New Human Species with Orange-Size Brain Discovered

Paleoartist John Gurch spent some 700 hours recreating the head of Homo naledi based on bone scans.

(Image credit: Mark Thiessen/National Geographic)

A newly discovered extinct human species may be the most primitive unearthed yet, with a brain about the size of an orange. But despite its small brain size, the early human performed ritual burials of its dead, researchers say.

This newfound species from South Africa, named Homo naledi, possessed an unusual mix of features, such as feet adapted for a life on the ground but hands suited for a life in the trees, that may force scientists to rewrite their models about the dawn of humanity.

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The scientists recovered more than 1,550 bones and bone fragments, a small fraction of the fossils believed to remain in the chamber. These represent at least 15 different individuals, including infant, child, adult and elderly specimens. This is the single largest fossil hominin find made yet in Africa. (Hominins include the human lineage and its relatives dating from after the split from the chimpanzee lineage.)

On average, Homo naledi stood about 5 feet (1.5 m) tall and weighed about 100 lbs. (45 kilograms). It had a tiny brain, only about 30.5 cubic inches (500 cubic centimeters) in size, making the organ about as large as the average orange. That's smaller than the modern human brain, which is about 73 to 97 cubic inches (1,200 to 1,600 cubic cm), but comparable in size to the brain of Australopithecus sediba. Australopithecines are likely the ancestors of the human lineage. [Australopithecus Photos: Anatomy of Humanity's Closest Relative]

"Modern humans are really unusual in that walking on two legs is pretty much all we do," study co-author Will Harcourt-Smith, a paleoanthropologist at Lehman College in the Bronx and the American Museum of Natural History in New York, told Live Science. "Homo naledi probably spent most of its time walking on two legs, but also spent some proportion of its time up in trees — whether to escape predators or nest at night, we don't know."

Prior research had uncovered another possible instance of an extinct human species disposing of its dead, in Atapuerca in Spain. This site also contained remains thrown to the bottom of a cave. "Those hominins were much larger-brained, much closer to modern humans in brain size," Harcourt-Smith said. "There's debate as to which species was at Atapuerca — probably Homo heidelbergensis, a close relative of Neanderthals."

The age of the fossils remains uncertain, since the chamber lacks many of the features that scientists normally rely on to date fossils. As such, scientists can't yet say where Homo naledi fits on the human family tree. Depending on its age, it could be a direct ancestor to Homo sapiens, or the ancestor of the species that gave rise to Homo sapiens. "At this stage, all we know is that it's reasonably primitive," Harcourt-Smith said.

The researchers did note that both Homo naledi and the "hobbit" Homo floresiensis had similarly tiny brains. Although the scientists said they could not as yet speculate on any evolutionary links between those two species, the researchers new findings revealed that small-brained, primitive-looking human species with fairly modern features did exist in the past. This suggests that the hobbit is no longer an anomaly, the researchers said.

Charles Q. Choi is a contributing writer for Live Science and Space.com. He covers all things human origins and astronomy as well as physics, animals and general science topics. Charles has a Master of Arts degree from the University of Missouri-Columbia, School of Journalism and a Bachelor of Arts degree from the University of South Florida. Charles has visited every continent on Earth, drinking rancid yak butter tea in Lhasa, snorkeling with sea lions in the Galapagos and even climbing an iceberg in Antarctica.