There’s a new branch on the human family tree. Anthropologists say they’ve found a new human ancestor, who lived 3.5 million years ago, right beside Australopithecus afarensis on the plains of what is now Ethiopia.
Casts of the upper and lower jaw. Credit: Laura Dempsey
You may have heard of the species of human ancestor called Australopithecus afarensis, or at least its most famous specimen: Lucy, the partially complete skeleton of a female hominin. Researchers say the newfound species co-existed with Lucy and her species, and the discovery is a remarkable new piece in the puzzle of humanity’s origins.
But it raises as many questions as answers.
Anthropologist Yohannes Haile-Selassie and his team have named the new species Australopithecus deyiremeda. They found fossilized upper and lower jaw fossils at a paleontological dig site in the Afar region of central Ethiopia in 2011, and after four years of study, they’ve published their findings in the journal Nature.
Based on radiometric dating and the geology of the soil in which they found the fossils, Haile-Selassie and his colleagues say that the fossils are about 3.3 million to 3.5 million years old. A. deyiremeda’s teeth and jaws look quite a bit different from Lucy and her fellow A. afarensis—it’s this difference that led anthropologists to classify them as a separate species. It’s likely that the two species evolved to eat different foods that required different kinds of biting and chewing.
Credit: Yohannes Haile-Selassie
Researchers say it’s the most conclusive evidence yet that multiple species of hominins coexisted before 3 million years ago. Previously, Haile-Selassie had found the fossilized remains of a partial foot in the same area, but the team doesn’t have enough evidence to say whether the foot is also from A. deyiremeda.
Until recently, scientists were fairly sure that only one hominin species existed at a time, gradually giving rise to the next through evolution. But now we know it can be hard to tell exactly where an earlier species ends and a later species stops, because the changes are so gradual. If there were two or even three species of hominin coexisting in eastern Africa 3 or 4 million years ago, it wouldn’t be without precedent. Much more recently, between 50,000 and 60,000 years ago, anatomically modern humans in Eurasia coexisted and interbred with Neanderthals.
The A. deyiremeda jawbones were found just 22 miles from the site where researchers found Lucy’s remains in 1973, and where other A. afarensis remains have been found since. Scientists can’t be completely sure how these two species are related to each other yet, and they’re still working out the exact shape of the family tree between them and modern humans.
Still, their proximity raises interesting questions about how these two distinct species might have interacted. Were they peaceful neighbors, or did they fight over space, food, and water? Could, and did, they interbreed? Anthropologists don’t know yet—we’re only just beginning to understand the complex history of humankind.