Inside a specially constructed safe at the National Museum of Ethiopia in Addis Ababa sit the fragile remains of the world’s most celebrated human ancestor. She was once a hardy survivor in an unforgiving environment, but now her partial skeleton receives round-the-clock protection in a temperature-controlled setting.

In her prime, nearly 3.2 million years ago, this ancient female roamed East Africa’s landscape. Standing a bit over 1 meter tall and weighing no more than about 30 kilograms — slightly taller and lighter than an average adult female bonobo chimp — she was not physically imposing.

But her evolutionary stature and cross-cultural appeal are huge. Today, half a century after the discovery of her partial skeleton, people everywhere know Lucy.

Discovering Lucy ushered in a new way of thinking about human evolution among late-20th century paleoanthropologists. At that time, many viewed human evolution as having proceeded along a straight line, with one ancient Homo species leading directly to the next until the emergence of present-day people.

But Lucy’s blend of humanlike features, such as a curved spine, with apelike traits, including a brain no larger than a chimp’s and long arms, pointed to a more treelike picture of human evolution. In that scheme, myriad species branched off in different directions, some dying out and others leading to the Homo genus and eventually to us.

Lucy’s anatomical potpourri also sparked new questions about how two-legged walking evolved and the origin of humans’ large brains.

Perhaps most importantly, Lucy’s discovery foreshadowed a series of fossil finds that filled in the scientific picture of her species. By 1978, enough evidence had accumulated to establish Lucy as the founding member of a previously unrecognized species, Australopithecus afarensis.

On the 50th anniversary of her partial skeleton’s discovery, Lucy commands much more name recognition than other fossils from humankind’s evolutionary family, known as hominids or, increasingly, hominins. A look back at Lucy’s story reveals how she has remained atop the hominid A list. In this case, geologic good fortune, skilled scientific scrutiny and an inspired musical reference helped to turn an ancient relative into a household name.

Get buried but not too deep

Paleoanthropologist Donald Johanson and graduate student Tom Gray spent the morning of November 24, 1974, mapping and surveying possible fossil-bearing spots in a desolate region of Ethiopia. Walking back to their Land Rover through a gully at a site known as Hadar, Johanson noticed a forearm bone sticking out of the ground. A closer look confirmed that the bone came from a hominid.

Johanson and Gray gingerly removed several more skeletal pieces from loose soil nearby. After two more weeks, the researchers and their colleagues had uncovered several hundred bone fragments — a big haul considering finding one ancient hominid skullcap or partial jaw can require weeks or months of careful excavation.

From those finds, the team pieced together 47 fossil bones to form a small fossil skeleton about 40 percent complete. It was the most complete early hominid skeleton at that time — by a lot (SN: 1/4/75).

Geology had worked in Johanson and Gray’s favor. Lucy’s remains were not found where she died. Flooding had carried her body, probably shortly after death, into a sandy channel where a lake quickly formed. The burial under moist lake sediment kept her fossilized bones in relatively good shape. And the fossils were near enough to the surface that, much later, after the lake had dried up, they began to emerge from eroding, sandy sediment.

Scientists continue to debate how Lucy died (SN: 8/29/16) and whether scavenging by hyenas and other animals, trampling or other factors explain her skeleton’s missing pieces. But what remained popped out just enough from Hadar’s surface to get the fossil party started.

Stay close to fossil comrades

Part one of the geologic good fortune involved Lucy’s skeleton. Part two ushered her species mates into view.

Lucy was found on land that, although not evident at first, preserved bones of many of her contemporaries. Fossils unearthed from 1973 to 1977, including a knee joint that predated Lucy’s discovery but was only later recognized as part of her species, cemented Lucy’s membership in a larger A. afarensis population (SN: 1/20/79). Those finds enabled scientists to distinguish between Lucy’s East African species and a previously identified species of South African hominid in the same genus, Australopithecus africanus.

Other generally accepted hominid species known at the time mostly belonged to the Homo genus — including Homo habilis, Homo erectus and Homo neanderthalensis.

As evidence for A. afarensis grew, Lucy came to symbolize the entire species.

Fossils from several East African sites, some excavated as early as the 1930s, have since been incorporated into A. afarensis. Hadar has yielded about 90 percent of the nearly 600 fossils so far attributed to the species.

Hadar’s geology also gave Lucy a big advantage in the ancient dating game. The three Hadar sediment formations with A. afarensis remains each contain layers of volcanic matter and ash. Measures of the decay of radioactive argon into related forms in that volcanic material provided age estimates for the fossils. The ability to narrow down Lucy’s evolutionary age in this way shortly after her discovery reinforced her status as an especially early hominid — the oldest known at that time — with an exceptionally preserved skeleton.

While Lucy lived an estimated 3.2 million years ago, her species at Hadar and elsewhere existed from about 3.9 million to 3 million years ago, making her a flag bearer for a hominid species that had a 900,000-year run.

To paraphrase an old Beatles song, Lucy topped the hominid hit parade with a little help from her friends.

Names matter

Another Beatles song advanced Lucy’s worldwide fame by providing a catchy, memorable name.

After the initial Hadar discovery, when Johanson and Gray returned to camp for the night with what looked like pieces of a hominid skeleton, they joined the rest of the team in a celebration. A tape recorder played the song “Lucy in the Sky with Diamonds” over and over during the festivities. The tune’s psychedelic lyrics echoed the surreal events of that day. Joyous partyers started calling the newfound fossil Lucy.

With that thoroughly modern moniker, familiar to people around the world, Lucy from the gully in Hadar received a big boost toward fossil stardom.

The origin of Lucy’s nickname was far more raucous and spontaneous than is typical for fossil hominid specimens, which often get named for the place where they were found. Consider the Taung Child, a 3-year-old’s fossil skull uncovered by miners at South Africa’s Taung quarry in 1924. Researchers generally agree that the discovery of the Taung Child — which may have lived anywhere from around 3.7 million to 2 million years ago, depending on age-estimation methods — launched the modern era of fossil hominid studies.

The Taung skull turned researchers’ attention away from Asia and toward Africa as the birthplace of hominids. In 1925, anatomist and anthropologist Raymond Dart assigned the find to Australopithecus africanus, a new species that he considered a direct ancestor of the Homo line.

The position of the ancient child’s skull opening for the spinal cord showed that the head rested directly above the spine, a hallmark of the ability to walk upright. Though the South African skull hinted that early hominids had adopted a two-legged gait before big brains, some researchers suspected that Taung would have developed into a chimplike, knuckle-walking adult.

The Taung Child certainly deserves recognition in this centennial year of its discovery. But the fossilized Hadar female named for a trippy rock song has gained far more public acclaim than the ancient kid named after a quarry.

Lucy goes by other names. Her formal designation, rarely used outside academic journals and scientific meetings, is AL 288-1. And Ethiopians today refer to the remains as Dinknesh, a word that in a regional language means “you are marvelous.” On the world stage, though, the Hadar female answers only to Lucy.

Inspire big evolutionary debates

Lucy would have appreciated the lyrics of another Beatles song that opens with: “I’m looking through you, where did you go? I thought I knew you, what did I know?”

Her partial skeleton revealed enough anatomy to reshape debates about hominid evolution without supplying easy answers. Five decades later, those disputes continue.

At the time of the Hadar find, the fossil discoveries and evolutionary ideas of Louis and Mary Leakey and their son Richard dominated anthropology. Louis Leakey regarded human evolution as having occurred solely within the Homo genus. Probably starting with H. habilis, he argued, one Homo species led to the next without any branching into dead-end lines. South African australopithecines, such as the Taung Child, represented extinct ape species, from his perspective.

Big brains powered the rise of the Homo genus and eventually people today, starting in Africa perhaps 3 million years ago, the Leakeys argued.

Lucy, with a body built for humanlike walking topped by an apelike brain, challenged that idea. Johanson placed Lucy’s kind at the center of a dramatic split in hominid evolution, with A. afarensis evolving in one direction into later australopithecines and in another direction into the Homo genus. That view is still held by Johanson and many others today.

At a minimum, Lucy’s partial skeleton strengthened the argument — until then based on the tiny Taung skull — that a two-legged stride arrived before the emergence of big brains in human evolution.

Lucy’s lower-body design triggered a related dispute. Her spine and legs were adapted for an upright gait, which would reinforce her proposed status as a direct Homo ancestor. But relatively long arms and curved fingers resembled those of a tree-climbing ape. After Lucy’s discovery, researchers debated whether the species divided its time between the trees and the ground, or mainly stayed on the ground despite retaining skeletal traits of tree-climbing ancestors.

Lucy’s preferred mode of getting around remains a hot topic (SN: 10/25/12). Frequent tree climbing, possibly linked to exceptional upper-body strength (SN: 11/30/16), would support a controversial proposal that she fell to her death from high up in a tree. If an efficient two-legged stance kept Lucy grounded, as suggested by another A. afarensis fossil find (SN: 6/21/10), then she probably died from some other cause.

Crucial questions also concern her species’s diet and possible stone tool use (SN: 8/11/10). In 2000 at another Ethiopian site, researchers discovered the nearly complete fossil skeleton of a 3-year-old girl from Lucy’s species, which they named Selam. Later evidence from that site suggests that A. afarensis used stone tools to obtain marrow, meat and fat from animal carcasses. If those findings hold up, then meat eating did not rapidly lead to bigger hominid brains, as many researchers have assumed.

Make the right scientific friends

Lucy attracted big-time researchers from the moment Johanson and Gray started retrieving parts of her skeleton. The evolutionary status of the ancient Hadar hominid and her kind soared thanks to her newfound admirers’ collaborative efforts and publications.

Johanson, Lucy’s first champion, arrived at Hadar in 1972 as part of an international fossil-hunting expedition. His colleagues included three already distinguished researchers, all now deceased: paleoanthropologist Yves Coppens, geologist Jon Kalb and geologist Maurice Taieb, who had discovered the Hadar Formation in 1968 and organized the expedition. The team became immersed in excavating more Hadar fossils, with a first wave of fieldwork running through 1977.

Johanson recruited a young paleoanthropologist who would go on to have a bright future in fossil hunting and analysis, Tim White, to help analyze the growing trove of ancient bones. It was in a 1978 paper that Johanson, White and Coppens identified Lucy and other fossil hominids at Hadar and another East African site, Laetoli, as a new species.

White added a keen eye and voluminous knowledge of bones to the early studies of Lucy and her kind. In 1991, White published Human Osteology, a classic book on how to analyze human skeletons that is still in print. The next year, he published an influential book on how to recognize signs of cannibalism on human bones (SN: 1/2/93). He later directed excavations of a 4.4-million-year-old partial hominid skeleton known as Ardi that also shook up the human family tree (SN: 12/31/09).

Johanson thrived in a role as scientific popularizer. His 1981 book Lucy: The Beginnings of Humankind, coauthored with writer and naturalist Maitland Edey, brought her worldwide attention. In the same year, newscaster Walter Cronkite moderated a nationally televised debate between Richard Leakey and Johanson.

Though fieldwork stopped in 1977 due to an increasingly violent Ethiopian Civil War, in 1981 Johanson met an anthropology graduate student who would direct a second wave of Hadar excavations. William Kimbel started out by analyzing braincase remains of A. afarensis. In the early 1980s, Kimbel worked with Johanson and White to detail why A. afarensis and A. africanus were different species.

Kimbel took charge of a new phase of fieldwork in 1990 as the civil war neared its official end the next year. He raised funds for, organized and directed A. afarensis excavations for the next three decades. During the 1990s, he helped lead a movement to understand different species concepts and their implications for primate evolution.

Lucy’s kind had no better Homo sapiens friend than the paleoanthropologist everyone called Bill. Paleoanthropology suffered an enormous loss in 2022 when Kimbel, who also directed the Institute of Human Origins at Arizona State University from 2009 to 2021, died of abdominal cancer at age 68.

Kimbel, like Lucy’s discoverers, had argued that she is a direct ancestor of the Homo genus, a proposal that remains controversial. To this day, few early Homo fossils exist for comparison with A. afarensis. Kimbel contributed to the analysis of one such find, a roughly 2.8-million-year-old Homo jaw found near Hadar. In his view, traits of that fossil indicate that one branch of Lucy’s species evolved into the first members of the genus Homo, and eventually gave rise to H. sapiens (SN: 3/4/15).

During the televised debate between Johanson and Richard Leakey, Johanson presented a drawing of his proposed hominid family tree. Leakey scrawled a question mark over it. Decades later, Lucy and her Hadar crowd still elude scientific consensus.

But no matter how this pivotal evolutionary issue plays out, Lucy’s trip from a Hadar gully to an Ethiopian museum vault has been eventful for her species and anyone interested in the origins of humankind. Fifty years after stopping a couple of fossil hunters in their tracks, Lucy’s star power shines bright.