The small brains of Homo naledi raise new questions about the evolution of human brain size. Big brains were costly to human ancestors, and some species may have paid the costs with richer diets, hunting and gathering, and longer childhoods. But that scenario doesn’t seem to work well for Homo naledi, which had hands well-suited for toolmaking, long legs, humanlike feet, and teeth suggesting a high-quality diet.
According to study coauthor John Hawks, a paleoanthropologist at the University of Wisconsin–Madison. “Naledi’s brain seems like one you might predict for Homo habilis, two million years ago. But habilis didn’t have such a tiny brain–naledi did.”
“Maybe brain size isn’t all it’s cracked up to be,” said Hawks. “It opens the door for us to say that maybe they were more capable than we might assume; maybe it isn’t just (brain) size.”
The research shows that the more complex structural features of brains may not solely be a consequence of size, and it suggests that modern humans, Neanderthals and Homo naledi may have a common ancestor.
“Archaeologists have been too quick to assume that complex stone tool industries were made by modern humans,” said [co-author Lee] Berger. “With naledi being found in southern Africa, at the same time and place that the Middle Stone Age industry emerged, maybe we’ve had the story wrong the whole time.”