On the Origin of Lucy: How One Extraordinary Fossil Helped Alter Our View of Human Evolution

Donald Johanson really had no business going bone hunting that Sunday. There were letters to write and fossils to catalog—heaps of paperwork left undone while fellow paleoanthropologists were visiting his camp in Ethiopia’s Afar region.

But graduate student Tom Gray was headed out to map the fossil site, Hadar, and he needed a guide to Locality 162. So Johanson ignored his better judgment in favor of what he later called a “gut sense” and set off with Gray and company in a Land Rover.

A good two hours into the search, that gut sense had only netted them a handful of animal fossil fragments, and the late-morning temperature had already topped 100°F. They made one last sweep of a peripheral gully—nothing doing—and decided to call it a day.

Then, “as we turned to leave,” Johanson recalled, “I noticed something lying on the ground partway up the slope.” It was 2-inch-long bone shard that he immediately recognized as “part of an elbow.” And it wasn’t alone: A closer scan turned up bits of a skull, a femur, a pelvis, and more.

“An unbelievable, impermissible thought flickered through my mind,” Johanson wrote. “Suppose all these fitted together? Could they be parts of a single, extremely primitive skeleton? No such skeleton had ever been found—anywhere.”

The camp buzzed with the thrill of a big break long before Johanson could answer that question. That night, November 24, 1974, nobody slept, beer flowed as freely as conversation, and a tape recorder blared the Beatles’ “Lucy in the Sky With Diamonds” on repeat. By morning, the skeleton that would forever alter our understanding of human evolution had a name: Lucy.

Walk Tall

Hadar, located in the Afar region’s Awash River valley, is a dry expanse of eroded sedimentary deposits formed in part by prehistoric rivers and volcanic eruptions. Thanks to its geological backstory, it’s a fossil gold mine. French geologist Maurice Taieb put Johanson on to the site’s paleoanthropological potential when Johanson was still a Ph.D. student in the early 1970s, and the two teamed up for their inaugural expedition during the fall of 1973.

Johanson hoped to find evidence of early species in a category now commonly known as hominins, which includes all human species and their immediate ancestors. Hominins (Hominini) are a tribe (i.e. a subgroup) of the hominid family (Hominidae), which also features chimpanzees, bonobos, gorillas, and orangutans, as well as their immediate ancestors. Modern humans are Homo sapiens, the only hominin species that exists today, and how exactly we evolved as we are is buried deep within the fossil record. 

One characteristic that makes humans unique among extant mammals is that we’re exclusively bipedal—most of us (as adults, anyway) always walk on two feet. In the mid-20th century, the leading theory (a version of which Charles Darwin had laid out in 1871’s The Descent of Man) posited that hominins evolved this way after their brains got larger and they started using tools. To put it very simply, walking upright leaves your hands free to hold things.

But during his first field season in Hadar, Johanson unearthed fossils that could complicate this timeline: part of a tibia and two femur pieces that formed a knee joint at an angle, much like a modern-day human’s. Its age was ballparked at 3 million years, and its size suggested that the being it belonged to stood only a few feet tall. This could mean hominins were bipedal before big brains entered the picture.

All walking aside, what kind of hominin was this? An early Homo species—or something else?

Found Family

The plot thickened during the team’s next dig at Hadar in 1974, which produced three hominin jaws and then, miraculously, Lucy.

Lucy was so special because she was so intact: hundreds of bones and parts of bones that made up some 40 percent of a skeleton. Her large pelvic opening identified her as female, and the shape of her pelvis and legs confirmed that she walked upright. She was about 3.5 feet tall and at least 3 million years old (now dated at nearly 3.18 million), with a small brain and a jaw notably smaller than the others found there. Because of this and other discrepancies between Lucy and those jaws, Johanson guessed that she belonged to one previously unknown species, while the jaws belonged to another. 

But further findings would cause him to change his tune. One was the 1975 discovery of an entire group of hominin skeletons, nicknamed the “First Family,” in Locality 333. “Fossils seemed to be cascading, almost as from a fountain, down the hillside,” Johanson wrote. “A near-frenzy seized us as we scrambled madly to pick them up.” Another was the discovery of fossils in Laetoli, Tanzania, by a team led by Mary Leakey not long after that.

Determining the scientific relationship between all these fossils consumed Johanson and his collaborator Tim White in the summer of 1977. Though Lucy proved especially baffling due to her small teeth, the paleoanthropologists eventually attributed the anomaly to sexual dimorphism: differences in appearance between males and females of one species. At roughly 3.5 feet tall and likely tipping the scales at around 60 pounds, Lucy was the most diminutive adult female in the whole collection, and her teeth showed it. The largest of the bunch measured 5 feet tall and could have been as heavy as 150 pounds. 

In the end, they concluded that everything from Laetoli and Hadar belonged to a single species that, as Johanson explained, “stood somewhere between apes and humans and appeared to be neither one nor the other.” Their brains were fairly proportional to chimps’ brains, their arms hung a little lower than ours, and their faces were apish. But they ambled along more or less like we do. Johanson and White decided to categorize them in the genus Australopithecus, established by Raymond Dart after his 1924 discovery of a hominin fossil known as the Taung child—also somewhere between ape and human (though Australopithecus loosely translates to “southern ape”). For a species name, they settled on afarensis as a nod to the Afar region.

Lucy in the Rearview

As the oldest and most complete hominin skeleton at the time of her discovery, Lucy became the poster child for Australopithecus afarensis and the unofficial mother of all humans. But her legacy is much more nuanced than that, especially in light of all the fossils excavated in the decades after hers was. 

For one thing, we now know that A. afarensis wasn’t the origin point of bipedalism: Evidence suggests that other hominins—including the 4.4-million-year-old Ardipithecus ramidus, the 6-million-year-old Orrorin tugenensis, and maybe even the 6-to-7-million-year-old Sahelanthropus tchadensis—walked upright long before Lucy lived (though they likely did spend time in trees). This reinforces that bipedalism wasn’t a product of brain enlargement, and it may have predated tool use, too: The earliest tools we’ve found so far are only 3.3 million years old.

Why hominins began walking erect remains a subject of debate. According to one hypothesis, it could have arisen from males’ need to carry food to their childrearing mates. Others believe shrinking forests meant more time traversing grasslands, which was more energy-efficient on two feet than four. Still others think hominins actually became bipedal in order to better navigate life in trees.

Another of Lucy’s ambiguities is how she’s related to us. Other hominins that lived around A. afarensis’s time have since been uncovered, from fellow Australopithecus species like A. anamensis and A. deyiremeda to Kenyanthropus platyops (though it has been suggested that the solitary fossil found in that last species is just another afarensis relic). It’s commonly thought that Australopithecus begot Homo, whose earliest fossil to date—part of a jaw found in the Afar region in 2013—is between 2.75 and 2.8 million years old. Lucy’s species prevails as a popular possibility for Homo’s direct ancestor.

“We have now found afarensis in Tanzania, Chad, Kenya and Ethiopia, and we know Lucy and her kin must have lived in these parts of Africa for close to a million years. That antiquity and extensive geographical spread convince me that it is the most likely candidate to have given rise to the many species of the Homo genus and ultimately to our own species, Homo sapiens,” paleoanthropologist Zeresenay Alemseged told The Guardian in June 2024. That said, it’s far from a certainty.

But Lucy’s influence transcends genealogy: She also ignited an unparalleled level of public interest in paleoanthropology. Back in the ’70s, when Johanson told a Paris customs agent that the “funny little parcels” in his suitcase were fossils from Ethiopia, the man lit up. “You mean Lucy?” he said. “A large crowd gathered and watched as Lucy’s bones were displayed, one by one, on the Customs counter,” Johanson recounted. “I got my first inkling of the enormous pull that Lucy would generate from then on.” Naturally, this pull was even stronger within the scientific community.

“One of the major impacts of Lucy’s discovery was that it encouraged so many scientists to go out and survey and explore for more fossils like Lucy,” paleoanthropologist Yohannes Haile-Selassie said at a 50th-anniversary symposium earlier this year. Lucy wasn’t the end of our hunt for humankind’s origin—she was just the beginning.

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