We’re discussing a new paper in Science Advances that claims to find clear evidence of bipedality in the species Sahelanthropus tchadensis. As we saw in an initial post, there remain many scientific critics of the view that Sahelanthropus tchadensis was a habitual biped, and this debate is far from over. As we saw, Roberto Macchiarelli, is a paleoanthropologist who co-wrote two scientific papers published in the Journal of Human Evolution that were critical of the view that Sahelanthropus was a biped. He recently told the Washington Post the following:
“Body proportions in Sahelanthropus are 100 percent apelike, certainly not ape-hominin ‘intermediate,’” Macchiarelli said in an email. “Compared to most scientific disciplines and research,” he added, “paleoanthropology is deeply affected by competition and politics.”
Another story about the new the paper, this one in The Guardian, reports “Fresh bone analysis makes case for earliest ‘ancestor of humankind’, but doubts remain.” It closes with an intriguing quote from the new paper’s lead author, Scott Williams, a paleoanthropologist at NYU, about the current state of the evidence:
Dr Guillaume Daver and Dr Franck Guy at the University of Poitiers, who have long argued that Sahelanthropus was bipedal, welcomed the new evidence, but said the debate would not be settled without more fossils, which they hope to find when the Chadian-French team return to the site this year. That appears to be something everyone agrees on. “I think it’s a case of too few fossils and too many researchers,” said Williams.
This reminds me of another pithy quote from Jerry Coyne who wrote in Why Evolution Is True that “palaeoanthropology is a field in which the students far outnumber the objects of study” (p. 197). But there are good reasons to understand that some people might not want critics like Macchiarelli studying the fossil.
“Too Many Researchers”?
Professor Williams’s quote is fair, but one could interpret it in different ways. On the one hand, yes, everyone agrees that more fossils are needed. But could the quote also lend itself to a darker interpretation that there should be fewer researchers studying this specimen?
I don’t know for sure that Williams necessarily intended to be taken that way. But I do know that there have been rumors that some of the original discoverers of Sahelanthropus tchadensis, or “Toumaï” — who wanted to see it as a bipedal human ancestor — may have made it difficult for other competing researchers (including Roberto Macchiarelli’s team!) to get access to the bones so they could make their own independent assessments. I covered this back in 2021 based upon a New Scientist story that hinted at such disturbing behind-the-scenes shenanigans. Roberto Macchiarelli probably had something like this in mind when he cited the “competition and politics” in paleoanthropology.
Indeed, the “bitter” feelings underlying these disputes were elaborated last year in a 2025 article in The Guardian titled “The curse of Toumaï: an ancient skull, a disputed femur and a bitter feud over humanity’s origins.” The article opened by stating:
When fossilised remains were discovered in the Djurab desert in 2001, they were hailed as radically rewriting the history of our species. But not everyone was convinced — and the bitter argument that followed has consumed the lives of scholars ever since.
You can read the article to get the full story, but to summarize, in 2004 Macchiarelli was shown the femur of Toumaï by a graduate student. The student was apparently just looking for help identifying bones while her advisor was gone, but by showing the Toumaï femur to Macchiarelli, she unwittingly stepped into a big mess. The student ultimately ended up taking the fall for allegedly “leaking” information about this very important bone to someone outside of Michael Brunet’s team. According to the story, “The laboratory seemed to close ranks against her, she said, and after her master’s she was made to understand there was no support for her to take a doctorate.” It further recounts a chilling tale of what the student was told:
At one point, however, [the student] said, one of her advisers appeared with the femur in his hand. “This piece,” he warned, holding it before her: “You forget you ever saw it.”
It seemed like lots of people wanted to forget about the femur, because years went by and nothing was published about the bone. According to the 2025 article, Macchiarelli had concerns that Brunet hid the femur of Toumaï from other researchers because it did not support his claims of bipedalism in Sahelanthropus tchadensis:
None of Brunet’s papers contained any reference to a recently discovered Sahelanthropus femur, however, and if one read closely, Macchiarelli realised, many of them seemed to implicitly deny its existence. A 2004 journal article reported an “absence of limb bone remains”. The following year, in Nature, Brunet wrote that “several lines of evidence” suggested that Sahelanthropus was bipedal, with the proviso that, in order to be certain, “postcranial evidence will be necessary”; he declined to report that he was now in possession of precisely such evidence. Macchiarelli at one point sent a long letter to the president of the University of Poitiers and several top officials at the CNRS, France’s prestigious research network, in order to “formally accuse” Brunet of lying about what he called “the femur affair”; nothing came of it. “There’s been a selection, a choosing of which remains to publish, and which not,” Macchiarelli told me. “No one has the right to do that!”
[…]
Macchiarelli had initially assumed that Brunet was keeping silent about the femur for essentially emotional reasons, out of shame for not having been there for its discovery in the desert in 2001, and for not having recognised it afterward. By now, however, he had come to suspect that Brunet was in fact hiding it “because it didn’t fit”, he said – because it seemed to show that Sahelanthropus was not a biped, and presumably not a hominin at all, and because Brunet’s reputation would be shattered if anyone found out.
Meanwhile Macchiarelli was cut off from Brunet’s research team at the University of Poitiers:
Macchiarelli made overtures of reconciliation to the colleagues who felt him a traitor, he said, including a letter hoping for “a return to serenity”. But it didn’t work. Brunet’s group behaved “like a tribe, like a closed-off family”, he told me, like a “cult”. Brunet ought to have thanked him for bringing an important fossil to his attention, Macchiarelli thought. Instead, he urged administrators not to renew Macchiarelli’s contract. Macchiarelli’s office was relocated; he was forced to clean and supply it on his own, he said, and to buy his own stamps, printer cartridges and toilet paper. Though he remained a professor of the University of Poitiers, he took a research position in Paris. “I was attacked, I was insulted, I was threatened,” he said, of his time in Brunet’s group.
There’s a lot of additional detail, colorful language, and back and forth in the story, which I recommend reading if you want to know more. But this backstory provides a lot of context for Macchiarelli’s recent comment in the Washington Post that “paleoanthropology is deeply affected by competition and politics.” Whatever Scott Williams intended in saying there are “too many” Toumaï researchers, it does indeed seem that over the years the custodians of this fossil have tried to exclude certain mainstream researchers from having access to the bones.
Strong Language
And then there’s even evidence of competition and politics in this recent technical paper in Science Advances. The 2025 article about Sahelanthropus in The Guardian notes that in 2024, Macchiarelli along with Clément Zanolli and other colleagues published an article in the Journal of Human Evolution (JHE) which further critiqued the view that Sahelanthropus is bipedal:
Last year, in the JHE, Macchiarelli published a response, reaching conclusions that were precisely the inverse. When I spoke with his co-author Clément Zanolli, he offered a wry compromise with the findings of the Nature paper. “It’s not impossible that Sahelanthropus could have used bipedalism,” Zanolli, a CNRS researcher and former student of Machiarelli, told me. “Just like chimpanzees do occasionally today.”
The new paper by Williams et al. in Science Advances comments on that 2024 JHE paper in a section that provides a fascinating review of the debate over locomotion in Sahelanthropus. The review is fascinating not only because it notes the highly divergent views published in the literature but also because it uses language that, for a scientific paper, is pretty strong and seemingly has an edge to it.
Williams et al.’s review describes the pro-bipedalism papers as providing the “official description” of Sahelanthropus, almost as if that “official description” ought not be questioned. Again using similar “official” language, Williams et al. identify a pro-bipedalism paper published in 2022 as the “official publication” and complain that “A separate team” — which would again be Macchiarelli’s team — “published images and initial analyses of the femur (30) before the official publication in Nature by Daver et al.”
Here’s what I want to know: Since when is one paper the “official publication” and a different paper, also published in a well-respected journal, less than “official”?
Also oddly, in two instances when describing the publications from Macchiarelli and colleagues, Williams et al. allege that the critics “dismissed” the evidence for bipedalism in Sahelanthropus tchadensis. Yet Macchiarelli’s and his team provided their own fact-based analysis. This repeated use of the word “dismissed” in a scientific paper again has an accusatory edge that seems to insinuate that the critics’ analysis was somehow unfair and substandard.
Undoubtedly the strong language derives from some hard feelings here, and possibly a less-than-objective agenda.
A “Vicious” and “Disputatious” Field
One thing I appreciated about the 2025 Guardian article on Sahelanthropus is that it brings out the human side of the story, calling palaeoanthropology “a notoriously disputatious, not to say vicious, field.” The article then comments on the reasons for these disputes — stemming from both the lack of fossils and the nature of the subject matter:
[M]ost of the fighting in palaeoanthropology is simply a function of the wild imbalance between the number of palaeoanthropologists, which is large, and the number of objects available for them to study, which is very much not. Our direct knowledge of the first few million years of human evolution derives from a collection of bone fragments that could no more than halfway fill a large shoebox. “It’s a bit frustrating,” the researcher Jean-Jacques Jaeger told me, with some understatement, “but there really is a gap in the palaeontological record between, I’d say, 14m and 5m years ago in Africa.” Among other things, the tectonics of this period were not conducive to fossil formation. Unfortunately, this period is precisely when the human line began.”
Still, the greatest conflicts in the field tend not to be over access to fossils but over the sense one makes of them. Attempting to reconstruct the history of early humanity from the available evidence is, it has been said, akin to trying to divine the plot of War and Peace from just 13 of its pages, picked at random. Major disagreements of interpretation are inevitable, as are major errors, and the discovery of a single new “page” can change everything we thought we understood about the broader story. What we call our knowledge of the deep human past is in fact overwhelmingly provisional, contingent upon whatever fossil happens to turn up next.
[…]
If logic were the only factor, the flimsiness of our understanding would inspire restraint, and new fossil discoveries would only rarely give rise to grand pronouncements about the nature of humanity. But the impulse to make such pronouncements, heightened by the prospect of fame, not to mention grant money, can be overwhelming. There is a large and receptive audience for stories about the origins of humankind, however conjectural the stories may actually be. We yearn to know how and why we came to be ourselves, how humanity emerged out of nature. Frequently we yearn, as any historian of the prehistoric sciences will tell you, to the point of unreason.
So this is where Sahelanthropus leaves us: Paleoanthropology is a “vicious” and “disputatious” field full of “competition and politics” with “too many researchers” and “too few fossils.” It studies a topic of the utmost importance — “the origin of humankind” — where big discoveries can reward you with “fame” and “money.” It’s always appropriate to express the hope that more fossils will be found to settle these debates, but at the very least we should exercise sobriety and caution before accepting the claims of this field carte blanch — especially when evaluating media proclamations of a new “human ancestor.”
I’ll give the last word to The Guardian, which expresses pessimism that some of these debates will ever be settled:
If Sahelanthropus is indeed a hominin, statistics all but rule out the possibility that it is an actual human ancestor. … We will almost certainly never find fossils from that ancestor, and in truth we wouldn’t know it if we did. We could one day hold in our hands the remains of the literal ur-mother, the individual animal that birthed the whole of human history. There is no technology, extant or imaginable, that could extract that marvellous secret from her bones.