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The following article was originally published here on January 29, 2018.
It looks like paleoanthropologists will not get much relief from the 2017 annus horribilis (Bechly 2017) in the new year. Two big stories have already hit the news in January.
First, on January 22, Nature News (Callaway 2018a) and John Hawks (2018) reported about and commented on the apparent suppression of scientific evidence that may refute the interpretation of Sahelanthropus as the oldest bipedal hominin.
On the morning of July 19, 2001, French scientist Alain Beauvilain and three Chadian colleagues discovered a fossil cranium in the dunes of the Chadian Sahara Desert, together with an assemblage of other fossils. The sensational discovery was covered by worldwide media, and the discoverer wrote a popular science book (Beauvilain 2003) about the story of the find. The specimen was nicknamed “Toumaï” (or, “hope of life”) in a press release from the University of Poitiers in 2002. It was shortly thereafter described by the head of the research team, Michel Brunet (Brunet et al. 2002), as the fossil hominin Sahelanthropus tchadensis. Geological and paleontological evidence (Vignaud et al. 2002) as well as radiometric dating (Lebatard et al. 2008) suggested that this fossil was between 6.8 and 7.2 million years old and therefore would represent the oldest known ancestor of humans. The smashed fossil thus achieved iconic status. The dating is still a bit dubious because the skull was not found in situ in Miocene deposits (Beauvilain 2008). Beauvilain & Watté (2009) even speculated that modern nomads might have assembled the bones and placed them in a grave in the sand dunes, without being aware that they are fossils. Later native Muslim camel herders could have reoriented the exposed skull towards Mecca and reburied the specimen until it was again uncovered by the wind and discovered by science in 2001. Even though the evidence for this speculation is weak (Hawks 2009a), the circumstances of this famous fossil’s discovery are certainly far from optimal.
The fossil skull is also poorly preserved and was totally battered, which made interpretation cumbersome and highly ambiguous. A computer-aided 3D reconstruction by Zollikofer et al. (2005) attempted to establish the crucial position of the foramen magnum as evidence of bipedal locomotion, but this remains controversial (Wolpoff et al. 2006). Immediately after the original description by Brunet et al. (2002), writing in the journal Nature, a scientific dispute erupted between the describer (Brunet 2002, Guy et al. 2006) and other proponents of a hominin attribution (Begun 2004), on the one side, and critics on the other side (Wolpoff et al. 2002, 2006). The latter strongly doubted the evidence for bipedalism and considered the cranium as belonging, instead, to an extinct ape, possibly a female gorilla. Various critical authors also remarked that Sahelanthropus is too old to belong in the human lineage, based on molecular clock estimates of the chimp-human split.
As an interesting side note, a few years ago an evolutionist friend of mine pointed out (E. Weber, personal communication) that within a Darwinian paradigm the “Sahelanthropus as gorilla-ancestor hypothesis” would also fit nicely with well-established African biogeographical patterns (as suggested by the zoologist Jonathan Kingdon), because the origin of the gorilla versus chimp+Homo lineages would align well with a North versus South splitting event, while the origin of the chimp and Homo lineages would follow a West (rainforest) versus East (savanna) pattern. I have never encountered this argument in the published literature on Sahelanthropus, maybe because few paleoanthropologists are well versed in African mammal biogeography.
A still little-known fact is that a hominid mandible (Brunet et al. 2005) and left femur were found closely associated with the cranium of Sahelanthropus on the day of its discovery. Strangely, in their paper offering further details about fossils attributed to Sahelanthropus, Beauvilain and Le Guellec (2004) did not mention this femur. Beauvilain and Watté (2009) mention the mandible and femur, and feature overview photos of the findings at the site, but provide no detailed description, photos, or drawings of the femur. Otherwise, the femur was only mentioned in a blog post by paleoanthropologist John Hawks (2009b) and featured on an anonymous website about Sahelanthropus (Anonymous). When John Hawks inquired with the original describer of Sahelanthropus, Professor Michel Brunet, he received the following remarkable reply:
In Chad, we have uncovered thousands of bones, which are in the process of study. Perhaps among them are hominid bones, but I only comment on those that have been published in a scientific review.
This is plainly false, because in fact only a few dozen fossils were uncovered together with the cranium of Sahelanthropus. This is clearly visible in the photos from the discovery site (Hawks 2009b). Hawks comments that the femur bone lay unrecognized for three years in the Toros-Menalla faunal collection but was recognized as a hominid femur in 2004.
Now, Callaway (2018a) reports in Nature News, in the words of Hawks (2018), that
two scientists, Roberto Macchiarelli and Aude Bergeret, attempted to present a talk describing this femur at the annual meeting of the Societé d’Anthropologie de Paris this month. The society rejected their abstract, which has triggered some professional criticism.
Callaway quotes paleoanthropologist Bill Jungers at Stony Brook University as saying that the description of the femur is “long overdue” and “We don’t know why it’s been kept secret. Maybe it’s not even a hominin.” On his blog, John Hawks (2018) spells out the significance:
If a femoral specimen was found with the Sahelanthropus cranial remains, it is important evidence. If the femur preserves anatomy that would test the hypothesis of upright posture or bipedal locomotion, no one should pretend that the evidence does not exist. Secrecy was ridiculous from the start, now it is inexcusable.
Hawks also says:
What amazes me is just how long this has all gone on. All of the critics could be silenced within hours by data and evidence. Instead, silence about these key fossils has reigned for fifteen years.
He mentions that David Pilbeam, who was a co-author of the original description, had already seen the femur a decade ago. Hawks finds this “very troubling” and calls for “Nature‘s editors to investigate.” Indeed, I think the reasons for this secrecy are pretty obvious, and I personally consider this case a genuine scientific scandal. Of course, the discovery of the oldest fossil hominin makes for better publicity and yields higher funding than the discovery of just another fossil ape. The association of the skull with a hominid femur that does not seem to be hominin, but, instead, more similar to the femur of a quadrupedal ape (Macchiarelli and Bergeret quoted in Callaway 2018a and Hawks 2018), was certainly inconvenient. Scientists are only human, though, and what moves them may not always be a purely unbiased pursuit of the truth. In an idolized discipline such as paleoanthropology, a great booster of scientific careers and fame, the incentive to see the evidence as one wishes may be even greater than in other, less celebrated fields. Indeed, Michel Brunet, the describer of Sahelanthropus, became famous in France and had a street named after him in Poitiers. If nothing else, this case shows that in evaluating alleged proofs of human evolution, a healthy dose of skepticism is called for.
…And Another Rewrite
Just three days after the Sahelanthropus scandal, more bad news for the standard narrative of human origins came along. This arrived on January 25 with a new scientific publication by Hershkovitz et al. (2018) in the journal Science, again reported by Callaway (2018b) in Nature News.
The authors of this new study describe a re-dating of a modern human jaw discovered in 2001 in the Misliya cave at Mount Carmel in Israel. After a very careful re-evaluation, using different high-tech methods, the large team of researchers confirmed the attribution to modern Homo sapiens. However, they arrived at a surprising and solid new dating for this specimen at between 177,000 and 194,000 years before the present, which makes it the oldest evidence for modern humans outside of Africa. The problem is, that the standard narrative maintained that modern human originated about 200,000 years ago in Northeast Africa and only much later (about between 60,000 and 70,000 years ago) left Africa to spread around the globe (Callaway 2018b). Single discoveries of modern humans in the Levant before this time, like the 80,000-120,000-year-old remains from Skhul cave and Qafzeh in Israel, were considered to be failed early attempts to leave Africa that left no later descendants. The new results and other recent findings show that such ad hoc hypotheses to explain away conflicting evidence are no longer tenable. That is why the Times of Israel cites Professor Israel Hershkovitz as saying, “This has changed the whole concept of modern human evolution…The entire narrative of the evolution of Homo sapiens must be pushed back by at least 100,000-200,000 years.” The author of the article comments, “With this Misliya cave jawbone, however, the history of human evolution is being rewritten” (Borschel-Dan 2018, emphasis added).
Where have we heard that before? Dienekes Pontikos (2018), who hosts one of the most popular paleoanthropological blogs, notes the new results with the headline, “Out of Africa: a theory in crisis,” and remarks that it “should cause a rethink of the currently held Out-of-Africa orthodoxy.” Hear, hear!
- Anonymous. “Sahelanthropus tchadensis, Toumaï, Skull and Femur.”
- Beauvilain A 2003. Toumaï, l’aventure humaine. La Table Ronde, Paris, 239 pp.
- Beauvilain A, Le Guellec Y 2004. “Further details concerning fossils attributed to Sahelanthropus tchadensis (Toumaï).” South African Journal of Science 100: 142–144 (PDF).
- Beauvilain A 2008. “The contexts of discovery of Australopithecus bahrelghazali (Abel) and of Sahelanthropus tchadensis (Toumaï): unearthed, embedded in sandstone, or surface collected?“ South African Journal of Science 104 (5/6): 165–168.
- Beauvilain A, Watté J-P 2009. “Was Toumaï (Sahelanthropus tchadensis) buried?“ Anthropologie XLVII(1-2): 1–6 (PDF).
- Bechly G 2017. “Fossil Footprints from Crete Deepen Controversy on Human Origins.” Evolution News, September 6, 2017.
- Begun DR 2004. “The Earliest Hominins — Is Less More?“ Science 303: 1478–1480.
- Borschel-Dan A 2018. “Jawbone fossil found in Israeli cave resets clock for modern human evolution.” Times of Israel, January 25, 2018.
- Brunet M et al. 2002. “A new hominid from the Upper Miocene of Chad, Central Africa.” Nature 418: 145–151.
- Brunet M 2002, Reply to: “Sahelanthropus or ‘Sahelpithecus’?“ Nature 419: 582.
- Brunet M, Guy F, Pilbeam D, Lieberman DE, Likius A, Mackaye HT, Ponce de León MS, Zollikofer CPE, Vignaud P 2005. “New material of the earliest hominid from the Upper Miocene of Chad.” Nature 434: 752-755.
- Callaway E 2018a. “Controversial femur could belong to human relative.” Nature News, January 22, 2018.
- Callaway E 2018b. “Israeli fossils are the oldest modern humans ever found outside of Africa.” Nature News, January 25, 2018.
- Guy F, Lieberman DE, Pilbeam D, Ponce de Leon M, Likius A, Mackaye HT, Vignaud P, Zollikofer CPE, Brunet M 2006. “Morphological affinities of the Sahelanthropus tchadensis (Late Miocene hominid from Chad) cranium.” Proceedings of the National Academy of Sciences, USA 102: 18836–18841.
- Hawks J 2009a. “Sahelanthropus: Did camelherders bury Toumaï facing Mecca?“ john hawks weblog, May 18, 2009.
- Hawks J 2009b. “Sahelanthropus: ‘The femur of Toumaï?’“ john hawks weblog, July 3, 2009.
- Hawks J 2018. “What’s the deal with the Sahelanthropus femur?“ john hawks weblog, January 22, 2018.
- Hershkovitz I et al. 2018. “The earliest modern humans outside Africa.” Science 359(6374): 456–459.
- Lebatard A-E, Bourlès DL, Duringer P, Jolivet M, Braucher R, Carcaillet J, Schuster M, Arnaud N, Monié P, Lihoreau F, MacKaye HT, Vignaud P., Brunet M, 2008. “Cosmogenic nuclide dating of Sahelanthropus tchadensis and Australopithecus bahrelghazali: Mio-Pliocene hominids from Chad.” Proceedings of the National Academy of Sciences, USA 105(9): 3226–3231.
- Pontikos D 2018. “Out of Africa: a theory in crisis.” Dienekes Anthropology Blog, January 26, 2018.
- Vignaud P et al. 2002. “Geology and paleontology of the Upper Miocene Toros-Menalla hominid locality, Djurab Desert, Northern Chad.” Nature 418: 152–155.
- Wolpoff M, Senut B, Pickford M, Hawks J 2002. “Palaeoanthropology (communication arising): Sahelanthropus or ‘Sahelpithecus’?“ Nature 419: 581–582.
- Wolpoff M, Hawks J, Senut B, Pickford M, Ahern J 2006. “An Ape or the Ape: Is the Toumaï Cranium TM 266 a Hominid?“ PaleoAnthropology 2006: 36–50.
- Zollikofer CPE, Ponce De León MS, Lieberman DE, Guy F, Pilbeam D, Likius A, Mackaye HT, Vignaud P, Brunet M 2005. “Virtual cranial reconstruction of Sahelanthropus tchadensis.” Nature 434: 755–759.