In the arid expanse of Ethiopia’s Afar region, a handful of ancient teeth have upended long-held beliefs about our evolutionary past. Newly published research in Nature reveals that two distinct species of human ancestors—one from the genus Homo and another from Australopithecus—lived side by side between 2.6 and 2.8 million years ago. This discovery not only challenges the traditional, linear view of human evolution but also paints a far more intricate picture of our ancestral tree.
The teeth, thirteen in total, were unearthed over several years at the Ledi-Geraru archaeological site. According to BBC, ten of these teeth belong to a species of Australopithecus, while three are attributed to an early, as-yet-unnamed member of the Homo genus. The finds were made during a decades-long project aimed at piecing together the puzzle of early human ancestry in northeastern Ethiopia, a region renowned for its rich fossil record and home to the famed “Lucy” specimen of Australopithecus afarensis.
What makes this discovery particularly striking is the overlap in time and place between these two hominin lineages. For years, the prevailing view was that Australopithecus—an upright-walking but small-brained ancestor—had vanished before the arrival of the first Homo species. However, as Dr. Kaye Reed, co-author of the study and research scientist at Arizona State University, put it, “Here we have two hominin species that are together. And human evolution is not linear, it is a bushy tree, there are lifeforms that go extinct.” Reed’s remarks, cited by CNN, capture the growing realization among scientists that the story of human evolution is far from the simple, straight line from ape to modern human that many imagine.
The newly discovered teeth were found in sediment layers that have been precisely dated using volcanic ash containing tiny crystals called feldspars. As Christopher Campisano, another study author, explained, “We can date the eruptions that were happening on the landscape when they are deposited. And we know that these fossils are interbed between those eruptions, so we can date units above and below the fossils. We’re dating the volcanic ash of the eruptions that were happening while they were on the landscape.” This dating method, made possible by the active tectonic and volcanic environment of the Afar region, allowed researchers to pin down the ages of the teeth with remarkable accuracy.
The Australopithecus teeth, found between 2018 and 2020, have been dated to approximately 2.63 million years ago, while the Homo teeth, discovered in 2015, are from about 2.59 million and 2.78 million years ago. The overlap in these dates provides compelling evidence that both groups inhabited the same landscape at the same time. According to Brian Villmoare, the study’s lead author, “The new finds of Homo teeth from 2.6 to 2.8 million-year-old sediments confirm the antiquity of our lineage.”
Yet, while the teeth offer tantalizing clues, they also raise as many questions as they answer. The Australopithecus teeth have features not seen in either A. afarensis or another ancient hominin, garhi, suggesting they may belong to a previously unknown species. “Once we found Homo, I thought that was all we would find, and then one day on survey, we found the Australopithecus teeth,” Reed told CNN. “What is most important, is that it shows again, that human evolution is not linear. There were species that went extinct; some were better adapted than others, and others interbred with us—we know this for Neanderthals for sure. So anytime that we have another piece to the puzzle of where we came from, it is important.”
The fossil record in the Afar region is notoriously patchy, in part because the ancient landscape was shaped by shifting rivers and lakes that deposited only thin layers of sediment—layers that sometimes preserved the remains of our ancestors and the animals they lived alongside. Dr. Stephanie Melillo, a paleoanthropologist not involved in the study, noted that “erosion in rivers and lakes were at a low level and only a little bit of dirt was deposited in the Afar. That deposited dirt contains the fossils—of our ancestors and all the animals that lived with us. When there is little deposition, there are few fossils.”
Reconstructing the environment in which these ancient hominins lived, researchers found that the Afar region of 2.6 to 2.8 million years ago was a far cry from the dry, semi-desert landscape of today. Instead, it was a patchwork of wetlands and grasslands, with rivers that flowed only part of the year and shallow lakes that expanded and contracted with the seasons. According to Reed, “We have a fossil giraffe species that was eating grass, which probably indicates they were stressed as they eat trees and bushes almost every place else.” The implication? The environment was in flux, and food sources may have been scarce or unpredictable.
One of the most intriguing questions arising from the discovery is whether Australopithecus and Homo competed for the same resources. To answer this, the research team is examining isotopes in the tooth enamel and microscopic scratches on the teeth, hoping to uncover what each species ate. “Were the hominins eating the same thing? We are trying to find out by examining isotopes in their teeth and microscopic scratches on their teeth,” Reed said. Understanding their diets could shed light on how these two groups managed to coexist—or whether competition drove one to extinction.
Despite the excitement, the researchers are cautious about drawing firm conclusions until more fossils are found. “We know what the teeth and mandible of the earliest Homo look like, but that’s it,” Villmoare told BBC. “This emphasizes the critical importance of finding additional fossils to understand the differences between Australopithecus and Homo, and potentially how they were able to overlap in the fossil record at the same location.”
For now, the teeth serve as a reminder that human evolution is anything but straightforward. As Reed put it, “Whenever you have an exciting discovery, if you’re a paleontologist, you always know that you need more information. You need more fossils. More fossils will help us tell the story of what happened to our ancestors a long time ago—but because we’re the survivors we know that it happened to us.”
This latest find from the Afar region not only adds a new chapter to the story of our origins but also underscores just how much we still have to learn about the tangled roots of the human family tree.
