“There just hasn’t been any evidence one way or another,” said Susan Anton of New York University, who collaborated with Meave Leaky in describing the new fossils.
Rick Potts, director of the Smithsonian Institution’s human origins program, said he’s convinced the new fossils do represent a distinct species. Potts, who did not participate in the new work, added, “There will still be controversy over what to call these things.”
Whatever name the fossils eventually receive, one thing is certain, said Potts: The old picture of human evolution heading in a straight line — where an early species gave rise to a more advanced species and so on, until finally reaching modern humans — is all but defunct.
Instead, with each new find, human origins appear more and more complex.
“It does look like these are a lot of experiments in how to be a Homo species, doing slightly different things and looking a little different,” Anton said.
As researchers pull more early human fossils from the sedimentary rocks of East Africa, Potts expects to see more evidence of “evolutionary chaos” at the base of the human family tree. “That experimentation is a brilliant part of the evolutionary process.”
All of these groups likely made simple stone tools, Potts said. And yet, they left only a fragmentary picture of who they were — let alone what they ate or how they behaved.
“At the moment, all we’re doing is classifying heads,” said Bernard Wood, a paleoanthropologist at George Washington University who studied the mystery skull in the early 1990s and declared it likely represented a new species. “It will be a different ballgame when we can match heads with limbs. There are limb bones, but with no heads.”
Spoor cautioned that it’s still unclear if the different species of early humans interacted or interbred. “It’s not that we can say for sure that in one given month in one particular year that these species could meet each other and shake hands at the lake margin.”