New research from the University of Texas-Austin speculates that Lucy, the famous 3.2 million-year-old fossil of an ancient human relative, may have died by falling out of a tree. Such a fate would be an ironic twist for a skeleton that’s been intensely studied for clues about how much time hominins capable of walking on two legs still spent climbing trees.
The evidence for Lucy’s demise? Computer tomography scans of the breakage patterns in her bones, which orthopedic surgeons have identified as similar to injuries sustained in a hard fall or car accident, and which UT anthropologist John Kappelman says Lucy must have suffered close to the time of death.
Credit: John Kappelman, University of Texas at Austin
This finding is not supported by everyone in the paleoanthropological community, but it raises an interesting question: How much does looking at bones tell us about how our early relatives lived, or how we eventually evolved? John Hawks, a professor of anthropology at the University of Wisconsin-Madison, and Tracy Kivell at the University of Kent, are two anthropologists trying to solve ancient mysteries with fossil evidence—such as skull size, finger structure, and even plants traces stuck in teeth.
They sound off on what potentially killed Lucy, and discuss how researchers are using new fossil finds—and turning new technology on old ones—to piece together the hominin family tree.
John Hawks is a paleoanthropologist at the University of Wisconsin-Madison.
Tracy Kivell is a biological anthropologist at the University of Kent in Kent, England.
JOHN DANKOSKY: This is Science Friday. I’m John Dankosky. It’s being described as the cracking of a 3.2-million-year-old cold case. How Lucy, the famed fossil skeleton of an early human ancestor, may have died by falling out of a tree. The clues– new high-resolution CT scans of her bones. The research out of the University of Texas has been disputed by some anthropologists, including some who’ve worked extensively on Lucy in the past. More about that in just a bit.
When we saw this paper, it made us curious. What are the stories that bones are telling us about our ancient human relatives, and how do we know they’re true? How are new technologies expanding what we can know about how they lived and how our singular branch sprung from the tree?
Here to trace the science behind the stories of our millions-year-old kin are my guests– John Hawks, first, a Professor of Anthropology at the University of Wisconsin-Madison. John Hawks, welcome back to the show. Thanks so much for joining us.
JOHN HAWKS: Thanks. Great to be here, as always. And if you want to join us, our phone number is 844-724-8255. That’s 844-SCI-TALK. So tell us about your reaction to this paper. We’re now hearing that Lucy may have died from a heart impact, possibly falling out of a tree. What’s the evidence that’s being pointed to here?
JOHN HAWKS: Well, the team who analyzed the bones got to scan them for the first time, because the bones came to the United States on tour. And they took them into a high-resolution scanner at the University of Texas. And they spent a lot of time reconstructing the fragments of the bones.
And on Lucy’s upper right arm, her humerus, that upper right arm bone, has got the head of it, the side that connects to your shoulder, sort of punched into the bone. And the outsides of it is sort of crushed outwards. And people have seen that since they found the fossil. And they sort of assumed, well, this is damage that probably happened after it was fossilized, as it was underground, under high pressure.
But the team of John Kappelman and his colleagues looked at it. And they said, you know, this looks funny to us. It looks like the kind of break that you see when somebody is thrusting out their arm to stop a fall. And that was where they really started their detective work.
They looked across the rest of the skeleton. They found some other breaks that they thought were indicative of breakage that happened around the time of death, not healed breaks. We can tell when there are signs of healing, something that wasn’t healed but happened when the bones were possibly still fresh. So that was where they went to say, hey, something happened here, and it’s really something we need to explain.
JOHN DANKOSKY: So there has been some criticism of this research, and you’ve asked some questions yourself. Why is there a debate over this? I think part of it is people really feel like they know this fossil. Here’s a fossil that’s been out of the ground for more than 40 years.
And when you’ve got this iconic image of something, especially the folks who’ve worked on it for a long time, what’s really unusual is when a new study comes out and says, hey, I found something new. And the people who have known these things for 40 years say, hey, no, no way. That can’t be. And you look at that and say, what’s going on here?
There is a lot of damage that happens to fossils when they’re buried in the ground and fossilized. As that process of mineralization is happening, they’re buried under tons of sediment. And what you want to see in a case like this is that there’s been a comparison made to other fossils of other kinds of animals that are found along with these fossils. And you say, oh, OK, this pattern is either like the other fossilization damage, or it’s different. In this case, the paper didn’t have that kind of information. So it made people, like me included, very skeptical.
JOHN DANKOSKY: So there’s not CT scans of bones from other animals found just around the site?
JOHN HAWKS: Exactly. The thing is that you look at that and you say, wow, this is like a forensic case. And the first thing you do if you want to prove that something is a gunshot is look at a lot of gunshots and other kinds of things. It’s like you watch CSI. They’re going to shoot a gun into the ballistic gel and show, OK, we can recognize this pattern.
And that’s what hasn’t been done in this case, understandably, right, because we don’t go running all kinds of animal fossils through high resolution scanners all the time. But it’s one of those things that, as the technology progresses, we demand more and more evidence to document what we’re finding.
JOHN DANKOSKY: I want to bring into our conversation Tracy Kivell, who’s a paleoanthropologist at the University of Kent in the UK. She focuses specifically on hand bones, which we’ll talk about in just a moment. Tracy, welcome to the show.
TRACY KIVELL: Hi. Thank you very much for having me.
JOHN DANKOSKY: First of all, I want to ask, what would it tell us, do you think, about Lucy’s species or anything about the time she lived if it turns out she really did fall out of a tree?
TRACY KIVELL: Well, I guess there are many aspects about Lucy’s skeleton and many other early fossil humans that suggested they were– they said they had the potential to climb trees. But it’s been a huge debate in our field basically since Lucy was discovered, whether or not the features of her skeleton that suggest she was climbing in trees were actually something that she was using, or were they just sort of relics or retentions from a more arboreal ancestor. So the idea that potentially this evidence of this actual behavior would be is quite helpful.
JOHN DANKOSKY: So in your work, Tracy, you look specifically at the anatomy of the hand in fossil hand bones. So what sorts of questions can a hand answer? What can you learn from a hand?
TRACY KIVELL: Well, I think the hands are exciting, because they can tell us about two big questions in human evolution, potentially whether or not we’re using our hands for climbing in trees and suspending in trees and how long into our human evolutionary history did we do that, and when did we stop using our hands for locomotion and become fully committed to walking on two feet on the ground.
But it also can tell us about when we used tools or when we began to use tools and when a human hand is very well-known for our dexterity. But we don’t know exactly when that dexterity evolved and when we started to use tools and to make tools. And so our hands are directly involved in both of those big questions about human evolution.
JOHN DANKOSKY: If we look at Lucy as an example, what do her hand bones tell us about how she lived or what she did?
TRACY KIVELL: Well, that there are a lot of hand bones for Lucy’s species. But unfortunately, we don’t have articulated or a hand skeleton that belongs to one individual, which means that we are little bit more limited in what we can say about what Lucy may have done with her hands.
But we can put together sort of a composite skeleton of the hand. And when we do that, we can tell that potentially her fingers were a little bit longer relative to the length of her thumb than in a human hand. She didn’t have quite as long fingers as we see in a chimpanzee or bobono.
But her fingers seem to be a little bit longer potentially than ours are, which is an indication that maybe she is still spending at least some time in the trees. And also, her finger bones are a little bit more curved than a human’s. And both of those things are an indication that she had the potential to spend some time climbing in trees.
JOHN DANKOSKY: If you’ve got questions about Lucy, this famous human ancestor, 844-724-8255 or 844-SCI-TALK. John Hawks, you were one of the anthropologists looking at a large cache of fossils found in South Africa last year that turned out to be a completely new species of human ancestor. Could you walk us through the treatment of those bones and that discovery a little bit?
JOHN HAWKS: Sure. We were obviously immensely lucky. We did not expect that, in the Rising Star Cave, we were going to find what turned out to be a cache of at least 15 hominid individuals, at least 1,500 fossil specimens that we found there so far.
And that was really a remarkable thing. To analyze those, you think of– we’ve got discoveries in our field where people work on the discovery literally for decades, where you have so many things you want to do. You want to compare it to every other fossil that we’ve ever found. You want to have high-resolution scanning done. You want to have experts look at that stuff.
We brought in a team of more than 50 people around the world to analyze these fossils. We’ve done some high-resolution surface scanning of them. We’ve been doing micro CT scanning of the material. We brought in experts like Tracy, who work on different elements of the anatomy. We really did this all in parallel, which was a fun process, because we got to see the insights that people were developing who studied the hand for their whole lives or studied the teeth and put together that picture.
The cool thing about it was being able to apply technology and being able to apply different expertise all at once. You discover things that you wouldn’t have expected otherwise. The hand is sort of a cool story with Homo naledi, because the wrist bones, the fingertips, all these things are very human-like. But the fingers like in Lucy’s species are relatively curved. And that makes us think that Homo naledi was probably climbing to some extent, even though it had a lot of human-like elements to its hands.
JOHN DANKOSKY: I’m wondering, if Tracy could quickly pick up on some of what we learned about the hands from that discovery.
TRACY KIVELL: Yes, yeah. As John mentioned– well, first, we were extremely, extremely lucky. It’s an amazing source of fossils. Yeah, one aspect of the luckiness is basically that we found a hand that was basically in articulation. So we know it belongs to a particular individual, and that allows us to say a lot more about the hand function than just trying to piece together bits and bobs from different individuals.
And as John said, the fingers are really quite remarkably curved. They’re even more curved than what we see in Lucy, which is quite surprising, given the very human-like aspects of some of the other parts of her skeleton. And also, within the hand, there are aspects of the wrist and the thumb that show features that we only see in humans and Neanderthals.
And these features, most of them relate to a reorientation of the way of our wrists and how our wrists accommodate high stress that happens when we manipulate objects during tool use and tool making.
And those features that we see and those changes that we see in humans and Neanderthals have been interpreted as being adaptations to a commitment to stone tool use and making complex stone tools. And we see those adaptations in Homo naledi but in combination with these really curved fingers. So it’s this sort of completely different signals and different aspects of the hand skeleton.
JOHN DANKOSKY: I’m John Dankosky. This is Science Friday from PRI, Public Radio International. Tracy, it sounds like we can learn so much about our ancestors from hands. But you face a lot of challenges being a hand expert, don’t you?
TRACY KIVELL: Yes. Well, until Lee Berger and his team discovered the Homo naledi and the new species, australopithecus sediba, which was discovered a few years ago as well in South Africa, we really had a very limited fossil record in terms of hand bones, at least in terms of hand skeletons, that it was always, for the most part, fragmentary remains from isolated bones for which we didn’t know whether they belonged to the same individual.
And most of the time, we didn’t even know what species they belonged to. And so it has been quite difficult to sort of say something more concrete about the evolution of hand use. But thankfully, these new discoveries are making my job a lot easier.
JOHN DANKOSKY: Well, I would assume, John Hawks, that something that would make everyone’s job a lot easier is if you could just scan more bones like this. Why aren’t all of these bones scanned, and what are some of the challenges to doing that?
JOHN HAWKS: Well, the technology has progressed a lot. But 15 years ago, the state of the art was, I’m going to scan one bone or maybe a skull and will accurately estimate the size of the inside of it or something. The technology is progressing.
But also when we deal with human evolution, we find these fossils in many different countries, all of which have heritage issues that they want to make sure that they’re responsible custodians of their country’s heritage. Museums are involved. And they want to make sure that, as they’re curating these objects, they’re being responsible in it.
And we today in science, much more about sharing than was ever true in the past. Today, the state of the art is you put your data online when you publish your paper that describes it. It’s that thing of people should be able to look at your data.
But when you deal with heritage objects, there’s a lot of times this instinct that’s sort of like art history. You know, like the museum has this thing, and you want to make sure that any possible rights to photographs of the thing are conserved appropriately and so on.
We’re moving into a realm where people are more used to the idea of sharing data openly, where having a data set of scans is something that is essential to do new work on new fossils. And I think that the field is changing. But it’s one where that process of change is still happening. It’s a great progress this week that the team that scanned Lucy released a few of the bones as models online so people can look at these and can print them out. And I think that we’re going to see more and more of that.
JOHN DANKOSKY: Are there other technologies that you think, John, would make your life, your job easier, where you could make some new discoveries if just you had that one thing?
JOHN HAWKS: [CHUCKLES]
I’ll tell you what. If you had a device like a tricorder from Star Trek that could look into rocks and see what was inside of them, that would make a lot of difference. I got to say, we learn so much from new techniques– things like doing microsampling of calculus, that tartar that builds up on teeth. And we find evidence of ancient plants inside of that, the plants that individuals were eating. So you learn about diet that way.
We scan with the synchrotron super high-energy X-rays through these fossils and create very high-resolution images of teeth. And you can see the growth increments in the teeth. Technology makes a difference to this. But a lot of what we do is just going out in the field and looking and looking and looking.
The discovery at Rising Star was a couple of guys who were avocational cavers who said, can we help look for things? And by God, the first cave they went into looking, they found something incredible.
JOHN DANKOSKY: Tracy, we just have a few seconds. Do you have something that you’d love to see next that would help you do your job?
TRACY KIVELL: Ooh, a time machine. That would be helpful.
That would answer a lot of questions.
JOHN DANKOSKY: Well, I was going to say. A time machine, I know some people are working on that. We might not get that any time soon. But I want to thank our guests. Tracy Kivell, a paleoanthropologist at the University of Kent in the UK. Thank you so much for your time. I really appreciate it.
TRACY KIVELL: Oh, thank you very much.
JOHN DANKOSKY: And thanks also to John Hawks, a professor of anthropology at the University of Wisconsin-Madison. Thank you, John.
JOHN HAWKS: Thank you. Much appreciated.
Christie Taylor was a producer for Science Friday. Her days involved diligent research, too many phone calls for an introvert, and asking scientists if they have any audio of that narwhal heartbeat.