Dr. Donald Johanson woke up on the morning of November 24, 1974, feeling lucky. The paleoanthropologist—then a professor at Case Western Reserve University in Cleveland—was several weeks into his third expedition to Hadar, Ethiopia, a site that had proven to be a treasure trove of early fossil remains. His international field team had already found leg bones and several jaws that were among the oldest examples of hominids—the family of bipedal primates that includes humans and their ancestors—and Johanson was convinced that an even bigger discovery was in the offing. When an American graduate student named Tom Gray announced he was leaving to scout out a nearby fossil site, Johanson had a hunch he should tag along. “I felt a strong subconscious urge to go with Tom,” he later wrote. “I felt it was one of those days…when something terrific might happen.” Ignoring the already scorching heat and the mountain of paperwork on his worktable, Johanson hopped in a Land Rover with Gray and made the four-mile journey to a gully on an ancient, dried out lakebed. Before he left, he made a brief note in his journal: “To Locality 162 with Gray in AM. Feel good.”
Johanson and Gray’s search turned up very little at first. The pair found a few animal bones and teeth, but nothing extraordinary. After a few hours of scouring the sunbaked ground, they decided to take a detour through a nearby gully for one last look. There, Johanson spotted what he instantly recognized as a piece of hominid elbow bone protruding from the dirt. When he and Gray bent down to examine it, they saw that it rested next to other pieces of thighbone, vertebrae and ribs. All appeared to belong to the same skeleton. “We were just astounded,” Johanson later told the New York Times. “You just don’t expect to find this much of a single individual.” Johanson and Gray raced to tell their colleagues. As they drove up to their camp, Gray laid on the horn and yelled out, “We’ve got it! Oh, Jesus, we’ve got it. We’ve got the whole thing!”
While hunting for fossils in Ethiopia’s Afar Triangle on November 24, 1974, paleoanthropologist Donald Johanson and graduate student Tom Gray stumbled upon the partial remains of a previously unknown species of ape-like hominid. Nicknamed “Lucy,” the mysterious skeleton was eventually classified as a 3.2 million-year-old “Australopithecus afarensis”—one of humankind’s earliest ancestors. The headline-grabbing find filled in crucial gaps in the human family tree, but it also shook up ideas about early human evolution and upright walking. Forty years later, learn the story behind the fossil that permanently changed scientists’ understanding of human origins.
Equally remarkable was how old she was. While the scientists couldn’t date the fossils directly, the age of the geological strata in the Hadar Basin indicated the Lucy skeleton was likely more than three million years old—far more ancient than other hominids. Once Lucy’s skeleton had been transported to the United States for further study, geologists used potassium-argon dating and other methods to fix the age of the basalt layer surrounding the discovery site at around 3.6 million years old. That number was later amended to 3.2 million years old using a more sophisticated radiometric dating process known as argon-argon dating.
Johanson’s first impulse was to label Lucy as part of the genus Australopithecus, a family of ape-like hominids that thrived between 2 and 4 million years ago. But when he took a closer look, he saw that many of her features were significantly more primitive than other Australopithecine specimens. Starting in 1976, Johanson and U.C. Berkeley anthropologist Tim White studied Lucy’s skeleton even further in an effort to place her in humankind’s family tree. The duo compared Lucy to a so-called “First Family” of some 13 other skeletal remains found at Hadar as well as to a collection of hominid footprints excavated by famed anthropologist Mary Leakey in Laetoli, Tanzania. Finally, in 1978, they released a groundbreaking paper classifying Lucy, the other Hadar fossils and the Laetoli footprints as all belonging to a brand new species of early hominid human ancestors. They called them “Australopithecus afarensis,” after the Afar Triangle in which Lucy was found.
Johanson and White’s bombshell promptly encountered backlash from the anthropological community. Many held that Australopithecus afarensis was not a discrete species, and still others—most notably the Kenyan paleoanthropologist Richard Leakey—balked at the assertion that fossils like Lucy were the direct ancestors of modern humans. The case for Australopithecus afarensis was strengthened in the early 1990s, however, when further research at Hadar yielded a wealth of other Lucy-like fossils including near-complete skulls of both male and female specimens. All told, Johanson and other researchers eventually collected fossils belonging to several hundred different Australopithecus afarensis individuals. These finds have helped bring Lucy and her kind into even sharper relief. Studies of afarensis shoulder bones have shown that Lucy most likely spent as much time climbing trees as she did walking upright on the ground, and other evidence has shown that she may have been a social animal that lived in small family units.
In the years since Lucy was lifted from her 3.2-million-year-old grave, anthropologists have gone on to find older and even more complete fossil remains of early human ancestors. In 2000, scientists in Ethiopia unearthed the remains of a 3.3 million year old Australopithecus afarensis baby dubbed “Selam.” The child was 100,000 years Lucy’s senior, but it’s now often known as “Lucy’s Baby.” Perhaps even more spectacular was “Ardi,” a 4.4 million year old Ardipithecus ramidus that displaced Lucy as the earliest known skeleton of a human ancestor. News of “Ardi” first came to light in 1994, but since then, scientists have found evidence of even older hominids dating back as far as 7 million years ago.
Despite these more recent breakthroughs, Lucy still stands as perhaps the most famous hominid fossil discovery ever made. Casts of her skeleton sit in museums around the world, and hundreds of thousands of people flocked to a traveling exhibition of the original Lucy fossils in the 2000s. In a 2009 interview with Time, Johanson speculated that Lucy’s enduring celebrity stemmed from the way she helped fill in the blanks in our understanding of early humans. “She showed us conclusively that upright walking and bipedalism preceded all of the other changes we’d normally consider being human…” he said. “She gave us a glimpse of what older ancestors would look like.”
As mentioned in the previous paragraph, Lucy was allocated to the species, Australopithecus afarensis, meaning “African southern ape from the Afar region.” However, Lucy was not the first A. afarensis discovery. An articulated knee joint dating to 3.4 million
years ago (Ma) was discovered a year earlier in 1973, but it was not properly identified as A. afarensis until 1979. Still, Lucy’s discovery eclipsed nearly all earlier findings because of the extraordinary completeness of Lucy’s skeleton, making her one of the most important paleoanthropological findings of our time. Roughly 40% of Lucy’s skeleton is accounted for (hands and feet excluded), including cranial material such as fragments
of the cranial vault, face, and jaw. Postcranial material includes parts of the shoulder, spine, and pelvis. Much of the limbs bones are also represented (upper arm and forearm fragments, a carpal and finger bone, a partial
tibia and nearly complete femur).
The preservation of so much of Lucy’s skeleton has allowed researchers to study a number of aspects of her anatomy, about how she moved in her environment (locomotion), what she ate (diet), and even to
hypothesize about how she is related to modern humans.
Lucy’s evolutionary relationship to modern humans was one of the first questions asked by scientists after the “Lucy” discovery. The process of determining relatedness among
organisms is called systematics. Unfortunately, we can’t travel back in time to answer this question. However, in one type of systematics called cladistics, we can understand the evolutionary relationships among organisms by grouping them together based on shared characters (traits) (See the eFossils lesson “Evolution: From the Beginning” for more information). Specifically, cladistics is concerned with features that are novel and unique,termed derived features, to a particular subset of animals within a larger group. For example, among mammals, primates have nails. Since, most other mammals have claws, nails are a derived primate feature. In contrast, characters that everyone in the larger group has are termed primitive characters. For example, primates have hair, but so do all mammals. In this case, hair is a primitive feature that primates share with all mammals.All organisms that share a derived character belong to a clade.
Lucy has two ages: one that refers to how old she was when she died, her biological age, and the other that refers to how long ago she lived, her geological age.
Lucy was an adult when she died. Scientists are able to determine this age because Lucy had fully erupted wisdom teeth (or third molars) and her bones appear fully fused. Bones form in separate pieces and fuse
(connect) together at different times in life, just as teeth erupt at different ages as an animal grows. By the age of 35, most humans have fully erupted third molars and completely fused bones. Lucy’s geologic age dates to 3.2 Ma3. After Lucy died, her bones settled into dirt and rocks, called sediments.
She then was buried by many more layers of
sediments. The weight of all these sediments crushed some of her bones. After a long time, the calcium in her bone was replaced with minerals from the surrounding soils. This process is called mineralization. It turns the bone into rock which help preserve it for a long time. Scientists can determine when Lucy lived by testing chemicals, called Potassium-Argon and Argon-Argon, in layers of volcanic ash above and below the rock layer where Lucy was found. Lucy was found in sandstone sediments associated with a paleo-stream. In this context, it is possible that a stream carried Lucy’s body some distance away from where she died4
Where did Lucy live?
Lucy probably lived in a mixed environment from dense wooded areas to open grassland areas, characterized by both wet and dry conditions. Thus, Lucy was probably able to tolerate the living conditions of a broad range of habitats. There is no evidence that Lucy or other members of her species preferred one habitat over another
What did Lucy eat?
Lucy probably ate a mix of foods, including ripe fruits, nuts, and tubers from both the forest and savanna. Incisor teeth are typically used to prepare the food for mastication (think about biting off a piece of an apple), and molar teeth are used to masticate, or chew, the food into a small pulp that can be swallowed. Compared to chimpanzees, Lucy had relatively smaller incisor teeth, but larger molar teeth, suggesting that she did little to dentally prepare her food, and spent more time intensively chewing or breaking down the food.
Additionally, the enamel or hard outer shell of the tooth, and the body of the mandible
itself, were relatively thicker in Lucy than chimpanzees, affording greater strength for the mastication of tough or hard-object foods. Foods that require a lot of chewing include nuts, seeds, and underground storage organs (root vegetables). However, A. afarensis incisors also show patterns of wear consistent with stripping leaves, and the canines show patterns of wear consistent with puncturing or crushing foods. Thus, Lucy probably also ate ripe fruits when they were seasonally available.
What did Lucy look like?
Lucy was a small-bodied female that probably stood about 3”6” (107cm)8
tall and weighed roughly 60 pounds (27.3 kg)9. Scientists can tell that Lucy is female because the anatomy of her pelvis generally resembles that of female modern humans.
In addition, Lucy’s body size overall, as well as those of other female A. afarensis, is smaller than the body sizes of male A. afarensis specimens. A difference in body size between males and females of the same species is called sexual dimorphism, meaning two (“di”) forms (“morph”) between sexes.Lucy’s face was chimpanzee-like. Below her eyes, her faceprojected forward beyond the plane of the eyes, a character trait known as prognathism. Features that Lucy shares with chimpanzees are called retained primitive features, meaning that these features were present in the ape-like species from which Lucy’s species evolved, and that Lucy’s species, A. afarensis, kept these features even after the species diverged from that last common ancestor.
How big was Lucy’s brain?
Fossil remains of Lucy’s braincase are fragmentary, limiting the reconstruction of her brain size. However, brain size estimates from other members of her species suggest that Lucy’s brain was probably about the size of a modern chimpanzee’s (range between 387 – 550 cc; average 446 cc). Although it might appear as though these australopiths had small brains, it must also be remembered that they were smaller-bodied than living humans. In fact, when her brain size compared relative to her body size, her brain would actually be considered larger than expected for a living ape of that body size. Importantly, Lucy’s relatively small brain size (compared to humans) in combination with her bipedal adaptations of the lower limb, reveal that bipedalism evolved before large brains.
How did Lucy move?
Lucy was clearly bipedal, although she may have continued to locomote through trees (i.e., arboreal locomotion) with some ease. Scientists can deduce this information from her skeleton, which is a combination of derived human-like features and retained primitive chimpanzee-like features. Each section below discusses aspects of Lucy’s anatomy that help us determine her mode of locomotion. Limb proportions: An animal’s limb proportions can provide clues as to what mode of locomotion an animal utilizes on a regular basis. A ratio of limb proportions is calculated by dividing the forelimb length (humerus length + radius length) by the length of the hindlimb (femur length + tibia length). This ratio is called an intermembral index (“inter” means “between”, “membral” means “limb”).
Since the evolutionary trend in hominins is toward relatively longer hindlimbs than
forelimbs, as in modern humans, Lucy’s skeleton shows that arm length reduced before thigh elongation. Functionally, Lucy probably relied on her hindlimbs for moving bipedally and on her forelimbs for climbing. Scapula: Some of Lucy’s primitive features, such as the orientation of her shoulder, suggestthat she might have spent some time in the trees (arboreal). The scapula (shoulder blade) articulates with the humerus (upper arm bone) at the scapula’s glenoid fossa, a small circular or oval depression located on the scapular head. A cranially (up, toward the head) oriented glenoid fossa enhances an animal’s ability to climb or use forelimb-dominated activities where the arms are held above the head. Like chimpanzees, and unlike humans, the A. afarensis glenoid fossa faced cranially, suggesting Lucy probably used above-head arm postures, consistent with the idea that she may have climbed trees.
Key Facts About Lucy
1. Donald Johanson discovered Lucy in 1974 in a maze of ravines in the Afar region
of Ethiopia, near Hadar. She was named after the Beatles’ song Lucy in the Sky
with Diamonds, which was played during a celebration of the discovery. The
Ethiopian people refer to her as “Dinkenesh,” an Amharic language term meaning
“You are Marvelous.”
2. At 3.2 million years old and with 40 percent of her skeleton preserved, Lucy is the
oldest, most complete and best preserved skeleton of any erect-walking human
ancestor that has ever been found and completely excavated. Lucy is quite small,
at about 3.5 feet tall and may have weighed about 60 lbs.
3. The discovery of Lucy yielded an entirely new species of human ancestor, known
as Australopithecus afarensis, or “southern ape of Afar,” after the region of
Ethiopia where the bones were found.
5. The fossil known as Lucy was determined to be female based on several traits.
o Lucy’s small size compared to other representatives of the same species.
o Lucy’s small size is seen as an expression of “sexual dimorphism.” This
terminology refers to the difference in shape between individuals of
different sex in the same species. For example, in mammals, the male is
larger than the female.
o The first complete male afarensis skull was discovered in 1994, less than
ten kilometers from the site of Lucy’s discovery. An analysis of the skull
indicated that afarensis males were twice the weight of females.
o The shape of her pelvis compared to the pelvis of the larger individuals.
6. Learning to walk upright, as scientists believe Lucy did, was risky; it eliminates
tree-tops as a refuge from predators and results in bone and joint problems while
requiring the same amount of energy. Standing also makes it much easier to be
seen by predators. There are multiple theories that attempt to explain why animals
like Lucy began to walk upright.
7. Lucy retained ancestral traits, including the ability to climb trees with much more
ease than we do. This would have allowed her to seek refuge from predators in
8. Earlier theories of evolution suggested that human-like intelligence evolved first
and upright posture (bipedalism) followed; the existence of Australopithecus
refutes this theory.
9. The study of Australopithecine teeth suggests that Lucy’s diet consisted of fruits,
nuts and seeds. We also surmise that they would have scavenged animal carcasses
and taken advantage of birds’ eggs and termites’ nests.