MARY LOUISE KELLY, HOST:
Maybe you've seen the T-shirts or the mugs, the silhouette of an ape standing up straighter and straighter, finally morphing into a modern coffee-drinking man. Scientists have long known human evolution was not so straightforward. NPR's Nate Rott reports on a new study that shows just how complicated it was.
NATE ROTT, BYLINE: Kaye Reed was walking across some northeastern Ethiopian badlands with colleagues back in 2018 when they found the first tooth, a premolar.
KAYE REED: And it was beautiful. And we could tell it was a hominin, meaning that it's something that walks on two legs and looks kind of like us.
ROTT: Reed is a paleoanthropologist and professor emerita at Arizona State University.
REED: And then suddenly, one of the Afar went, oh, my goodness.
ROTT: One of her Ethiopian colleagues had found another, and then they found another.
REED: And then I stood up 'cause we were down there looking, and I was sitting on a tooth.
ROTT: By the end of the search, they found 10 teeth, ancient teeth at more than 2.6 million years old. But Reed says they didn't match up well with any other known hominin teeth from that era.
REED: Obviously, science is a bunch of hypotheses that you put together. And our hypothesis is that this is likely a new species.
ROTT: A new species of Australopithecus, the genus that, for those of you who don't dabble in ancient human history, is believed to be distant, let's say, cousins to us. Even more exciting, Reed said, is a week later they found three more smaller teeth from roughly the same time period.
REED: And all three of those belong to the genus Homo.
ROTT: And genus Homo, for people who don't know, is?
REED: Is us. I mean, we are Homo sapiens.
ROTT: Reed and her colleagues' findings, published in the journal Nature, suggests that these different types of human ancestors were coexisting in this part of Africa millions of years ago. It's not the first documented case of hominin coexistence. But it raises a lot of questions, like was there interbreeding between the two groups, competition for resources, cooperation? Coauthor Brian Villmoare, a paleoanthropologist at the University of Nevada, Las Vegas, says they hope to learn more by further analyzing the teeth and doing more fieldwork. More broadly, though, he says the findings confirm what scientists have been saying for a long time.
BRIAN VILLMOARE: The human lineage is not unique.
ROTT: No species evolves in a straight, made-for-T-shirt line, Villmoare says. Evolution is more bushy, like a family tree.
VILLMOARE: You know, if you look at, like, apes now, so there are multiple species of ape alive all at the same time, you know? And monkeys and cats and dogs and all these things, right? So the point is that humans are not really special in the way we evolved.
ROTT: For example, he says roughly 2 million years ago, there were as many as seven species of hominins across Africa all living at once.
VILLMOARE: Even though there's only one species alive now, that's a fairly recent thing.
ROTT: Recent, at least in evolutionary terms. Nate Rott, NPR News. Transcript provided by NPR, Copyright NPR.
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