Humans have a new ancestor. A new hominin species that likely lived at the same time as the "Lucy" species in Ethiopia is described in a study published in Nature today. The species would have lived between 3.3 and 3.5 million years ago — a timestamp that further muddles human evolution, while also lending support to the idea that numerous hominins co-existed during the middle Pliocene.
We don’t know if the Lucy species gave rise to modern humans
Up until recently, human evolution was viewed as a fairly simple tree. Sure, it had a number of branches up at the top, but its trunk was basically one straight line, researchers thought. But with the discovery of Kenyanthropus platyops in 1999, and now with this new hominin species, that idea has had to evolve as well. The truth is that we don’t know if the Lucy species that was discovered in 1974 gave rise to modern humans. "The complexity of human evolution — species emerging and all that — extends further back in time" than researchers previously thought, says Fred Spoor, a human paleontologist at University College London who helped describe Kenyanthropus platyops and who didn’t take part in this new study.
Credit: Yohannes Haile-Selassie
In the study, researchers analysed jawbones and teeth that were found in Ethiopia in 2011, about 22 miles from where fossils belonging to "Lucy" species, Australopithecus afarensis, have been found. Although the size and the shape of the new hominin resemble that of afarensis, the researchers argue that some of the features are very distinct from it. And so, the researchers named the new hominin Australopithecus deyiremeda. "Deyiremeda" is a mish-mash of words from the region that mean "close relative."
Lucy and deyiremeda "were living next door to each other."
"With this discovery we confirm that there were multiple hominin species during the middle Pliocene," explains Yohannes Haile-Selassie, a paleoanthropologist at the Cleveland Museum of Natural History and a co-author of the study. "We also show that A. deyiremeda and A. afarensis were living next door to each other."
The researchers make a good case for a new species, Spoor says. But there's still a chance that this fossil belongs to the Lucy species. Males and females can be very different, and the variation seen in this specimen could play into that somehow, Spoor says. "They give good reasons for why it’s a different species, but I will only completely agree with it when I see it myself."
Early human ancestors were diverse
No one knows what deyiremeda looked like, or how it behaved. The only thing we know for sure is that these hominins were different from modern humans in terms of their facial morphology, size of their teeth, and most likely their brain capacity. Researchers also aren’t sure whether the Lucy species and deyiremeda ever interacted. "These questions are difficult to answer because the fossils don't tell us anything about them," Haile-Selassie says. Still, both Spoor and Haile-Selassie think that it’s possible that they co-existed. And if they did, they may have avoided each other, Haile-Selassie says — "if only to avoid extinction."
"There is still a lot more to learn about our evolution," Haile-Selassie says. "Early human ancestors were as diverse as other animals in the past and in the present." Discovering new species like this one means that scientists will eventually have to figure out which one of those middle Pliocene hominins is the ancestor of our genus Homo. "When A. afarensis was the only known species from the middle Pliocene, it was the only candidate to be the ancestor," Haile-Selassie says. Now, we have at least three candidates. This means that researchers will need to learn a lot more about deyiremeda and platyops, he says— "at least" as much as we know about Lucy.