by KATE WONG
Hand, skull and foot bones from Homo naledi—a newly discovered human species—are part of a vast collection of fossils recovered from Rising Star Cave in South Africa. PHOTO/Kate Wong
When scientists unveiled the fossil remains of a newly discovered human species from South Africa called Homo naledilast September, the find electrified audiences around the world. It was an astonishing haul: some 1,550 specimens representing at least 15 individuals, recovered over just a few weeks of intensive excavation from the Rising Star Cave system outside Johannesburg. But it was the researchers’ favored explanation for how the remains ended up in the cave, more than the fossils themselves, that captured the public imagination and jolted the paleoanthropology community. They proposed that this creature—whose geologic age is unknown but who was clearly primitive; it had a brain the size of an orange—had deliberately disposed of its dead there. Many experts consider this behavior exclusive to our own far brainier species, H. sapiens.
Now an outside researcher has published the first formal critique of that provocative interpretation of the remains in a scientific journal. Members of the team that made the discovery dispute her claims, but other observers think that some of her criticisms are valid—and that the team has yet to make a convincing case that H. naledi deliberately disposed of the bodies in the cave.
Cavers discovered the H. naledi fossils in a chamber some 10 meters underground in Rising Star. To reach this inner sanctum, named the Dinaledi chamber, they squeezed through passages less than 25 centimeters across and climbed steep, jagged rocks in what would have been pitch darkness if not for their headlamps. How, the researchers wondered, did the fossils end up in such a remote part of the cave system?
To answer that question, geologist Paul Dirks of James Cook University in Queensland, Australia, and his colleagues analyzed the cave’s geology and features of the bones for clues. Bones can accumulate in caves by any number of mechanisms: For example, floodwaters can wash them in from their original resting place and carnivores can bring their kills in from outside. But such situations tend to produce fossil assemblages that contain a mix of animal species. And one of the most distinctive aspects of the Rising Star site is that H. naledi is the only medium or large animal species found there.
Scientific American for more