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New Human Ancestor Raises Questions about genus Homo

Dr. Juliet Brophy

On the corner of Dr. Juliet Brophy's desk is a skull fossil. "We have Australopithecus africanus, known as Mrs. Ples, that’s my favorite fossil. Everytime I see her I get all dressed up," she says. 

Dr. Brophy, a paleoanthropologist at LSU, is part of the team that discovered a new human ancestor, Homo naledi. The naledi fossils were recently found in a cave in South Africa, in an small area called “The Dark Zone.”

"The genus Australopithecus is the one right before our genus, the genus Homo," explains Brophy. 

Homo naledi is already differentiating itself from other species. For one, remains of fifteen individuals have been found. Other species have been determined based on as little as one tooth, "and now we show up and we have 190 teeth," she says. Having entire skeletal pieces, "that’s huge, unprecedented in paleoanthropology," says Brophy, adding "we definitely knew that we were making history."

Second, Naledi has a mixture of both modern and primitive features. Brophy explains that "the shape of the skull looks more modern. But the size of the skull is only about a third of modern humans."

It was conventionally thought that as the brain got larger, teeth got smaller. Large brain size led to developments like using fire to cook, and knives to cut food. Because brains were working harder, the teeth didn’t have to. That was the theory. But with Homo nailed, Brophy says, "we have a small brain size and small teeth. That is not what we expected. That was not the trajectory."

They still don’t know how old the fossils are. That’s the next step. "If it comes out to be less than a million," she says, "well then the evolutionary tree is a lot more bushy than we previously thought."

This discovery of Homo naledi has thrown a wrench into the theory of human evolution. "We had some preconceived ideas of what the genus Homo meant. And we need to redefine that to really understand what it means," she explains.