It was already pretty hot by the time Donald Johanson and his graduate student, Tom Gray, arrived at the site at Hadar, Ethiopia, on the morning of November 24, 1974. The two had initially set out to map the location but decided to have a look around for any signs of fossils while they were there. Unfortunately, there were very few fossils visible on the surface at the time, but they did manage to find some fragments belonging to antelopes, gazelles, and even a bit of a monkey. Not exactly the most auspicious of finds for a site that was known to have sediments that are over 3 million years old.

As the baking sun reached its zenith, the two researchers started back to the car, but they decided to go via a different route along a gully. It was at this point that Johanson happened to look over his shoulder and something caught his eye. Lying on a slope was a small piece of bone that appeared to be the right proximal ulna (forearm) of some sort of animal – probably a monkey. However, as he turned the piece over in his hand, Johanson realized he was looking at something different – it appeared to belong to some sort of hominid.

While examining the rest of the slope, Johanson and Gray then found a piece of skull bone, a femur, a pelvis, some ribs, and a lower jaw complete with some teeth.

These bones were tiny, but over the next few weeks of further excavation, Johanson, Gray, and colleagues discovered several hundred bone fragments at the site now known as Afar Locality 288. They carefully logged the exact location for each piece and then took them back to camp for further analysis. Eventually, the team had collected around 40 percent of a single skeleton belonging to a previously unknown hominid species.

At the time, Johanson and Gray knew they had something special on their hands, but they were not aware of just how significant this find was and what it would mean for our understanding of human ancestry.

It has now been 50 years since Lucy’s skeleton was found on that Ethiopian slope, and over the decades she has become an iconic figure in the story of human evolution.

Lucy on a slope with gravel 

“Lucy” may not sound like a name you’d give an important scientific specimen, but it is pretty memorable, as is the story of how it came about. 

She began to emerge as a personality as well as an important scientific discovery.

Donald Johanson

As Johanson told IFLScience, while the excavation team relaxed in their camp on that night in November 1974, he and his then girlfriend, Pamela Alderman, were discussing the potential sex of the mysterious specimen when The Beatles’ 1967 hit Lucy in the Sky with Diamonds came on the radio. As Johanson was convinced the bones belonged to a female individual, they decided to nickname her Lucy.

The technical name of the hominid species Lucy belonged to – for which she was the first known example – was Australopithecus afarensis, but that was neither known at the time, nor is it so easy to remember.

“Once that [name] was uttered,” Johanson told IFLScience, “it stuck. From then on, everyone just started saying things like ‘Are we going to go back to the Lucy site? Do you think we’ll find more of Lucy’s skull? How old do you think Lucy was when she died? Etc, etc.’”

“So she began to emerge as a personality as well as an important scientific discovery.”

And that’s a significant component of Lucy’s legacy.

“[S]he’s become sort of the benchmark… I think that even more than [being just a skeleton], people recognize this discovery as an individual.”

Lucy and Australopithecus afarensis

Australopithecus afarensis is a member of the australopithecine group, early hominins (humans and their close and now extinct relatives) that lived in Africa around 4.1 to 1.4 million years ago. Prior to Lucy’s discovery in 1974, palaeoanthropologists were aware of only one other member of this group – Australopithecus africanus (meaning “southern ape of Africa”) – which had been discovered back in 1924. But, at this time, fossil discoveries were extremely limited, so not much was known about these ancient hominids.

The relatively complete nature of Lucy’s remains, however, provided an unprecedented understanding of the species. Importantly, Lucy’s skeleton indicated that these early hominids were bipedal, walking upright on two legs, like modern humans. For instance, Lucy’s distal femur (the lower part of her thigh bone that forms the top part of the knee joint) has several features that are unique to bipedality. This includes the angle of its shaft relative to the condyles (the rounded part of the joint), which allowed Lucy to balance on each leg, one after the other, as she walked.

If we had developed big brains first and were still quadrupedal, and we were out there looking over the tall grass, you would announce that you were on the menu.

Donald Johanson

These condyles are also quite large, suggesting they could handle the increased weight that comes with this type of locomotion. Other markers of bipedality include the shape of her pelvis, which is adapted for upright balance; and significantly, her talus – the bone in the ankle that connects foot to leg – shows signs of a big toe that would have been used for balance and shock absorption, rather than the manipulative abilities we see in monkeys and apes.

But despite the significance of this evidence, not everyone was convinced of Lucy’s importance. As with so many instances in the history of science, some members of the wider scientific community took some time to accept that they were indeed dealing with not only a new species of hominid, but also one that walked upright.

“There was a lot of opposition as to the meaning of the diversity in the specimens,” Johanson explained. Some researchers believed that, rather than walking upright like a human, Lucy was merely “the ape that stood up,” meaning she walked with bent hips and bent knees.

“That’s not a very efficient way to walk,” Johanson added. “I mean, you’re expending so much energy; you fatigue extremely quickly.”

In terms of human evolution, Lucy’s ability to walk on two legs suggested that humans (and their relatives) evolved bipedality before their brains increased in size. This was an important realization: Lucy had the anatomy for walking on two legs, but the brain case of her skull was “very small”. As Johanson explained, “The endocranial volume was sort of like what you would typically see in a chimpanzee.”

“This meant the long-standing argument about ‘did we stand up first and then get big brains so that we could, you know, leave the forest trees or the forest, and then make a living out on the Savannah’ was settled,” he added.

“If we had developed big brains first and were still quadrupedal, and we were out there looking over the tall grass, you would announce that you were on the menu. So in terms of natural selection, you’d be gone.”

How do we know Lucy was female and how old was she?

Okay, so Lucy’s skeleton can tell us a lot about how these hominids moved, but how do we know she was female and not, as Johanson said, “Lucifer”, a male? Well, according to Johanson, it was obvious the specimen was female from the moment he found the fossil fragments, and this related to their size.

Although the difference between modern male and female humans is very limited, apes and other ancient human ancestors had high levels of what is called “sexual dimorphism” – difference in size and shape between male and females. This was also true for Australopithecus afarensis.

“You have sexual dimorphism. Yes, differences in size and all of these early human ancestors had males that were significantly larger [than females], probably because they’re being selected for large size, perhaps for protection of the troop they’re living in, and also warding off predators and so on.”

“And females are being kept small because they have very high energy requirements, you know, nurturing a foetus, giving birth, breastfeeding a child.”

Given how small Lucy’s bones are, it would suggest a female individual. Some may argue that perhaps this means the specimen was just a child, but Lucy’s teeth also show signs of age. Her jawbone has third molars – her wisdom teeth – which have erupted and have begun to wear. This would suggest Lucy was at least a young adult when she died.

At the same time, Lucy’s bones and skull had fused, suggesting she had completed her skeletal development.

What happened to Lucy?

It is currently unclear how Lucy died, but we can infer a few things from her bones. Firstly, there is no indication that she was killed by a predator. If she had been attacked by an animal, you would expect to see marks from teeth or claws on her remains, but she is free of such evidence.

In 2016, a study conducted a CT scan of her bones and suggested that Lucy had fractures in her shoulder joint and arm that are consistent with those experienced by someone falling from a height. However, this study’s conclusions remain controversial and have not been accepted by everyone, including Johanson, who believes the fractures could have occurred postmortem.

The future of our (evolutionary) past

Over the last 50 years, Lucy (along with subsequent discoveries) has helped us understand significant aspects of our evolutionary heritage. However, there remain many questions yet to be answered. Johanson would like to think that, in the next 50 years, palaeoanthropologists will be able to address current mysteries related to the palaeoenvironment in which Lucy and other members of her species lived. In particular, this could help explain why some species of ancient hominins died out while others survived.

At the same time, there are still many questions related to the development of human intelligence, and at what point, and under what conditions, did our brains start to grow in size?

“The first tools are well over 2.6 million years old,” Johanson said, “but we don’t see any significant brain expansion until around 2 million years, right? So I think we want to know not just what types of changes were going on but the reason why they happened.”

These are just some of the questions that are being explored at the moment by palaeoanthropologists. Perhaps they will be answered in the near future or maybe it will take longer, but it will be interesting to see whether Lucy plays any role, or whether the findings add to what we know of this enigmatic individual.