Homo Naledi

https://www.theverge.com/2017/5/9/15591814/homo-naledi-discovery-bone-dating-human-evolution
Two years ago, scientists announced the discovery of a puzzling new species of early human: Homo naledi. The 15 partial skeletons were uncovered deep inside a cave in South Africa — and featured human-like hands and feet, but surprisingly small brains the size of a gorilla's (a third the size of modern human's). The discovery of H. naledi, however, lacked one key piece of information: the age of the bones. Now, the team of researchers who uncovered H. naledi announced the fossils are between 236,000 and 335,000 years old, according to National Geographic. If the dates are confirmed, that means H. naledi is much younger than its primitive features suggest, and they may have lived around the same time our own species — Homo sapiens — was evolving.

The discovery, published today in the journal eLife, is likely to be controversial, because it could mean that the stone tools uncovered in South Africa from the time — called the Middle Stone Age — weren’t made by modern humans. Today’s research is controversial for another reason: the researchers describe the discovery of a second cave chamber, where a bunch of other H. naledi remains were found. That may confirm one contested hypothesis first put forward in 2015: that H. naledi used the Rising Star cave to bury its dead. That’s a very complex and modern behavior, and some scientists believe that such primitive humans couldn’t have performed it.

MUCH YOUNGER THAN ITS PRIMITIVE FEATURES SUGGEST
The first cave chamber, called Dinaledi, was discovered in 2013. It contained over 1,500 specimens of H. naledi — the largest single paleoanthropological find of its type in Africa. The chamber is deep underground, and could be accessed only by a team of female scientist-climbers specially selected to fit through a narrow, vertical shaft that was just eight inches wide at points. The second chamber, called Lesedi, is also similarly hard to reach, and contains remains from about 130 specimens, including one adult skeleton that’s very well preserved.

Both chambers only contain H. naledi remains (although some animal remains were found inside Lesedi). That suggests H. naledi used to site to bury its dead. And the discovery of the second chamber bolsters that hypothesis, according to the research team led by University of the Witwatersrand paleoanthropologist Lee Berger. “What are the chances that you have some natural phenomenon that has left accumulations of multiple bodies, adults and juveniles, in two far-separated parts of the cave, in very similar depositional circumstances — and we found both of them?” John Hawks, a paleoanthropologist at the University of Wisconsin-Madison, who’s part of the research team, told National Geographic. “It’s very difficult to believe that this is some kind of coincidence.”


But some disagree, saying that the bodies could have been deposited in the caves naturally — maybe they were washed there by floods. There are no artifacts in the cave, so it’s hard to interpret the meaning of the remains, Alison Brooks, a paleoanthropologist at George Washington University and the Smithsonian Institution who wasn’t involved in the research, told The Washington Post.

To date the H. naledi remains found in the first cave chamber, the researchers used six different dating techniques, each tried independently by two labs to confirm the results, according to The Washington Post. (The remains in the new cave chamber haven’t been dated yet.) The team analyzed the H. naledi teeth, the layers of calcite deposited through time on the bones, and the cave’s radioactivity — and determined the fossils date to between 236,000 and 335,000 years ago. That’s much younger than the team previously thought: H. naledi shares some features with early members of our genus that lived nearly 2 million years ago, so the researchers thought the H. naledi fossils would be around the same age. Today’s finding, however, dispels that, and could mean that H. naledi was a lingering lineage that arose about 2 million years ago, and stuck around at a time when a bunch of other early human ancestors roamed the planet.

HOW H. NALEDI FITS INTO THE HUMAN FAMILY TREE ISN’T CLEAR YET
In fact, during the Middle Stone Age, there were Neanderthals, Denisovans, and Homo erectus, as well as other hominins. How H. naledi fits into the human family tree isn’t clear yet. Could it be that H. naledi, not H. erectus, is our most immediate ancestor? It’s impossible to tell for now, but what’s clear is that the H. naledi discovery paints a much more complicated picture. And more research is needed before conclusions are reached.

“The past was a lot more complicated than we gave it credit for and our ancestors were a lot more resilient and lot more varied than we give them credit for,” Susan Anton, a paleoanthropologist at New York University who was not involved in the study, told The Washington Post. “We're not the pinnacle of everything that happened in the past. We just happen to be the thing that survived.”