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Homo naledi skeletal specimens by Lee Roger Berger research team

Homo naledi skeletal specimens by Lee Roger Berger research team [CC BY 4.0], via Wikimedia Commons

Paleoanthropology Wars: The discovery of Homo naledi has generated considerable controversy in this scientific discipline

News of the explosive discovery of Homo naledi in South Africa reverberated throughout the world in September 2015. The scientific, popular, and social media were equally abuzz with the truly breathtaking nature of the find: thousands of fossils, more than a dozen individuals, almost an entire skeleton reconstructed. Never in the 150-year history of paleoanthropology had so much been found at once. In one fell swoop, there are now more fossils of H. naledi than there are of more than half of the other named hominins that lived and died over the past seven million years. It was a one-of-a-kind discovery.

The find was different in another way as well. Lee Berger, the anthropologist leading the study, showed a staunch commitment to get the results of the team’s work, and the fossils themselves, out to the public as soon as possible. Within two years of their initial discovery, the first papers were published and the fossils were made available to the public, and not just in the traditional way of publishing a paper and placing precious fossils behind plate glass for the public to gawk at. Berger and another member of the team, John Hawks, completed extensive three-dimensional imaging of the fossils and provided the resulting data free of charge to anyone. With these data, one can 3D print your very own high-resolution casts of the original fossils. From anywhere in the world, one can obtain a facsimile of the highest possible quality, at no cost except for the materials for the printing. Even in our open-access era, this is an unheard of level of transparency and data sharing.

Despite this great excitement, it didn’t take long for some grumblings to be heard. Paleoanthropologist and National Academy of Science member Tim White, for example, stepped forward as the critic-in-chief. White has earned his place in the field’s hall of fame several times over and perhaps his biggest contribution is Ardi (Ardipithecus ramidus), one of the oldest known hominins. Nearly two million years older than “Lucy” (Australopithecus afarensis), Ardi brought deep insight into how and when the lineage that would give rise to humans diverged from our common ancestor with apes.

White’s criticism of the Homo naledi is both of process and result. First and foremost, White has expressed extreme annoyance with how quickly Berger and his team revealed their findings and announced their conclusions. In his view, the proper place to announce fossils is a scientific conference, where their importance can be debated by the experts before engaging the public. He used the example of Ardi to make his point, noting that 15 years passed before the initial discovery of the fossils in 1994 and the first scientific paper about them in 2009. In the intervening years, preliminary measurements were announced at many scientific conferences, many voices were heard, and the final interpretation was a team effort of the brightest and most experienced minds in the field.

While it seems hard to argue with White’s position that slow, careful, deliberative science yields the most trustworthy conclusions, there is a dark side to one person holding such precious fossils close to his vest for so long: the accusation of elitism. During the many years that everyone in the field knew that White had in his possession the bones of an incredibly ancient hominin, he had complete control over who had access to them and how much could be revealed. In addition to bolstering his own fame in the field, the protracted protectionism of the Ardi fossils meant that the pace of research thereof was totally under his control.

Berger and Hawks hold a different view: fossils do not belong to, and should not be controlled by, any one person. They are precious gifts from our past and the property of the whole world. To guard and conceal them is tantamount to theft. This is a new way of doing science and the benefits are obvious and profound.

White’s criticism goes further and gets even more pointed. White does not feel that Homo naledi is a new species at all and is instead a smaller and more primitive variant of the well known Homo erectus. In an interview entitled, “Some Bones to Pick,” White levels his damning charges: “These are a small, primitive H. erectus… This is because they are not biologically different, in any significant way, from already known H. erectus… Of the 80+ traits listed in the e-LIFE supplemental material, only a small fraction of them are even claimed to differentiate these fossils from earlier described H. erectus, and that fraction of characters is known to vary among members of the same species (even population) of both H. erectus and H. sapiens. In other words, the newly described ‘species’ is an example of artificial species inflation in palaeoanthropology.”

Although White is known for being soft-spoken and mild-mannered, those are fighting words. Not long after the first article appeared, California Magazine, published by the Alumni Association of the University of California at Berkeley where White is the University Professor of Paleoanthropology, interviewed him for a follow-up article. He continued with his discussion of the overlap of some anatomical features between the two species and concluded, “these claims of a new species are a little sketchy.”

Hawks, second-in-command of Berger’s naledi team, responded swiftly on his blog, easily the most widely read blog on paleoanthropology. He detailed a half-dozen or more major differences between naledi and erectus. H. naledi has a substantially smaller cranial capacity, a thinner mandible, and a more flattened femur neck than erectus. He also notes differences in the scapula, tibia, pelvis, vertebrae, and several aspects of dentition between naledi and erectus and in all cases, the differences are so stark that there is complete or nearly complete non-overlap in the ranges found for these measures.

Hawks states it clearly, “It’s just a poor match to H. erectus, so that the only way to make the H. naledi fossils fit within Homo erectus is to stretch that species beyond any other ever defined in the human lineage.” Ouch.

This fight may be larger than a simple disagreement regarding the features of H. naledi. We could be witnessing a transition in paleoanthropology and the passing of the torch from the Old Guard to a new generation with a new take on how the field should advance. It’s not just about making fossils available or not; it’s about how the information in those fossils should be interpreted. Where White sees rich variation within a single widely dispersed and long-lived species, others see many individual species with a mosaic of shared and unique characters.

Through random mutation, evolution is relentlessly tinkering with the animal body plan, driving species toward diversification and various modes of living. The result is often a wide and bushy family tree that is trimmed and culled by the harshness of natural selection. Among the best examples of this among primates are the lemurs of Madagascar. While being geographically isolated for tens of millions of years, they diversified intensely, evolving into dozens of species with widely variant lifestyles and anatomy. If the many hominin species had flourished for a longer time period, we might have seen as much diversity within Homo and other related genera as we do among the sifakas and other lemurs of Madagascar.

As Ian Tattersall wrote in his recent book about the 20th century development of the field of paleoanthropology, many of the early powerful figures in the field had little or no training in evolutionary theory. They were mostly anatomists and had no basis for understanding how morphology can be used to understand evolutionary relationships. Each new fossil was a new species and that was that.

However, in came Ernst Mayr, who knew little about primates or hominids, but was an authority on evolution and systematics due to his work on the speciation of birds. His influence on paleoanthropology was to usher in the era of extreme lumping, convincing everyone that the entire human fossil record was one lineage and just three species, each turning into the other until we reach Homo sapiens. Echoes of that type of extreme lumping can be found in Tim White’s criticism of H. naledi, who similarly criticized the discovery of Australopithecus deyiremeda earlier this year, insisting that it was no more than a variant of A. afarensis, the species of Lucy.

I spoke with Ian Tattersall and asked his opinion of the controversy. While he was loathe to criticize colleagues whom he greatly respects, he did admit that “Tim’s definition of erectus is so broad so as to make that sort of thing inevitable.” When I asked for his opinion, he said “I don’t think there’s any chance this is erectus. It had a very small brain, but some surprisingly modern features to accompany that tiny brain.”

For his part, Tattersall seems to be on the complete opposite end of the spectrum as White. “On top of that, I don’t believe that erectus was in Africa at all, so we’re not going to see eye-to-eye on that one. But I think White’s main complaint is that Berger made everything public so quickly.”

Asked where he stands on the matter of quick, open-access publishing, Tattersall was unequivocal, “Well this certainly sets an incredible precedent for the future in terms of openness and making things accessible and I think this is a very good move.” For an elder statesman of the field, Tattersall sure likes the new trends.

Tattersall also described White as “the ultimate traditionalist.” Although he denies it, it is hard not to see that label as a stinging rebuke given the thrust of Tattersall’s latest book. But I dare not twist his words. His respect for White was obvious.

For his part, Berger struck back immediately. In the same California Magazine article, he says, “The debate on Homo naledi being a ‘primitive Homo erectus,’ whatever that is, will not be settled in the media, either traditional or social. [White] 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.”

Instead, Berger invites White to submit his challenge in the scholarly literature and let the community of experts sort it out. He continued, “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.”

To dig a little deeper, I spoke with Professor Berger myself. I hadn’t even completed my first question when he said, “I don’t know why [White] would say that. He seems to be going just on anatomy and if you do that, we probably haven’t gone far enough!” Berger began to rattle off a list of anatomical differences between H. naledi and H. erectus before musing, “You know, [paleoanthropology] is a very public field and these things play out in the spotlight with big personalities and it’s clear that some of the arguments, particularly those raised in the media, have nothing to do with the science.”

I raised the question of whether White’s concerns actually stem from a much larger disagreement, that is, whether the entire human fossil record can be reduced to just a few species, each transforming into the other. Berger agreed but lashed out again, “I would further add that what he says and what he does are two different things. White does talk that way about other people’s fossils, but everything he finds is a new species.”

Taken aback, I asked if I could quote him on that. “Yeah, sure. I mean he takes tiny fragments like garhi [Australopithecus garhi]… and calls it a new species. He published a new genus in an erratum! Actions speak louder than words.”

Hawks echoed this criticism in his blog, stating that White, “has no time for species that he himself has not named.”

When I asked Berger where he stood in the disagreements about a rich variety of speciation among hominins versus a skinny family tree slowly evolving into H. sapiens, he clearly came down on Tattersall’s side, “What naledi and Homo sediba have clearly shown us is that there must have been some adaptive radiation.”

However, Berger advises caution on the matter. “Historically, paleoanthropology has been a field of fragments. What the complete skeletons are showing us is that [using] specific small parts of anatomy, like a jaw or some dentition or even a cranium, to make conclusions about other parts or about the whole body can be very misleading.”

I asked, “Because these species end up being mosaics of features found in other species?” He responded, “Exactly, yeah.”

Berger continued, “There are two possible scenarios. One, and I think this is the more logical one, is that if we could obtain a complete fossil record, we would see a lot of adaptive radiation. There is the possibility that we have misled ourselves on that based on a very fragmentary record. I don’t think so, however. Both naledi and sediba point to it being less likely. I think we have seen a large number of experiments [with anatomy and lifestyle] taking place over all this time.”

If something is not Australopithecus, it’s Homo. If it’s not Homo, it’s Australopithecus. Maybe it’s time for us to stop stuffing new morphologies into the old pigeonholes we’ve had for a hundred years.

Berger also took issue with how many paleoanthropologists, particularly in the U.S., place undue weight on the age of fossils instead of the phylogeny. “You don’t necessarily need to know how old something is to know how it relates to something else. There’s a trend in paleoanthropology over the last 40 years that says if you have the date for something, you know what it is. This only makes sense if only one hominid species existed at any one time.” Therein is the rub.

Because White has insisted that naledi is actually erectus, I asked if the dating of naledi would help resolve this. Berger demurred, “I think he would say that he already knows how old it is! [laughs.] He could tell you the date since it’s Homo erectus!”

I couldn’t resist probing for some unpublished results regarding the date, but Berger wasn’t ready to talk about that yet. “I have ordered four independent methods of dating before we come out with an age because, while the questions we were asking in the first phase didn’t require a date, there are other questions that need to be addressed where dating is important, such as the matter of the potential grave burial. Therefore I don’t want to make the mistake that others have made by releasing a date that is not the best we can do. We’ve seen the results of that in the fights that erupted in the past, which can be very destructive.”

Another matter dividing the paleoanthropology community is the need to revise the Homo genus, which suffers from poor boundaries and vague defining characteristics. As I’ve written previously, the discovery of H. naledi highlights this perfectly. I asked Berger if he agreed it was time to revise Homo, “Oh yeah, and we’re working on that as well. We were right in the center of that argument with sediba and again with naledi where half the field said you should have put in Homo and half the field said you should have put it in Australopithecus. The irony of this!”

Tattersall bemoaned this as well. “Because they found a brow ridge in some of the crania [of naledi] and you don’t see brow ridges in Australopithecus, it had to be Homo. That’s pretty much how it works. If something is not Australopithecus, it’s Homo. If it’s not Homo, it’s Australopithecus. Maybe it’s time for us to stop stuffing new morphologies into the old pigeonholes we’ve had for a hundred years.”

I asked if Berger thought that naledi would probably end up in a new genus if Homo is revised. “You know, I don’t know where things will end up if we ever reach a new synthesis. We probably need more fossils to really do that, more skeletons especially.”

That’s one point every single paleoanthropologist can agree on. We need more fossils. END

About the Author

Nathan H. Lents is Professor and Director of the Cell and Molecular Biology program at John Jay College of The City University of New York. His new book, Not So Different: Finding Human Nature in Animals will be published in the summer of 2016 by Columbia University Press. He also maintains The Human Evolution Blog and is a free-lance writer on various topics that interest him. He can sometime be found on Twitter and Tumblr.

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