After 50 Years, Scientists Still Love Lucy

In 1974, researchers unearthed fossil AL 288-1, more commonly known as “Lucy”, in a 3.2-million-year-old deposit in the Hadar region of Ethiopia. In the fifty years since this monumental discovery, paleoanthropologists around the world have spent countless hours analyzing one the most complete fossil hominins ever discovered. This world-famous fossil has also influenced the careers of several of the renowned paleoanthropologists at the National Museum of Natural History.

Rick Potts, the director of the museum’s Human Origins Program, was just starting his career in paleoanthropology when Lucy was discovered, and has since helped contribute to our current understanding of the fossil. Paleoanthropologist Briana Pobiner remembers first learning about the fossil in an introductory course and how the research team named her after the Beatles’ song “Lucy in the Sky with Diamonds.” And researcher Ryan McRae remembers learning about Lucy in the early 2010s after even more hominin fossils were collected and named that helped put Lucy in context. This included the discovery of Ardipithecus ramidus in 1994, another relatively complete fossil skeleton also found in Ethiopia that predates Lucy by about one million years.

Just as hominins evolved over time, so has our understanding of Lucy and where she fits in the tangled tree of human evolution. Over the last half-century, Lucy has taught us about her own species, Australopithecus afarensis, and related species of australopiths and other hominins. Her skeleton has become a critical part of paleoanthropology and has shaped how we study ancient hominins. Here’s just a few things we’ve learned about Lucy.

Lucy’s environment

While Lucy is the most complete Australopithecus afarensis fossil, she’s not the only representative we have of her species. Other A. afarensis fossils have been found, which has allowed scientists to ask bigger questions about the kinds of environments in which these groups of australopiths lived.

“There are not only multiple individuals of Lucy’s species from the Hadar region — there are also animal fossils, and even other kinds of evidence like fossil pollen,” Pobiner said. “These finds led to questions about paleoenvironments and what Lucy’s world was like."

Research generally shows that Lucy and other members of her species lived in a grassy woodland environment. This type of environment, combined with ancient rainfall patterns, would have given rise to a landscape with lots of large trees. This aligns with Lucy’s mosaic of adaptations that allowed her to both walk on two legs and use her long, strong arms and fingers to climb trees.

Lucy’s species

In addition to reconstructing Lucy’s environment, studying A. afarensis fossils helps scientists understand the physical characteristics of this species and how certain traits differ between male and female individuals. The difference in how males and females look is called sexual dimorphism. Having multiple individuals represented in the fossil record can help scientists characterize sexual dimorphism and understand how certain traits show up across a population.

“Lucy’s greatest importance is in the context of the Hadar site as a whole. Lucy has the most complete skeleton from that site, but we have such an amazing range of preservation of many different individuals and all parts of the body,” McRae said. “So having this partially complete skeleton allows you to look at an ancient species in terms of the population context, which you almost never get to do.”

Since the discovery of Lucy and other individuals from the Hadar site, scientists have described sexual dimorphism in A. afarensis, particularly in body size. Lucy stood about 3 feet, 5 inches tall, on the smaller end of the average height for females of her species. Males are estimated to be about 4 feet, 11 inches tall.

Lucy’s adaptations

Because Lucy is the most complete skeleton of A. afarensis ever found, researchers have been able to learn from her unique blend of traits that illustrate how bipedalism and other hominin traits may have evolved over time.

“We have all the indications of Lucy being bipedal and walking on two legs, but in a slightly weird way, different than we would think based on modern humans,” McRae said. “At the same time, she has a braincase and face that looks relatively more ancient than what we would expect for something walking on two legs. So having a complete skeleton allows you to really think about the overall picture of how these traits develop relative to each other.”

Researchers were perplexed by Lucy’s array of adaptations for years. Her skeleton shows signs of upright bipedalism but retains long, curved fingers that would be appropriate for a life in the trees. These traits caused tension within the paleoanthropology community, with scientists taking sides and trying to find evidence to support either a mainly arboreal or terrestrial lifestyle. Eventually, they came to the general consensus we have today of a more flexible lifestyle in which Lucy might have been found in trees or on the ground depending on the environment.

“Now we see that there are clearly signals of both,” Potts said. “As paleoanthropologists, that gets us thinking outside the box and thinking about early hominins on their own terms.”

Lucy’s contributions to paleoanthropology

Lucy’s species is one of the most well-represented hominins in the fossil record, with dozens of individuals represented from across different landscapes and time periods. A. afarensis’s hypodigm, or group of fossils that belong to the species, is so large that researchers use it as a comparison when trying to figure out which fossils belong to which species, according to McRae.

“Because A. afarensis is actually one of the species that we have the best fossil record for as a whole, we’re able to say a lot more about it,” he said. “It’s sort of the benchmark that paleoanthropologists relate new species to in terms of the hypodigm.”

“It’s important to understand that [Lucy and her] relatives represent experiments in being human." 

— Rick Potts, director of the museum’s Human Origins Program

With so many individuals represented in the fossil record, we have a good understanding of the variation between A. afarensis individuals. Every species has some variation — no two Homo sapiens are totally alike in every way — so understanding the variation within a species can help researchers categorize a fossil as a member of one species or another based on the amount of variation compared to the rest of the group.

This can lead to disagreements about whether a fossil belongs to a previously described species or a new one. But having Lucy and other members of A. afarensis helps scientists understand where variations turn into adaptations that define a new species.

Lucy’s next 50 years

While the fossils paleoanthropologists study are millions of years old, our understanding of the species that came before us is constantly changing with new discoveries and new advances in science. New perspectives in the field lead to researchers asking new questions about old fossils, which leads to a better understanding of the fossils we already have and those we have yet to find. And there’s still more to learn from Lucy even fifty years after she was first unearthed in Ethiopia.

Potts is hopeful that the next fifty years of paleoanthropological discoveries will include more trial and error of different hypotheses and looking at each species in its own right, not just because they might be our ancestors. He said that even if we went back millions of years ago to study these hominins, we might not even recognize what we’re looking at if we’re looking solely for evidence of ourselves in these species.

“It’s important to understand that those relatives represent experiments in being human,” Potts said. “Some of them may have passed on their traits to the genus Homo and eventually to Homo sapiens, but that doesn’t necessarily mean that the species we’re looking at is, in fact, a direct ancestor of ours.”

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Emily Driehaus | | READ MORE

Emily Driehaus is a Science Writing Intern with the Smithsonian's National Museum of Natural History. She holds a master's degree in science journalism from New York University and has worked as a journalist and science writer covering everything from microbiology and climate change to particle physics and quantum computing. Her writing has been published in Sierra Magazine, Symmetry Magazine, VICE News, and other outlets. You can find more of her work here.