Species had a frontal lobe very similar to that of people and unlike an ape’s
What makes humans so smart? For a long time the answer was simple: our big brains.
But new research into the tiny heads of a recently discovered human relatives called Homo naledi may challenge that notion. The findings, published this week, suggest that when it comes to developing complex brains, size isn’t all that matters.
In 2013, scientists excavating a cave in South Africa found remains of Homo naledi, an extinct hominin thought to have lived 236,000 to 335,000 years ago. Based on the cranial remains, the researchers concluded it had a small brain only about the size of an orange. Recently, they took another look at the skull fragments and found imprints left behind by the brain. The impressions suggest that despite its tiny size, Homo naledi’s brain shared a similar shape and structure with that of modern human brains, which are three times as large.
“We’ve now seen that you can package the complexity of large brain in a tiny packet,” said Lee Berger, a paleoanthropologist at Wits University in South Africa and an author of a paper published in the journal Proceedings of the National Academy of Sciences. “Almost in one fell swoop we slayed the sacred cow that complexity in the hominid brain was directly associated with increasing brain size.”
Since its remains were first retrieved, Homo Naledi has puzzled scientists. From head to toe, the ancient hominin displays a medley of primitive, apelike features and more advanced, humanlike characteristics.
“It’s this mosaic that is unlike anything we have seen or expected,” said Dr. Berger, who first discovered Homo naledi in the Dinaledi Chamber of the Rising Star cave system in South Africa. So far, researchers have found more than 2,000 fossils belonging to the human relatives, which have provided a portrait of what the species once looked like.
Homo Naledi had small teeth like a human’s, but their shape more closely resembles that of an ape’s. Its shoulders were also apelike, but arms, wrists and hands more humanlike. The fingers, though, were long and curved, and the thumbs appeared particularly strong. The spine was a combination of primitive and Neanderthal-like, the pelvis resembled that of another more distant human relatives, Australopithecus afarensis (dubbed Lucy), and the thighs also looked primitive.
Now, researchers have found that Homo naledi’s similarities with modern humans extend into the brain. After examining the imprints, or endocasts, from five Homo naledi skull fragment, the team found that the species had a frontal lobe that was very similar to that of modern humans and unlike that of an ape’s. The scientists also found that Homo naledi had an asymmetrical brain, with the left brain appearing more forward than the right, which is also seen in humans. Asymmetry in the brain is associated with higher levels of behavioral complexity, the team said.
Based on the regions of the brain that Homo naledi shared with modern humans, the authors suggest that it may have exhibited complex behavior. But what they did not say was what those behaviors may have been, said John Hawks, an paleoanthropologist at the University of Wisconsin, Madison, and an author of the paper.
“Is that aspect of the brain evolution central to talking or stone tool making? We don’t know enough to say that,” he said. He added that the finding does not mean that brain size is not important to creating a complex brain ? it is. Rather, size alone does not tell the whole story. “There’s something about shape that actually matters too,” he said.
Simon Neubauer, a physical anthropologist at the Max Planck Institute for Evolutionary Anthropology in Germany, said that because of its age, Homo naledi might be an outlier in a general hominin trend toward increasing brain sizes.
