In 1974, scientists working in Ethiopia uncovered an extraordinary female skeleton, whom they called Lucy. She was 3.2 million years old, and belonged to a new species of hominid now known as Australopithecus afarensis. Her brain was small and chimp-sized, but her hips and legs that were clearly built for upright walking—a unique blend of features which revealed that our ancestors evolved a two-legged gait before their brains became big.

Lucy has since become a household name, and it’s easy to forget that she was more than just an avatar of human evolution. She was also a person. Back when her now-famous skeleton was still wrapped by flesh and skin, she was walking around Africa. She ate, drank, and socialized. She climbed trees. And that, if John Kappelman from the University of Texas at Austin is right, is how she died.

Who knows exactly what happened? Maybe she mistimed a jump. Maybe a dry branch gave way beneath her. Maybe she was distracted by a bird. Maybe she was pushed. Whatever the case, Kappelman thinks that Lucy fell—from the tree, to her death, and into history.

He met Lucy in 2008, when she went on tour in the US. Kappelman persuaded the Ethiopian government to send her bones on a brief detour to Austin, so he could put them in a medical CT scanner. Such devices were around when Lucy was first discovered, but they were still crude. Kappelman, however, had access to a high-resolution, state-of-the-art machine. “We had Lucy here for 10 days and we scanned every last bit of bone in her entire skeleton,” he says. “We’ve been working on those scans ever since.”

Along the way, he noticed a set of severe and unusual fractures on Lucy’s right humerus—the long bone of her upper arm. They extended over four different parts of the bone’s head—the bit that connects to the shoulder. After scouring through old papers, Kappelman realized that these kinds of breaks are typically caused by long falls. People instinctively reach out with their hands; when they hit the ground, the impact drives the head of the humerus into the shoulder and shatters it. In trying to break their falls, they break their arms—and in a very distinctive way.

Orthopedic surgeon Steven Pearce confirmed as much. Last December, Kappelman handed him a 3D-printed model of Lucy’s arm, scaled up to human size and with no further information. He quickly identified it as a “four-part proximal humerus fracture”—the common result of falling from a great height. “He said: We see this all the time. What’s the next question?” recalls Kappelman.

Kappelman worked through print-outs of Lucy’s entire skeleton, and eventually the bones themselves while visiting Ethiopia. He found many more breaks, all consistent with a long fall.

The nature of the breaks suggests that Lucy sustained them while she was still alive. If the bones had fractured after her death, say because of floods of scavengers, the separate pieces would likely have split apart and deposited slivers of bone into the surrounding soil. Instead, many of Lucy’s fractures are greenstick ones where the broken bones are still partly connected, and little bone slivers are still stuck to the site of the breaks.

So she was alive—but not for long. The breaks were severe, and with no evidence of healing around them. Whatever caused them also ended Lucy. “The best scenario we can come up with is a fall from a considerable height,” says Kappelman. “That’s also the conclusion of the nine orthopedic surgeons who’ve seen this.”

Here’s their best guess about Lucy’s last moments. She fell, feet first and arms outstretched. The impact broke both of her legs and twisted her body to the right. Her knees hit the ground, both breaking. Her right hip landed—more fractures. When her arms hit, they broke too, the right more seriously than the left. The right shoulder blade pushed her collar bone into her first rib, breaking them both. The final collision between her torso and the ground added more fractures to her hip, ribs, vertebrae, skull, and jaw. Body broken and organs presumably damaged, she would quickly have died.

Some of these injuries had been observed before, but they’d always been regarded as postmortem breaks. Even Kappelman thought so. “I’ve taught this skeleton for 30 years but I hadn’t looked at it in the kind of detail that I did when we started to do these CT scans,” he says. “There are only a few causes of death that are actually preserved in a bone, so in the most part, when we look at a fossil, there’s no evidence for how it died. It’s so rarely the case that we never ask the question.”

But the reconstruction is still hypothetical, say Ericka Labbé and colleagues from the University of Pretoria. Last year, they suggested that hominids of a related species, Australopithecus sediba, also fell to their deaths in a South African cave. But they think that Kappelman’s evidence, as presented in his paper, doesn’t rule out the possibility that Lucy’s bones broke after she died. Such breaks are common when bones fossilize: their organic parts decay away, they become brittle, they get buried by heavy sediments, and they fracture.   

“We invite the authors to engage in a collaborative research project with us, the outcome of which will assist in more strongly interpreting possible fatal injuries of early hominins,” said Labbé in a statement.

Nancy Lovell, a bioarchaeologist at the University of Alberta says that Kappelman’s scenario isn’t implausible, “although it’s bound to be highly controversial.” She adds that falls from a height lead to several classic breaks—the heel bone is crushed; the base of the skull fractures in a ring—but unfortunately, the relevant parts of Lucy’s skeleton have never been found.

There’s also the matter of where she fell from. A tree seems most likely. Her joints and curved fingers suggest that while she clearly walked on the ground, she also spent time among branches. Given her small stature—at 1.1 meters, she was shorter than many chimps—she may have nested in trees at night to avoid predators. Indeed, chimps build nests between 8 and 23 meters above the ground, and they forage even higher. They’ve been known to fall, sometimes to their deaths. Perhaps Lucy did too.

“She may have gone up and down every day her life,” speculates Kappelman. “And it may have been the case that the adaptations for bipedality actually compromised her ability to move safely in the trees, predisposing her to falls.”

“We do have skeletal evidence of trauma resulting from falls in wild-living apes, but this evidence is from animals that survived the trauma,” says Lovell. “If they had died of their injuries, the body was almost certainly not preserved in the wild. So this skeleton of Lucy is all the more noteworthy because it appears to show that she died of her injuries, and her body was fortuitously preserved more or less where she fell—all in all, a series of rare events.”