You've met 'Lucy.' Now ASU scientists unearth another clue to the origin of humans
Reed and a team of international scientists believe they have added a new member to humanity's family tree — a yet undocumented species of hominid, or upright ape, that walked the east African grasslands more than 2.6 million years ago. She and the team made the discovery when they found three collections of ancient primate teeth lying on the ground during fossil searches at the Ledi-Geraru Research Project Area led by ASU.
Scientists believe the new species could offer clues about the conditions that produced humanity's ancestors, though this species was likely not a direct predecessor to homo sapiens. The species lived in an area and time at which future humans may have first emerged, according to the fossil record.
Scientists know very little about the new species so far, Reed said. A collection of teeth is useful for understanding the animal's diet, but arms, legs, and skulls provide a fuller picture of how it moved around its habitat. Those clues help researchers understand the conditions in which the species survived.
'Evolution doesn't work like that'
Those insights could shine light on a critical, but poorly understood, chapter in human evolution. The new species may have been one of the last members of a dying family of human ancestors known as the australopithecus genus, which includes the famous 'Lucy,' whose fossil was unearthed in 1974. As its relatives were dying out, this new species would have watched the rise of humanity's genus, homo, which was the first to commonly use stone tools and eat meat.
'If it's a different species of Australopithecus… that means (Lucy) either went extinct or somehow evolved into this new species,' said Reed, part of the Institute of Human Origins at ASU. 'The fact that it also occurs at roughly the same time as the genus Homo suggests to us that there was a change in the climate and the habitats, which you had to change to survive.'
With the new species, Reed believes at least four species of upright apes were living in east Africa at the same time, including two australopithecus, one homo, and a species from an offshoot called paranthropus.
Scientists don't know much about the transition from Australopithecus to homo because the fossil record during that period is surprisingly slim, Reed said. But this new discovery makes at least one thing clear: As with much of evolution, this transition was not a straightforward line. The process of human evolution is full of dead ends and overlaps, with multiple species of upright apes evolving alongside each other, some successful and some not.
'Everybody always posts that thing where there's a hunched over ape, and then there's a kind of upright ape, and then something with a bigger brain, and it's just from one to one to one," Reed said. "Evolution doesn't work like that.'
Even the distinctions between ancestors and descendants is sometimes unclear. Reed had to grapple with this complexity when she and her colleagues attempted to identify the teeth they had found. The team considered multiple alternatives, including the possibility that the teeth belonged to transitional forms of already known species. While some species distinctions are obvious, Reed said, some are almost a matter of opinion, pointing out that some scientists might have classified the new teeth as a variant of the 'Lucy' species.
'Another scientist that I know might put these teeth into (Lucy's species). He doesn't care about what he would consider the minor differences,' Reed said.
A famous discovery: On a November day 50 years ago, a scientist found 'Lucy' and rewrote our origin story
Still searching for more clues
The appearance of the new species could also help scientists better understand why humanity's closest ancestors, the homo group, emerged when they did. Some scientists have argued that homo species evolved partially as a response to a drier habitat with more grasslands, but this new species shows that an Australopithecus species could also survive in that new, dry environment.
'You have longer dry seasons, so animals are stressed. Many that we see in Lucy's time are eating trees, but then they switch to grass, and in that time period we find the Australopithecus is different from what it was,' Reed said.
More clues about the new species' diets will help Reed and other researchers understand how it interacted with other walking apes and whether this was a case where humanity's ancestors had to out-compete their relatives to grab hold of the future.
'If they ate the same thing, it's going to be tough for one of them to survive … and so maybe one of them out-competed the other,' Reed said. 'But maybe they weren't eating the same thing, and that's how they split when it got really dry.'
Traces of carbon and nitrogen in ancient teeth can indicate what kinds of plants or meat the animal ate. To discover that an australopithecus was scavenging meat would make it a much more direct competitor with human ancestors, Reed said.
Otherwise, scientists have many miles to walk before they can fully understand the new creature they might have brought to light. That will mean many more hours searching for the right sediments and pacing, meticulously, in the east African heat.
'To find this stuff is really exciting,' Reed said. 'We just have to find more information to put the puzzle together.'
Austin Corona covers environmental issues for The Arizona Republic and azcentral. Send tips or questions to austin.corona@arizonarepublic.com.
Environmental coverage on azcentral.com and in The Arizona Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust.
This article originally appeared on Arizona Republic: ASU scientists may have found a new species related to humans
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