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Bones of Contention: Is Homo Naledi a New Species?

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Posted October 3, 2015

The popular science press went bonkers last month with news that fossilized bones of a previously unknown hominid had been discovered in a cave system in South Africa. Dubbed Homo naledi by lead researcher and University of the Witwatersrand paleoanthropologist Lee Berger, these proto-humans appeared to have lived somewhere between 1 to 3 million years ago, used tools, walked upright, and may have buried their dead, a practice that has only been attributed to our own species, Homo sapiens,and Neanderthals.

So there was a lot of talk of a “missing link”—the biggest find in paleoanthropology since Lucy, the skeleton of a female Australopithecus, was excavated from a gully near Ethiopia’s Awash River in 1974. (Donald Johanson, the lead researcher in Lucy’s discovery team, founded the Institute of Human Origins, which later moved from Berkeley to Arizona State.)

Certainly, the discovery seemed destined to open a new chapter in the study of ancient hominids, kick the telegenic Berger into the firmament of paleo­an­thro­pological superstars, and likely pay off big time for the National Geographic Society, which funded Berger and made the diminutive H. naledi the cover story for the October issue of its magazine. Indeed, the find seems destined for the full Nat Geo multimedia treatment, including television specials.

Amid all the hoopla and confetti, however, a growing number of scientists are advising caution. They’re not denying the importance of the find; the fossils, they say, are invaluable. But they contend that the bones may not represent a new species. The evidence these skeptics point to suggests that the finds may actually be bones fromHomo erectus, the earliest known hominid to manifest the general proportions, stance and gait of modern humans. H. erectus had a long tenure on the planet, living from about 2 million to 70,000 years ago. The species was widely distributed (from Africa to East Asia and possibly southern Europe), used tools and fire, and may have constructed rafts to cross wide bodies of water.

By virtue of his scholarly bona fides, Berkeley paleoanthropologist Tim White seems the default, if somewhat reluctant, lead spokesman for the H. naledi contrarians. White worked with Richard Leakey in Kenya and Mary Leakey in Tanzania. In 1994, as a co-director of the Middle Awash Project in Ethiopia, White and his fellow researchers unearthed a fossilized partial female skeleton of Ardipithecus ramidus; at 4.4 million years of age, “Ardi” is the oldest know human antecedent. Two years later, White and his fellow researchers discovered fossils from Australopithecus garhi, a 2.5-million-year-old hominid who was contemporaneous with the earliest known use of stone tools.

And to White’s eye, Berger’s findings are probably South African representatives ofHomo erectus. The Homo naledi cranium is similar in conformation and size to the earliest and most primitive Homo erectus representatives, White said.

Berger maintains that 13 of the 83 characteristics he noted on H. naledi’s skull differ from characteristics on known H. erectus skulls. “But many of these 13 characteristics are also present in H. erectus, not absent [as Berger and his co-researchers] claim,” White said during a recent interview in his Berkeley lab. “I wrote a text on human osteology [the study of bones]. Also, I teach a class on [osteological] variation in humans. Many of the characteristics that [Berger and company] claim differentiate H. naledifrom H. erectus vary within our own species.”

Further, said White, some of Berger’s conclusions about H. erectus’s cranial features are just plain wrong. Berger maintains that an external occipital protuberance—basically, a bump at the back of the skull—is present in H. naledi but absent in H. erectus. White disputed this assertion by opening a cabinet in his lab, picking up a replica of an H. erectus skull found in Kenya, and pointing to a blatant occipital protuberance.

“That feature was noted in H. erectus fossils found in both [the former Soviet republic] Georgia and Kenya,” said White. “So you look at that, and you realize these claims of a new species are a little sketchy.”

Graphic from eLife commentary on a Berger team paper, illustrating differences between the skulls of homo species.

Graphic from eLife commentary on a Berger team paper, illustrating differences between the skulls of homo species.

Berger brushed off the criticism at a press conference near the findings. “Could this be the body of Homo erectus? Absolutely not. It could not be erectus,” he said.

Since then, White has cited other elements of the H. naledi saga that he finds troubling. The fossils come not from a single specimen, but from as many as 15 different individuals; it is therefore difficult to identify which bone came from which individual, and even whether they lived in the same period. Nor has Berger’s team been able to definitively establish the age of the bones. Photos taken of the find demonstrate to White that many of the fossils were not found in situ in rocky matrix, but had been “very disturbed, perhaps by earlier cavers, in the geologically recent past.”

“One tibia, for example, was white on one end, a clear indication it had been snapped off in the recent past,” said White. “This (region’s) complex is extensive and like Swiss cheese, and it’s a favorite with spelunkers. You find beer cans next to fossils that are 3.5 million years old. So it’s important not to jump to conclusions.”

Further, the excavation itself seems inadequate to justify Berger’s claims, White said. “It was about the size of a phone booth floor, roughly 80 x 80 cm and 20 cm deep,” White said. “That’s much smaller than you would expect for a discovery of this magnitude. Virtually all excavations related to important finds are much larger. With a typical excavation, you must establish a threshold that provides an understanding of the successive layers, that provides the means for comprehensive analysis and comparison with specimens from other sites.”

Finally, White observed, claims that the hominids might have buried their dead (because so many bones were found in the same chamber) were hyped heavily in publicity materials; but the scientific paper that Berger and his fellow researchers produced on the fossils is much more circumspect about such possibilities. “There is no evidence of burial rituals,” the Berkeley professor said. “The only evidence seems to be ‘We can’t think of anything else.’ This is not evidence.”

When California queried Berger on White’s comments on the discovery, he emailed the following response:

“I would really rather debate Tim’s ideas in a scientific journal where they belong rather than him attempting to debate this in the media. We have had almost 60 scientists working for two years on these refereed papers—Tim is shooting from the hip using characters that appear to largely concentrate on the head rather than the whole organism and well, the one thing I can assure you is the debate on Homo naledi being a ‘primitive Homo erectus,’ whatever that is, will not be settled in the media, either traditional or social. [Reporter’s note: The query was meant to imply an early representative of H. erectus, not a biologically ‘primitive’ form.] Tim continuing to use the media to argue whatever unsupported case he has for such assertions while protesting we are using media to ‘hype’ our fossils (although our ideas are in fact published in a well respected scientific journal) appears to be a way of just getting his name in the media rather than any form of scientific discourse. I would rather confine such discourse to where it belongs, a scientific paper published by Tim White in whatever journal he might be able to get such an argument in based on real numbers, real fossils and not just his opinion.”

The Academy can be a hothouse of discord and dissent, and some fields—paleoanthropology among them—seem particularly fertile ground for contention. But White is not alone in his uneasiness over H. naledi. Reviewers at top scientific journals also found the evidence for the new hominid species to be suspect. Berger and his team originally submitted multiple papers on H. naledi to the prestigious journal Nature,which rejected them.

Berger and his co-authors ultimately published their findings in eLife, an open-access, peer-reviewed, online journal edited by Cal biology professor and Nobel laureate Randy Schekman, the former editor-in-chief of the Proceedings of the National Academies of Science. Schekman assumed the editorship of eLife after declaring that he would no longer publish in closed-access journals such as Cell, Nature, andScience because the editors were more concerned with burnishing the reputations of their journals than publishing cutting-edge research. Like other open-access journals, eLife usually has a quicker peer-review process than long-established journals, and a much higher acceptance rate:around 25 percent, compared to the 7 percent acceptance rate of Science.

White said he agrees with Schekman that the peer-review process at the established journals is often flawed, but maintains that open-access journals such as eLife and PLOS One are not necessarily a panacea, in that research can be rushed to publication before being properly vetted by gimlet-eyed peers. “That’s clearly the case here [with H. naledi],” he said, noting the timeline between the discovery of the fossil site and the publication of the findings in the peer-reviewed and general press was only two years.

Indeed, the H. naledi announcement essentially was made simultaneously in the academic and popular media. During the press conference heralding the publication of Berger’s findings in eLife, a mock-up of National Geographic’s October magazine cover featuring the find was presented, and a television special sponsored by National Geographic and Pithecus was announced. By contrast, White and his colleagues took 15 years to publish their findings on “Ardi.” It took three years just to remove the fossils from the field. Years were spent carefully teasing the fossils from the matrix in the lab, obtaining moulds, photographs, and micro CT scans, compiling and analyzing the data, and comparing the fossils with all other known fossils and relevant living species.

Ultimately, findings on “Ardi” were published in both the journal Science and inNational Geographic; but White made sure the material appeared first in the peer-reviewed publication.

“We held the popular press off for 10 years,” says White, “for the simple reason that you can’t do good science when those guys are in the room. So when you actually invite them into the room—as Berger did, when they’re in the (tent) filming while excavation is going on, that has a very high impact on the work.”

Also, said White, Berger’s team was negligent in the handling and care of their find. He produced a photo of a member of Berger’s team scraping some of the bones; a small pile of shavings is clearly visible. “Those are bone scrapings, and that’s a terrible thing to see. You lose valuable information when you remove bone like that, information you’ll never be able to recover.”

Both Berger and National Geographic have run into hominid-associated controversy before. In 2008, Berger was the lead author of a paper in PLOS One on the discovery of the remains of dwarfish, Hobbit-like hominids in the Palau archipelago. They were reported to be similar to bones found earlier on the Indonesian island of Flores 2,000 kilometers to the south. The Flores find was tentatively identified as a new species, H. floresiensis, a designation that has since become highly controversial. Berger suggested that the Palau discovery indicated the Flores hominids may not constitute a separate species, but are rather a manifestation of the dwarfism that sometimes occurs among mammals isolated on islands.

But Berger’s hypothesis for a troupe of island-bound dwarves was quickly disparaged by many of his academic peers, who maintain the bones were more likely those of juvenile normal-sized humans. Michael Pietrusewsky, a University of Hawaii at Manoa anthropologist widely considered the preeminent authority on ancient South Pacific human remains, stated: “The more I read the paper, the more I am convinced it is complete nonsense and cannot be accepted as serious science.”

In a Nature piece on the Palauan discovery, reporter Rex Dalton described the controversy and Berger’s claims as a “crossfire between entertainment and science,” with entertainment winning. Dalton noted that Berger appears often on television, and that he and the National Geographic Society collaborated with a London production company, Parthenon Entertainment, to make a film of the Palauan finds.

Though National Geographic provides seed grants to scientists in an array of fields, many of whom produce valuable research, Dalton writes that “National Geographic is also a nonprofit media empire…. Its editors work to get featured discoveries by its funded researchers into both its flagship magazine and peer-reviewed journals at the same time. This arrangement can sometimes backfire, as it did in 2000 when the magazine featured a report of a flying dinosaur fossil that later turned out to be a cleverly faked composite. Berger’s project in Palau provides a behind-the-scenes view of when entertainment and science meet….” (Last month, National Geographicmagazine’s nonprofit parent organization effectively sold it to a for-profit operation whose chief shareholder is one of Rupert Murdoch’s global media companies.)

Berger, for his part, remains largely undaunted by the controversy his work has engendered. In response to misgivings over his Palau project, he emailed Nature’s editors: “Might it be that such critics have not read our manuscript as carefully as is required of a sophisticated debate on human variation before commenting?”

H. naledi—or whatever it is—certainly isn’t a modern-day Piltdown Man. White emphasizes that the discovery constitutes a major event in paleoanthropology. To illustrate his point during his recent interview with California, he produced another photo of one of Berger’s fossils. Even to an untrained eye, it was clear that it included digit bones.

“That’s a complete hand,” White said, calling these the first fossils ever found of a probable Homo erectus hand. “This find is remarkable enough for what it is—a huge injection of new data important for understanding early hominid evolution. There was no need to turn it into something more than that. Speculations about mortuary ritual or the need for a new metaphor to describe evolutionary process are both unnecessary and unwarranted.”

Source: UC Berkeley

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