Lucy is our most famous relative. She lived in what is now Ethiopia 3.2 million years ago. There, split her time between tree climbing and walking on the ground like us. She was mostly vegetarian and may have used tools to help her get those nuts and plants she likes. We know all of this because she's one of the most complete fossils we've ever found. Despite this, there's still a lot we don't know about her. Including how she died. New research claims to have found the answer: she had a nasty fall out a tree.
Fall out of tree, break bones, die
Lucy was discovered more than forty years ago. So how is it we're only just finding out about the fact she fell to her death? This all stems from the sheer quality of this latest study. It involved carrying out a CT scan on Lucy's remains, allowing the authors to create 3D models of the bones and examine them in more detail than anyone had ever done. Crucially, this also allowed the researchers to examine the inside of the bones.
All of this began to reveal some rather interesting patterns. In particular, many of her limbs had evidence of compression fractures. This is what happens when a lot of force travels through the bones, causing the joints to crash into each other. This can result in tremendous damage. In Lucy, for example, it shattered parts of the joint and sheered off others. She also seems to have broken her feet, hips, ribs, and part of her skull.
Crucially, this was all interpreted as having occurred prior to death. The compression fractures in the arms were consistent with falling from a great height and stretching the arms out in an effort to stop herself from falling. Many of the other injuries also showed evidence of being hinge fractures, which typically only occur whilst an individual is alive (or at least, hasn't rotted away). Thus, the researchers concluded this was all evidence Lucy fell to hear death.
If she had fallen from the tree heights where chimps sleep, she would have been approaching 60 kph by the time she crashed into the ground. This, the authors inferred, would have been enough to do the damage they documented.
Too many breaks to believe
A sixty kilometres an hour "crash" does sound rather fatal. Certainly, falling from that height has killed chimpanzees. In fact, ~1.5% of all chimp deaths observed in the Gombe population (the one Jane Goodall famously studied) were the result of a chimpanzee rapidly leaving a tree. Or, to phrase it another way, over the course of 47 years of study 2 chimps were observed to fall to their death.
This doesn't sound quite as common as you'd think. What are the odds that our most famous family member died in such an uncommon way? Well, the more you compare these chimps to Lucy, the fewer things add up. For example, an "autopsy" was only performed on one of the chimps who fell to their death: an adult male called Rix. As expected, he died of broken bones. However, despite landing on his legs his injuries were nowhere as severe as the 11 distinct fractures documented for Lucy. In fact, the post-mortem revealed that none of his limb bones broke.
Comparing Lucy's "injuries" to other hominins with broken bones raise yet more questions. Australopithecus sediba is a hominin only known from Malapa Cave. This cave is at the bottom of a steep drop. It's believed that Au. sediba, along with the many other animals found at the bottom of the hole, fell down this "death trap" and died. No surprises there.
Some researchers believe they've found evidence of fatal compression fractures consistent with such a fall. The same sort of fractures recently found in Lucy. However, like Rix the chimp these injuries - despite being fatal - are nowhere near as severe as those documented in Lucy. Notably, their ribs didn't break, whilst Lucy's did. Allegedly.
Reviewing the reviewers
In short, Lucy's "injuries" seem way too serious to have occurred in a fall. So, either she suffered the worse fall ever seen outside of our species, or the method used to identify this damage is throwing up a lot of false positives. And I'm not the only one skeptical of this. Science Magazine quotes Owen Lovejoy - a prominent palaeoanthropologist - as describing the damage as so severe "you couldn't do that with a shotgun blast".
On the other hand, this counter-evidence is rather circumstantial. One dead chimp and two 1.9 million-year-old fossils aren't really enough to make a rigorous comparison. Then again, there are arguably just as many holes in the evidence for Lucy having a fall.
For example, the key line of reasoning that led the researchers to conclude it was a fall and not, for example, the result of some sort of animal attack leaves a lot to be desired. It effectively boils down to "falls are more common in modern humans and result in more broken bones than animal attacks". Even though they were examining a more animal-friendly population (rodeo riders) it hardly seems like a solid comparison. After all, we do know that our family occasionally got on an animal's bad side.
To put it simply, the evidence that Lucy fell out a tree is rather poor. At the same time, we can't say for sure she didn't fall either. But then we also can't say she wasn't murdered by pixies. Being unable to rule out an explanation doesn't make it valid. Nevertheless, the new data produced by this research is incredible. It will likely lead to many more discoveries about our most famous family member.
Including, perhaps, whether or not she did really fall out a tree.
Summary
New research claims to have found many fractures in Lucy's bones, indicating she died by falling out a tree. However, others who died after a fall don't match this pattern of injury.
References
Kappelman et al., 2016. Perimortem fractures in Lucy suggest mortality from fall out of tall tree
L'Abbé, E.N., Symes, S.A., Pokines, J.T., Cabo, L.L., Stull, K.E., Kuo, S., Raymond, D.E., Randolph-Quinney, P.S. and Berger, L.R., 2015. Evidence of fatal skeletal injuries on Malapa Hominins 1 and 2. Scientific reports, 5.
Teleki, G., 1973. Group response to the accidental death of a chimpanzee in Gombe National Park, Tanzania. Folia primatologica, 20(2-3), pp.81-94.
Williams, J.M., Lonsdorf, E.V., Wilson, M.L., Schumacher‐Stankey, J., Goodall, J. and Pusey, A.E., 2008. Causes of death in the Kasekela chimpanzees of Gombe National Park, Tanzania. American Journal of Primatology, 70(8), pp.766-777.
