The recently-discovered species Homo naledi may have had a pint-sized brain, but that brain packed a big punch. New research by Ralph Holloway and colleagues — that include researchers from the University of the Witwatersrand, Johannesburg, South Africa — published in the Proceedings of the National Academy of Sciences examines the imprints of the brain upon the skulls of this species, called endocasts. The research highlights the humanlike shape of naledi’s tiny brain, surprising scientists who studied the fossils. These findings draw further into question the long-held belief that human evolution was an inevitable march towards bigger, more complex brains.
Naledi lived in southern Africa about southern Africa between 236,000 and 335,000 years ago, originating at the same time as modern humans, according to current dating.
The anatomy of naledi’s frontal lobe was similar to humans, and very different from great apes. Naledi wasn’t alone. Other members of our genus, from Homo erectus to Homo habilis and the small-brained “hobbits,” Homo floresiensis, also share features of the frontal lobe with living humans. But earlier human relatives, like Australopithecus africanus, had a much more apelike shape in this part of the brain, suggesting that functional changes in this brain region emerged with Homo. “It’s too soon to speculate about language or communication in Homo naledi,” said coauthor Shawn Hurst, “but today human language relies upon this brain region.”
The back of the brain also showed humanlike changes in naledi compared to more primitive hominins like Australopithecus. Human brains are usually asymmetrical, with the left brain displaced forward relative to the right. The team found signs of this asymmetry in one of the most complete naledi skull fragments. They also found hints that the visual area of the brain, in the back of the cortex, was relatively smaller in naledi than in chimpanzees — another humanlike trait.
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, “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.”
The researchers seem to be looking for something that nature seems not to provide: an ape-like missing link. They probably cannot accept that such a being may not exist any more than physicists and chemists centuries ago could conceive of a universe that didn’t need ether or phlogiston. Don’t expect them to give up the search any time soon.
See also: At Aeon: Homo naledi buried dead which suggests that maybe humans are not special, of course
Homo naledi had sophisticated but small brain