New H. naledi data changes what we know about our evolutionary tree

New H. naledi data changes what we know about our evolutionary tree
GULSHAN KHAN/AFP/Getty Images

In 2015, news broke that scientists had discovered evidence of a previously unknown member of the human evolutionary family tree, based on studying several skeletons found deep in a cave in South Africa. The new species was called Homo naledi; judging by bones from several individuals, it possessed a unique blend of primitive and modern evolutionary qualities. One paleontologist described it for National Geographic: “You could almost draw a line through the hips — primitive above, modern below.” [National Geographic / Jamie Shreeve]
But it was unclear how old the bones were — which meant no one knew how long ago this creature had lived, and how it might fit into the evolutionary history of Homo sapiens. Because the brain was estimated to be roughly the size of an orange (which is relatively small for a hominin), scientists guessed at the time that it must have been quite close to the root of the Homo genus family tree — which would make it more than 2.5 million years old. [New York Times / John Noble Wilford]
On Tuesday, the research team announced a surprising result: The Homo naledi species is significantly younger than expected. Using six different dating methods, the team studying Homo naledi found that the remains of individuals they’ve been studying are between 335,000 and 236,000 years old. [National Geographic / Michael Greshko]
Here’s why this matters: The age of Homo naledi now suggests that at that point in time, in the midst of our own evolution as Homo sapiens, the hominin family tree was more diverse than originally thought — with more hominins, and more diverse kinds of hominins, on the planet at the same time. [New York Times / Associated Press / Malcolm Ritter]
To get a better sense of how and when various hominins coexisted, the Smithsonian Museum of Natural History clusters several species near the top of the family tree (closest to the present day). Some you’ve probably heard of, and others you may not have: Homo rudolfensis, Homo habilis, Homo heidelbergensis, Homo erectus, Homo floresiensis, Homo neanderthalensis, and Homo sapiens (us). Previously undated, Homo naledi isn’t currently on the tree. [Smithsonian Museum of Natural History]
No one knows for sure how much these species overlapped and if and how any of them interacted. But on Tuesday, National Geographic described the time period that Homo naledi are now considered part of: “Around 230,000 to 330,000 years ago, there weren’t just precursors to anatomically modern humans on the landscape: There would have been Neanderthals in Europe and Asia, Denisovans in Asia, potentially some Eurasian pockets of our ancestors Homo erectus, as well as the forerunners of H. floresiensis. Amid this pantheon, H. naledi would be the first known that lived in Africa at that time, other than some scattered evidence of archaic forms of H. sapiens.” [National Geographic / Michael Greshko]
This latest discovery about Homo naledi isn’t the only recent shake-up to our understanding of our family tree — nor it is the only one having to do with smaller, more primitive-seeming hominins. Homo floresiensis, a species often called the “hobbit” species because it only grew to be about 3.5 feet tall (and which is considered to have existed as recently as 60,000 years ago), was originally thought to have evolved from a shared ancestor of modern humans. But in April, researchers announced that it was far more primitive than originally thought, and that it likely followed its own evolutionary path from Homo habilis, the oldest known member of the human genus, rather than a shared ancestor of ours closer up the family tree, like Homo erectus. [Guardian / Melissa Davey]
Which means that as recently as 60,000 years ago, Homo sapiens shared the planet with hominins that could have actually been relatively far from us on the evolutionary tree. And as of today’s news, it seems 200,000 years ago the precursors to Homo sapiens possibly overlapped with Homo naledi. “Our ancestors did not live in a single-species world the way we do,” paleoanthropologist Alison Brooks told the Washington Post. “The real take-home message of this paper is that we were not alone until very recently.” [Washington Post / Sarah Kaplan]
The questions these discoveries raise are endless. Here are a few great ones that the Washington Post raised after the Homo naledi news broke: “Was Naledi a result of, and perhaps a contributor to, hybridization within the Homo family tree? Could Naledi be responsible for some of the stone tools found in South Africa during the period it was alive? Should paleoanthropologists shift their focus from East Africa to the continent's less-studied southern regions?” [Washington Post / Sarah Kaplan​]
One thing’s for sure: The Smithsonian will need to do some updating to its exhibit on evolution.



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