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Disappointment! Homo naledi Is Younger than Previously Thought

Homo naledi

As we noted here the other day, according to the line formerly promoted by scientists including paleoanthropologist Lee Berger, Australopithecus sediba was an “ancestor for our genus,” Homo. They’ve walked that one back. And now another “ancestor” has received similar treatment.

In 2015, researchers introduced the world to Homo naledi. This was greeted with breathless headlines: “Trove of fossils from a long lost human ancestor” (PBS), “Homo naledi: New species of human ancestor discovered in South Africa” (CNN), and more. For a hominid fossil, being an ancestor of humans requires originating in the right time period. Yet when Homo naledi was published, the fossil creature had no date associated with it. So we got expressions of skepticism like this from anthropologist Carol Ward of the University of Missouri, in The Atlantic:

Without dates, the fossils reveal almost nothing about hominin evolution, beyond supporting the growing realization that there was much more species diversity than previously thought.

This didn’t stop researchers from speculating that the fossil could be close to three million years old:

Prof Lee Berger told BBC News that he believed they could be among the first of our kind (genus Homo) and could have lived in Africa up to three million years ago.

What was so attractive about a figure of three million years old, or perhaps less? Simply this: as with A. sediba, that’s about when paleoanthropologists think Homo evolved from Australopithecus. However, as ABC News acknowledges, fossils demonstrating this transition are currently lacking:

Scientists have long talked about a “missing link” between very old fossils, more than 3 million years old, and much newer ones that they believe are clearly ancestors of today’s human beings. There is a gap in the fossil record, so far unexplained.

Some scientists hoped that Homo naledi would prove to be the fossil to bridge the gap. Those hopes were fated to be dashed, however, as Homo naledi now turns out to be much too young – indeed, one tenth the desired age. From the BBC News report, “Primitive human ‘lived much more recently’“:

A primitive type of human, once thought to be up to three million years old, actually lived much more recently, a study suggests.

The remains of 15 partial skeletons belonging to the species Homo naledi were described in 2015.

They were found deep in a cave system in South Africa by a team led by Lee Berger from Wits University.

In an interview, he now says the remains are probably just 200,000 to 300,000 years old.

Oh. The BBC article links to a tweet with a photograph of Berger and an interview with him where he says that “Homo naledi is 200,000 and 300,000 years old.”

The BBC report continues:

Although its anatomy shares some similarities with modern people, other anatomical features of Homo naledi hark back to humans that lived in much earlier times — some two million years ago or more.

“These look like a primitive form of our own genus — Homo. It looks like it might be connected to early Homo erectus, or Homo habilis, Homo rudolfensis,” said Prof Berger’s colleague, John Hawks, from the University of Wisconsin.

Although some experts guessed that naledi could had lived relatively recently, in 2015, Prof Berger told BBC News that the remains could be up to three million years old.

New dating evidence places the species in a time period where Homo naledi could have overlapped with early examples of our own kind, Homo sapiens.

Prof Hawks told the BBC’s Inside Science radio program: “They’re the age of Neanderthals in Europe, they’re the age of Denisovans in Asia, they’re the age of early modern humans in Africa. They’re part of this diversity in the world that’s there as our species was originating.”

This fails to emphasize the main news, however, namely the chasm of age between how old Homo naledi was previously thought to be, and how old it’s thought to be now. An age of 200,000 to 300,000 eliminates naledi entirely from the evolutionary story of our species, Homo sapiens.

Undeterred, proponents of Homo naledi can’t bring themselves to abandon the fossil as representing a transitional species, with evolutionary roots stretching back millions of years. Says John Hawks, according to the BBC:

We have no idea what else is out there in Africa for us to find — for me that’s the big message. If this lineage, which looks like it originated two million years ago was still hanging around 200,000 years ago, then maybe that’s not the end of it. We haven’t found the last [Homo naledi], we’ve found one.

New Scientist echoes the view:

“This is astonishingly young for a species that still displays primitive characteristics found in fossils about 2 million years old, such as the small brain size, curved fingers, and form of the shoulder, trunk and hip joint,” says Chris Stringer at the Natural History Museum in London.

[…]

Based purely on its strange anatomy, H. naledi seems to belong somewhere near the very base of the “true human” family tree — an idea suggested in some studies of the fossils.

But we know that the first early humans appeared more than two million years ago. If H. naledi is just 300,000 years old, some researchers might argue that it can’t belong to the base of our family tree. It’s too young. Perhaps it even had a modern-looking ancestor and later evolved primitive-looking features.

But it is, in fact, still perfectly possible that H. naledi really does belong somewhere near the base of our human evolutionary tree.

The species might have evolved more than two million years ago, as one of the earliest “true” humans, and then survived, unchanged, for hundreds of thousands of years.

“It could lie close to the origin of the genus Homo, suggesting that this is a relic species, retaining many primitive traits from a much earlier time,” says Stringer.

They’re still hoping naledi is a long-lost transitional form linking Homo to earlier groups like Australopithecus. If true, that would require unearthing other naledi fossils, much older than what we have already. Sure, it could happen. Who knows? But the available data on Homo naledi shows those creatures as living long after any line leading to humans branched off. As far as anyone can say at this moment, there’s no evidence for an ancestral relationship.

The BBC article does say this: “A study outlining the dating evidence is due for publication in coming months.” We look forward to that.

But Carol Ward was correct when she said that “without dates, the fossils reveal almost nothing about hominin evolution.” The hype was wrong. Certainly it was premature. Homo naledi, in all likelihood, is not your ancestor.

Photo: Foot, Homo naledi, by Lee Roger Berger research team (http://elifesciences.org/content/4/e09560) [CC BY 4.0], via Wikimedia Commons.