A new paper fills in some gaps in our species’ Paleolithic history. University of Arkansas anthropology professor and researcher Lucas K. Delezene was an author on the paper, "New Discoveries of Australopithecus and Homo from Ledi-Geraru, Ethiopia." The findings stem from the discovery of thirteen teeth uncovered in a research area in northeastern Ethiopia.
Ozarks at Large's Jack Travis invited Delezene to the Bruce and Ann Applegate News Studio One to talk more about the findings and their implications for how we humans understand our species’ history.
Delezene: We just published a paper in the journal "Nature" that describes new hominin fossils.'Hominin is the word we use for humans and our closest living and extinct relatives. And these fossils belong to two very distinct types of early hominin. The fossils are dated between 2.6 and 2.8 million years ago, and one set of fossils would be the earliest members of our genus, which we call Homo, and then the other is a different type of hominin that goes by the fancy scientific name of Australopithecus.
Travis: People might know Australopithecus from that famous discovery?
Delezene: The site that we work at in Ethiopia is called Ledi-Geraru. The next project area over is called Hadar. At Hadar in the 1970s, a fossil called Lucy was discovered. She belongs to a species we call Australopithecus afarensis. And the site of Hadar is one of the richest fossil sites for early hominins in the whole world. Our site is just right next door, but it’s, geologically speaking, younger, so we have sediments that come after what is at Hadar.
Travis: What implications does this have, finding all these teeth together?
Delezene: At Hadar the sediments stop at around 3 million years ago, and Lucy’s species basically disappears from the fossil record then. That doesn’t mean the species went extinct, but that we no longer find fossils of it. Fast-forward to about 2 million years ago—a gap of about a million years—we see Australopithecus is gone. Instead, we have things that are on the human lineage, Homo, and this other really weird cousin of ours called Paranthropus. The idea for years has been that Lucy’s species is kind of the common ancestor of us, Homo, and this other weird cousin named Paranthropus. Our research at Ledi-Geraru fills in that temporal gap. What we found wasn’t Paranthropus. We found this late-surviving Australopithecus, like Lucy’s species, but the teeth look different.
Travis: Is this a new species or the same as what we found with Lucy?
Delezene: We did not name a new species in the paper. The Australopithecus material we have is about 300,000 years younger than Lucy’s species, and it does look different. But if you think about how, over generations spanning 300,000 years, change would accumulate, it is possible Lucy’s species could have changed into the form that we have at our site of Ledi-Geraru. But it does look different. We stopped short of naming a new species and just said that we have Australopithecus living side by side with early members of the human lineage as well.
Travis: What does that mean for our understanding of hominins?
Delezene: I teach a large introductory biological anthropology course at the university. One misconception I address is that people imagine the famous "March of Progress", where there’s one line extending from our ancestor to us today and each form becomes more human-like. The truth is humans are part of a much broader hominin family tree. A lot of these species are not particularly human-like; they have their own distinct combination of traits. At Ledi-Geraru, we have two divergent branches of that tree, Homo and Australopithecus, occupying the same area. Imagine today there’s only one hominin species: us, and we're spread around the world. At 2.6 million years ago, there were two different species that likely had to parse up resources. They would have done something slightly different from each other. This isn’t the first time we’ve discovered evidence for two hominin species living together after 2 million years ago—Homo living with Paranthropus. We’ve just found another example. The way I like to think about it is that, we're not exactly sure why our lineage became the super successful one that replaced all of these others, but what we're seeing is evidence that Homo, the human-like lineage, is able to coexist with these other different types of hominin in different places at different times. And so it suggests something about being adaptively versatile. And maybe that competition with these species in the past is what ultimately drove us to be the adaptively flexible and geographically widespread species that we are today.
Travis: But back more than two million years ago, they would have been coexisting. Can you describe what that might have looked like? Were they sharing campsites? Working together?
Delezene: The answer is unknown at the moment. If we put aside our discovery, from younger sites where Homo and Paranthropus coexisted, there are indications their diets were very different. In Kenya and Tanzania, Paranthropus seems to focus on grass—its cranial traits suggest a really weird diet—and Homo becomes broader in dietary proclivities and starts using tools. At Ledi-Geraru we don’t have data yet on diet, but one might imagine they were eating different things. That’s future research. So far, our fossils are jaws and teeth. We don’t know what their faces looked like, their cranial capacity, arms or legs. That matters for reconstructing what these species did. For now we can say there were two lineages with different teeth—what that means about diet and daily life we want to figure out next.
Travis: What’s next for this research?
Delezene: Back to the field. We published 13 teeth. We want more fossils to test our hypotheses. We’d love to find fossils from the rest of the body. We want to look at evidence for diet, reconstruct lifeways. This site also has some of the oldest evidence for stone tool use—2.6-plus million years old. Though not associated with these fossils, we want to know if Homo origin is linked to tool use.
Travis: Congratulations—it’s a big publication.
Delezene: Thank you.
Travis: This isn’t your first large discovery.
Delezene: In 2015 I was part of a team in South Africa at a site called Rising Star, where about 1,500 fossils were found. In 2015 we named a new species called Homo naledi. The fossils there are about 250,000 years or slightly older. The material in Ethiopia is over 2.5 million years old—ten times older. The South African material overlaps in age with early Homo sapiens but is very different: small body, small brain, distinctive hands suggesting climbing. In Ethiopia we have some of the oldest fossils that belong to our genus. Potentially the ancestor of all these diverse forms of Homo. We sometimes think of humans as big-brained, tool-using exemplar of what it means to be a hominin—but Homo naledi shows until recently there were small-brained, small-bodied hominins. The stuff in Ethiopia is getting close to the origin of the genus, and South Africa shows a descendant.
Travis: Why is it important to get research like this publicized?
Delezene: One thing I think is that we're all interested in what it means to be human and where we come from. But in a broader sense, the money that we use to fund the research from grants and things like that aren't just used for field research going out and finding the fossils. It's used back at the lab at the University of Arkansas and elsewhere to train students. Very few go on to be anthropologists; many go on to be dentists or doctors because I focus on teeth. We link fieldwork with lab work to train students for careers beyond anthropology. In my lab we have more biology majors working with us than anthropology majors, because many are pre-med or pre-dental. If research funding dries up we lose training opportunities for students, which impacts future careers in medicine and dentistry.
That was Lucas K. Delezene, speaking with Ozarks at Large’s Jack Travis in the Bruce and Ann Applegate News Studio One. You can visit the UofA website to read the paper in full and learn more about the U of A’s anthropology department.
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