiq