Telling the tale of human origins, one fossil tooth at a time

[INTRO MUSIC] FLORA LICHTMAN: Hi, it’s Flora, and you’re listening to Science Friday. Where did we come from? How did humanity, with our complicated civilizations and all of our human quirks and foibles come to be? This is one of science’s most basic questions, and much of what we about the answer traces back to important fossil finds in Ethiopia.

The paleoanthropologist Yohannes Haile-Selassie has been key in that hunt for answers. He’s helped discover some of the most important known hominid fossils, like the bones used to describe the 2.5 million year old Australopithecus garhi, and the first pieces of a 4.4 million year old partial skeleton of Ardipithecus ramidus. You know Ardi. We all know Ardi. And fossils of the 5.8 million year old Ardipithecus kadabba.

His list of finds also includes specimens from Australopithecus afarensis and more modern species of Homo, including Homo erectus– so many branches of the human family tree. Today, he’s the director of the institute of Human Origins at Arizona State University, and a professor in the School of Human Evolution and Social Change. And he’s here to talk to us today about some of the big questions in human origins research and his own origin story. Welcome to Science Friday.

YOHANNES HAILE-SELASSIE: Pleasure to be with you, Flora.

FLORA LICHTMAN: We’re delighted to have you. You’ve made these many spectacular finds. I read that originally, you went to school for history that you didn’t really know that paleoanthropology was a thing. Do I have that right?

YOHANNES HAILE-SELASSIE: Yeah. So my first degree, which is from Addis Ababa University in Ethiopia, was in history and history, as a subject, relates to written history. But there were a couple of courses on archeology, one of them being early man. And I really loved that course, because that was the first course that introduced me to fossils and also introduced me to the name Australopithecus, which I had a lot of problems saying, but clearly that interest built up when I started to work for the Ministry of Culture in Ethiopia, where I was assigned to work in a paleoanthropology laboratory where there were so many fossils.

And when I started going out to the field with paleoanthropologists as antiquities officer, seeing the fossils on the ground was another excitement, which increased my interest in them. And luckily, I ended up being a good fossil finder. Some of them, I didn’t know what I was finding at that time, but they were really great fossils, some of them, fossils of human ancestors.

FLORA LICHTMAN: What are these digs like? Are you camping? Is it hot? Paint me a picture.

YOHANNES HAILE-SELASSIE: OK. Well, when I take you to the field, first of all, what I can tell you is you’re going to a place where the temperatures go as high as 110 degrees. It’s very hot. And you’re going to be living in a tent, in a small tent, for four to five weeks. And you’re going to have to think about everything that you need while you’re out there and all of your stuff. You have to pack and get ready.

But once you’re in the field, you get up at 6:00 in the morning, eat breakfast at 7:00, OK, and go out to the field looking for fossils. Now, what do we do once we are out in the field? A lot of people, when I come back from the field, they usually ask me how was the dig? And I’m like, I was not digging. I was just walking around with my eyes on the ground, looking for fossils and identifying whatever fossils we can find and catalog them at the end of the day. So–

FLORA LICHTMAN: OK. Is this like beachcombing? You’re just walking around with your head down.

YOHANNES HAILE-SELASSIE: Exactly. Exactly. Well, that’s what you do for 99% of the time. Now sometimes, you might end up having an excavation. And one good example from my site is the discovery of the partial skeleton of Australopithecus afarensis, about 3.6 million year-old partial skeleton. And we excavated that locality for five years in a row.

Now, when do you decide when to do excavation? Now, a lot of times, you might end up finding a few specimens just coming out of the ground. And you find different elements of the body coming out. That’s a good sign that there might be more, and you end up excavating and definitely will find more. Otherwise, for most of the time, you just keep walking and walking for hours every single day.

And in the end, you end up collecting probably hundreds of fossils or even sometimes three or four, depending on how rich the locality that you’re exploring is. Some of the days, you may not find anything, and you get disappointed going back to your camp. But other times, you don’t mind staying until like 7:00. Even if it’s dark, you just stay because you’re finding so many exciting things.

And once you’re done and you come back home, everything that you think about is, when am I going to go back to do the same thing? So that’s how addictive fieldwork is. So if you were to go to the field, that’s the feeling you would have. But again, you might feel tired at the end of the day, but there’s always that excitement because of what you have found or throughout the day, especially if you found something good.

FLORA LICHTMAN: It’s like a treasure hunt. You mentioned at the beginning that you had a knack for this. You happen to be good at finding fossils. Is there a trick to it? Do you have a secret?

YOHANNES HAILE-SELASSIE: Well, there’s no trick to it. It’s just about how you train your eyes and what you focus on. So when you’re exploring and doing surveys with your eyes on the ground, you’ve got to tell your brain exactly what you’re looking for. Because your eyes are going to probably focus on the bigger items on the ground than the smaller ones. But you can train your eyes to blur the bigger ones and focus on the little ones.

Because unfortunately, the fossil record is filled with isolated teeth more than anything else. And teeth are small. So most of the discoveries that I’ve made started with isolated teeth or isolated fragments of other parts of the body. So it’s about how you train yourself in addition to eventually learning to what you’re finding.

So that was not my expertise at the beginning. So whatever I found, which were really good, were identified by others, my seniors, who had the experience doing that kind of work. But eventually, I developed the knowledge as well. And now, every fossil that we find in the field, I have to identify not only in terms of what element it is, but also what animal it belongs to. So that’s how you develop the experience.

Otherwise, there is a lot of luck associated with finding fossils. Sometimes, it’s just being at the right place at the right moment because the fossils that you see this year on the surface, if you leave them there next year, they may not be there. Because there is erosion, they could be displaced. There are animals who trample the bones and they can kick them and remove them and rebury them sometimes. So when I say you have to be at the right place at the right time, that’s also part of the luck that you need to actually find good fossils.

FLORA LICHTMAN: There’s some serendipity there.

YOHANNES HAILE-SELASSIE: Yes. Correct.

FLORA LICHTMAN: Why are there places with just enormous numbers of human remains? Why are there certain fossil hotspots?

YOHANNES HAILE-SELASSIE: So when you think about where are the hotspots located, O course, most of our evolutionary history happened in Africa. So when you think about all the discoveries that we have up until, I would say, 2.2 million years, 1.9 million years, there were no hominin ancestors that lived outside Africa. And in Africa specifically, if you look at all these localities that we go explore every single year, they’re all located in the rift system.

So the rift system is an area where the Earth has been opening up because of plate tectonics. It’s been opening up, exposing these deep trenches with sediments that have been buried for millions of years. And as the rift gets more wider and wider, what you will see is that the sediments start getting eroded. So whatever life lived in those ancient sediments is what gets exposed. So there is a geological component to why these areas are really significant.

Now, you got to also think about primates are tropical animals. We’ve always lived in the tropics, and it’s less likely that you would find the earliest human ancestors, like further to the north in the colder regions. And if we had rift systems like the East African Rift system somewhere else in Africa, could there be a possibility to find fossil hominins? I wouldn’t say no. We could. But again, our target has always been this region. But I wouldn’t be surprised if there are other areas where these early hominins lived, but we’re not finding them because the geological context is not convenient for us to look for these fossils.

FLORA LICHTMAN: I’ve heard this field is very competitive and fierce and secretive. Do you find that to be true? And if so, why do you think that is?

YOHANNES HAILE-SELASSIE: I would have to admit that it is true because I think in the late 1900s, when there were so many discoveries coming out of sites in Africa, people were actually studying whatever they were finding by themselves and publishing it. And there has been a lack of data-sharing. That, in fact, might have made individual researchers famous, but it was not really good for the science because that thing is changing right now. And we can see the difference. People have started communicating, collaborating, and sharing data.

And some of it is because of rules from funding agencies where you have to really share data. Otherwise, you’re not going to get money to do your research. But now, not only fossils, but when you look at the genetic research that is being done, it’s highly collaborative. I think not only do we think about sharing the data, but also the timing of when we share the data.

Because in our field, things change really quickly. New ideas come up as new fossils are coming out of the ground. And if we can’t really communicate that on a timely manner, we’re delaying the progress in the science. And it looks like every paleoanthropologist now understands how this field has to operate moving forward. And if we have to make it relevant to the society, we are the ones who should now change that trend and make sure that data-sharing is the norm, not the exception.

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FLORA LICHTMAN: I’ve got to take a break, but when we come back, I want to zoom out from the tiny teeth in the field to the very big picture. You up for that?

YOHANNES HAILE-SELASSIE: Sure. No problem.

FLORA LICHTMAN: What does it mean to be human?

YOHANNES HAILE-SELASSIE: Well, that’s the $64 million question. What is it to be human? We have a very long evolutionary history. We’re talking about an evolutionary history of about six to seven million years. And documenting that evolutionary history is probably the hardest, particularly when you think about how do we reconstruct our past as paleoanthropologists? We tackle this question by going out to some remote areas to find ancient fossils of our ancestors, not only our ancestors, but also fossils of other animals who lived with them.

Because to understand really how we became human involves really understanding the circumstances in which we kept evolving for the last seven million years. So compiling all that data to actually answer the question of how do we came about to be who we are today and where we’re going in the future is going to be the most challenging question for all of us. And we’re still trying to piece together evidence to actually answer that question.

FLORA LICHTMAN: It’s interesting. From the outside, I keep seeing these tantalizing discoveries. We covered one pushing back the timeline of when modern humans appeared, possibly. Just recently, I saw a science paper suggesting we have ghost ancestors– not Neanderthals, not Denisovans– some other hominid population that early humans bred with. Do you feel like this is an exciting time for your field?

YOHANNES HAILE-SELASSIE: Very exciting because now in the 21st century, we have so many tools that we didn’t have in the 20th century. So now we’re talking about at the genetic level– not just shape, and form of fossils, but also deep diving into the genetic components of this early human ancestors. And yes, 30 years ago, we wouldn’t have thought about a ghost species. But now, thanks to the developments in genetics, we can actually see that there was a lineage that we haven’t sampled in the fossil record yet, which could be part of our evolutionary history.

So hopefully, we will keep pushing the ability of genetic analysis further back in time. Right now, it might be limited to a few hundred thousand years, but eventually, we’re going to probably push it back in time to the millions so that we can–

FLORA LICHTMAN: You think so?

YOHANNES HAILE-SELASSIE: Well, we hope. Because it’s not just the DNA. There’s also some analysis on ancient proteins now that is pushing the time back to millions of years. So there is a lot of hope that there’s going to be another component to our analysis that we can further understand our evolutionary history.

FLORA LICHTMAN: When I first started covering this field, there was a lot talk about a missing link. Do people still think about it that way?

YOHANNES HAILE-SELASSIE: I would say no, because missing link has always been a misnomer. In the old days, people referred to missing link as the ancestor that we shared with the chimpanzees and gorillas, and that’s what used to be called the missing link. But there is no missing link. There are so many links that we still haven’t recovered, but they’re not missing links. So that idea has completely changed. Now, we don’t really think that there is something called missing link.

FLORA LICHTMAN: I know that there’s this issue in paleoanthropology of Western scientists parachuting in to Africa, the colonial legacy. How do you think about that in your field?

YOHANNES HAILE-SELASSIE: I think a lot of us agree that it has to change, and there has been a lot of movement. Communities have not been involved as much in terms of what we do as researchers. We go to their area. We collect fossils. We go out. We describe the fossils and publish.

Do we really communicate with the local communities in terms of what we’re doing in their area, what the significance of the discoveries we’re making, what it means to them? Those were the lacking points that we’re trying to change by making sure that communities are engaged, and also make sure that they benefit from the research that we’re doing.

And there are so many ways to do that. And some of it is by collaborating with local institutions, opening programs in paleoanthropology in universities. As a matter of fact, ASU has an MOU with one of the local universities in Ethiopia, Samurai University. And right now, we’re trying to open a new paleoanthropology master’s program. So this is a huge agenda that paleoanthropologists, anthropologists all over the world are discussing right now.

And I can see that in a lot of ways, some changes are happening. And I can see that a lot of our researchers are actually expanding community engagement in so many ways and making sure that they benefit from the research that we’re doing.

FLORA LICHTMAN: What’s the most exciting discovery of the last couple of years for you?

YOHANNES HAILE-SELASSIE: Most of the discoveries in the last couple of years have been related to genetics. All these results that we’re finding in terms of how the ghost species that you mentioned is one, but we’re also seeing some of these early human fossils that we’ve had for decades that we couldn’t figure out what they were like the Denisovans, for example, we’ve had fossils from China for many, many decades that we didn’t realize were what they could be.

And now, genetics is linking all these fossils to either Denisovans. So all of the research, genetic research that’s happening, that has been happening in the last couple decades is really exciting. And it’s really changing how we understand our origins.

FLORA LICHTMAN: That’s so fascinating. Is there something you dream of finding, just where you’re going out and you’re like, you know what I really want to find is this?

YOHANNES HAILE-SELASSIE: When I started in this field, my dream was to find the earliest human ancestor. And I found Ardipithecus kadabba, which was great.

FLORA LICHTMAN: And you did.

YOHANNES HAILE-SELASSIE: Mission accomplished, yeah. But then after I graduated and then wanted to have my own project and I started this project [INAUDIBLE], my dream changed. Because this time, I wanted to have a site of my own that I can work at instead of working, collaborating with others at other sites. And that was also another mission accomplished, because I now have one of the best mid-pliocene sites in the world, which is called [INAUDIBLE] site.

And when I got there, of course, what’s the next dream? The next dream was because these sediments are somewhere between 3.83 and 3.5, 3.4 million years ago, my research question was to actually understand how Lucy’s species, Australopithecus afarensis, was connected to its potential ancestor, Australopithecus anamensis. So my question was, can I find anything that would inform me about this transition from the sediments that are between 3.6 and 3.8 million years ago? And that’s another dream.

And we found so many fossils from this time period, including finding the most complete cranium of Lucy’s ancestor, anamensis, from 3.8 million years ago. So now, I’m also working in the sediments that are between 3.2 and 2.9 million years ago. And now, I have a dream. My dream is, can I find the earliest Homo in this deposits?

Because we have sediments at Ledi-Geraru project that are about 2.8 to 2.9. And this project is actually led by one of our faculty here, Professor Kay Read, who found this earliest Homo at 2.8 million years ago. So now, my dream is, can we push that record a little bit older because we have the sediments?

So what that tells you is that I never had a single dream. My dreams have always changed with the circumstances, and so far, my dreams have been realized. And now, I have a new dream that I hope will be realized as well. So that’s how my dreams have been evolving through time.

FLORA LICHTMAN: That’s perfect. Why should people care about this research?

YOHANNES HAILE-SELASSIE: That’s interesting question. Positive discoveries have always been interesting to the general public. Now, as generations change, what we’re hearing now is beyond the excitement of these discoveries, people have started asking, so what? What do they mean to me? How are they relevant to me?

And that’s the big challenge for scientists. How can they answer that question? So what does it mean to me, is a question that you really need to address by reframing how you tell the story, the human story, based on what you’re finding and what you’re publishing.

But also, how do we connect it to our future? Now, every discovery comes with interpretations that include the animal communities, the environment, and everything. That was part of the ecosystem when this early human ancestors lived. And today, we talk about climate change. Now, climate change is not something new. How did our ancestors cope up with the climate change that have happened so many times in their evolutionary history?

So there is a connection between what we can learn from the past to actually understand what we might expect in the future. So that’s the connection that we need to create for people to really understand and appreciate the value of studying our past. The past is not just the past. The past is also about understanding our future. When we say all humans are connected, we’re lucky that we have now so many ways to explain that connection to our ancestors.

As I said, the genetic work is really amazing, and it’s connecting so many dots that we were not able to connect using just fossils in the near shape and form. We’re pushing that connection way back to the millions of years by tracing who was the ancestor of the Neanderthals? Who was the ancestor of the Denisovans, and Homo erectus and beyond, Homo habilis? You can go all the way to about six million years ago.

So we know where we came from, where we started. But where are we going? So why did Homo erectus go extinct, or why did you Homo habilis go extinct? Is Homo sapiens, our species, going to go extinct? How can we reconstruct the sequence of events that have happened in the past to make it relevant to us today?

So that’s why we investigate our past in so many ways, not only in terms of how we change, in terms of how our brains became larger or how we became more efficient bipedal walkers, but also, what’s the next step? Where are we going? This is something that we can learn by compiling what we’ve learned from the past.

FLORA LICHTMAN: I mean, what could be more relevant and existential than whether we make it?

YOHANNES HAILE-SELASSIE: Well, that’s the big question. Yes. That’s the big question.

FLORA LICHTMAN: Dr. Yohannes Haile-Selassie is the Director of the Institute of Human Origins at Arizona State University and a professor in the School of Human Evolution and social. change. Thank you so much for talking to me today.

YOHANNES HAILE-SELASSIE: Well, thanks for having me, Flora.

FLORA LICHTMAN: It was really a pleasure. And if you have questions about where we came from or where we’re going that you think Science Friday could answer, give us a call, 877-4SCIFRI. This episode was produced by Charles Bergquist. I’m Flora Lichtman. Thank you for listening.

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