The Story of Lucy’s Discovery: How One Remarkable Fossil Changed Our Understanding of Human Evolution

Donald Johanson had no real reason to go searching for bones that particular Sunday. There was paperwork to handle, letters to write, and fossils to organize—tasks left unfinished as other paleoanthropologists visited his camp in Ethiopia’s Afar region.

But when graduate student Tom Gray prepared to map the fossil site at Hadar and needed a guide to Locality 162, Johanson decided to trust his instincts over his better judgment, joining Gray and the team in a Land Rover.

After two hours of searching, Johanson’s gut feeling had only led them to a few animal fossil fragments, and the temperature had already soared past 100°F. They made one final attempt at a nearby gully—still nothing—and called it a day.

As we were about to leave,” Johanson recalled, “I spotted something on the ground partway up the slope.” It was a 2-inch bone fragment that he instantly recognized as “part of an elbow.” But there was more: Upon closer inspection, he found pieces of a skull, a femur, a pelvis, and additional remains.

An extraordinary and almost impossible thought crossed my mind,” Johanson wrote. “What if all these pieces fit together? Could they belong to a single, incredibly ancient skeleton? No such skeleton had ever been discovered—anywhere.”

The camp was alive with excitement long before Johanson could answer that question. On the night of November 24, 1974, no one slept; beer flowed freely, conversation was endless, and a tape recorder played the Beatles’ “Lucy in the Sky With Diamonds” on repeat. By morning, the skeleton that would forever change our understanding of human evolution had been named: Lucy.

Walk Proud

Hadar, situated in the Awash River valley of the Afar region, is a vast, arid landscape of eroded sedimentary layers shaped by ancient rivers and volcanic eruptions. This unique geological history makes it a treasure trove of fossils. French geologist Maurice Taieb introduced Johanson to the site's potential for paleoanthropological discoveries when Johanson was still a Ph.D. student in the early 1970s, and together they embarked on their first expedition in the fall of 1973.

Johanson aimed to discover evidence of early species within a group now known as hominins, which includes all human species and their direct ancestors. Hominins (Hominini) belong to a tribe within the hominid family (Hominidae), which also includes chimpanzees, bonobos, gorillas, and orangutans, along with their immediate ancestors. Modern humans, Homo sapiens, are the only hominin species still in existence, and the full story of our evolution remains hidden in the fossil record.

One feature that sets humans apart from all other living mammals is our exclusive bipedalism—most of us (at least as adults) walk on two legs. In the mid-20th century, the dominant theory (a version of which Charles Darwin outlined in his 1871 work, The Descent of Man) suggested that hominins became bipedal after their brains grew larger and they began using tools. Simply put, walking on two legs frees the hands for other tasks.

However, during his first field season at Hadar, Johanson uncovered fossils that could challenge this narrative: a section of a tibia and two femur fragments that formed a knee joint at an angle, similar to modern humans. The fossils were estimated to be around 3 million years old, and their size indicated the creature stood only a few feet tall. This discovery suggested that hominins may have walked upright long before their brains grew significantly.

Putting walking aside, what type of hominin was this? A primitive Homo species—or something entirely different?

Found Kin

The story took an unexpected turn during the team’s next excavation at Hadar in 1974, which yielded three hominin jaws and, against all odds, Lucy.

Lucy’s significance lay in how well-preserved she was: hundreds of bones and fragments making up approximately 40 percent of a skeleton. Her wide pelvic opening indicated she was female, and the structure of her pelvis and legs confirmed she was bipedal. Standing about feet tall and dating back at least 3 million years (now estimated at nearly 3.18 million), Lucy had a small brain and a jaw that was distinctly smaller than the others found in the area. Because of these differences, Johanson speculated that Lucy belonged to a previously unknown species, while the jaws came from a different one.

However, further discoveries led Johanson to reconsider his hypothesis. One was the 1975 find of a complete set of hominin skeletons, known as the “First Family,” at Locality 333. “Fossils seemed to be pouring down the hillside like water from a fountain,” Johanson wrote. “A near-frenzy overtook us as we scrambled to collect them.” Another significant discovery came shortly thereafter, when Mary Leakey’s team uncovered fossils in Laetoli, Tanzania.

In the summer of 1977, Johanson and his colleague Tim White spent extensive time determining the scientific relationship between the fossils. Lucy, in particular, presented a challenge due to her small teeth, but the paleoanthropologists eventually concluded that this anomaly was likely due to sexual dimorphism—differences in appearance between males and females within a species. Standing at around feet and probably weighing about 60 pounds, Lucy was the smallest adult female in the collection, and her teeth reflected that. The largest individual measured 5 feet tall and could have weighed as much as 150 pounds.

Ultimately, they determined that all the fossils from Laetoli and Hadar belonged to a single species, which Johanson described as “somewhere between apes and humans and appearing to be neither one nor the other.” Their brains were fairly similar in size to those of chimpanzees, their arms hung a little lower than ours, and their faces had an ape-like appearance. Yet, they moved much like modern humans. Johanson and White categorized them under the genus Australopithecus, which had been named by Raymond Dart after his 1924 discovery of the Taung child, a hominin fossil that was also considered to be between ape and human (though Australopithecus loosely translates to “southern ape”). The species was named afarensis, in reference to the Afar region.

Lucy in the Rearview Mirror

At the time of her discovery, Lucy was the oldest and most complete hominin skeleton ever found, making her the symbolic representative of Australopithecus afarensis and the unofficial ‘mother’ of all humans. However, her legacy is much more complex, especially considering the many other fossils that have been unearthed since then.

For instance, we now know that Australopithecus afarensis was not the origin of bipedalism. Evidence shows that other hominins—such as the 4.4-million-year-old Ardipithecus ramidus, the 6-million-year-old Orrorin tugenensis, and possibly even the 6-to-7-million-year-old Sahelanthropus tchadensis—were walking upright long before Lucy. These findings suggest that bipedalism didn’t arise due to brain enlargement and may have even predated tool use. The earliest tools discovered so far are only about 3.3 million years old.

The reason why hominins began walking upright is still up for debate. One theory suggests it may have been driven by the need for males to carry food back to their mates, who were busy with childrearing. Another idea is that shrinking forests forced hominins to spend more time crossing grasslands, where walking on two feet was more energy-efficient than moving on four. There’s also the possibility that bipedalism developed as a way to adapt to life in the trees.

Another mystery surrounding Lucy is her connection to us. Fossils of other hominins that lived around the same time as Australopithecus afarensis have been found, including other species of Australopithecus like A. anamensis and A. deyiremeda, as well as Kenyanthropus platyops (though some suggest the lone fossil of this species could actually be another A. afarensis fragment). It’s commonly believed that Australopithecus eventually gave rise to Homo, with the oldest known Homo fossil—a jaw found in the Afar region in 2013—dating back to between 2.75 and 2.8 million years ago. Lucy’s species is often considered a strong candidate for being Homo’s direct ancestor.

“We have now discovered A. afarensis in Tanzania, Chad, Kenya, and Ethiopia, and we know that Lucy and her kind must have inhabited these parts of Africa for nearly a million years. This ancient age and broad geographical presence make me believe it is the most likely species to have given rise to the many species of the Homo genus and ultimately to our own species, Homo sapiens,” paleoanthropologist Zeresenay Alemseged shared with The Guardian in June 2024. However, this remains far from certain.

But Lucy’s impact goes beyond just our ancestry: She sparked an unprecedented public interest in paleoanthropology. In the 1970s, when Johanson explained to a Paris customs officer that the “strange little parcels” in his suitcase contained fossils from Ethiopia, the agent’s eyes lit up. “You mean Lucy?” he asked. A crowd soon gathered as Lucy’s bones were carefully laid out on the Customs counter. Johanson recalled, “It was my first hint of how much interest Lucy would generate from that moment onward.” This fascination was even more pronounced within the scientific community.

“One of the greatest effects of Lucy’s discovery was that it inspired so many scientists to venture out and search for more fossils like hers,” paleoanthropologist Yohannes Haile-Selassie remarked at a symposium celebrating the 50th anniversary of Lucy’s discovery earlier this year. Lucy wasn’t the final answer to humanity’s origins—she was just the starting point for an ongoing quest.