Africa

Some weeks ago, I wrote about an article by Alain Beauvilain and Jean-Pierre Watté, in my post, "Sahelanthropus: Did camelherders bury Toumaï facing Mecca?" If you missed that post, go back and read it -- it gives some essential background.

I ended the post with this little observation:

Toumaï's skull was found alongside a femur.

I imagine that a majority of paleoanthropologists have heard that the faunal collection from Toros-Menalla includes a primate femur of the right approximate size to match the Toumaï skull. Probably only very few knew that this femur may have been found in the immediate locality of the skull. Still, a lot of them must be wondering: If there are possible postcranial remains of Sahelanthropus, wouldn't they be the most important test of whether the species is the first hominid?

Now, thanks to a story in the July print issue of the French science magazine La Recherche, along with some valued correspondence from readers, it's possible for me to give some more details.

The La Recherche story, reported by Nicolas Constans, includes a quote from Aude Bergeret, a former student at Poitiers, and now director of the Musée de la Haute-Auvergne. I want to give my translation of the story's first two paragraphs, which pose the obvious question:

The femur of Toumaï

Eight years after the discovery of the skull of the oldest known hominid, an unedited photo shows that a femur of the same species was found simultaneously. Why hasn't it been published?

The skull of Toumaï is considered by many paleontologists as that of the oldest known hominid, Sahelanthropus tchadensis. The position of the hole connecting its vertebral column indicates that it was probably a biped. But to know how it walked would require one of the bones of the leg. Unfortunately, none were found at the site, as stated in 2002 by the CNRS. However, a photograph from the day of the discovery has now been published in a Normandy review (pictured above). It shows the skull posed on the sand next to a bone, designated as the femur of a hominid. What many paleontologists privately confided for several years is from now on in the public square. Why did this announcement not follow the normal publication channels?

Well, this may not be such a mystery. We all know that there's no urgency whatsoever in the publication of early hominid remains. Fifteen, twenty years, however long it takes for preparation and analysis, it's no problem. Hey, just look what happens when you publish your early hominid femur quickly, complete with CT scans, like the Lukeino hominids. You get all kinds of sniping from other early hominid excavators, about how you really did everything wrong and can't even read a CT. It's a wonder any of them are willing to publish anything at all.

Still, the story in this case took several interesting turns. Some of them were detailed in my earlier post on the paper by Beauvilain and Watté. Those have to do with the discovery itself and alleged inaccuracies in subsequent descriptions of the discovery in scientific journals.

A different twist to the story is what happened after the discovery, during the study of the faunal remains in Poitiers. The femur figures into the story of the discovery, because Beauvilain's pictures put it at the scene. But it is in other respects a separate issue, and I don't think it helps to confuse them with each other.

The femur

Here are two photographs of the femur, kindly provided to me by Aude Bergeret.

The primate femur found at the TM 266 locality, originally numbered TM 266-01-63. Photo credit: Aude Bergeret

By Bergeret's account (and corroborated by other sources), the femur lay unrecognized in the Toros-Menalla faunal collection for almost three years after the discovery. Again, from the La Recherche article (my translation):

[I]s the bone in the photo really the femur of a hominid? And why wasn't it published along with the skull? According to Aude Bergeret, today director of the Musée de la Haute-Auvergne, in Saint-Flour, who in 2004 carried out research in Michel Brunet's Poitiers laboratory, it is because it had not been identified by the beginning of 2004. At that time, when she was studying the fossilization of animal bones found at the Toumaï site, she solicited the opinion of one of her professors on this subject, who addressed it: "During the conversation, he saw that the bone, the species of which had not yet been determined, was not the femur of an ordinary animal, but that of a hominid. Then he alerted a researcher in the laboratory. This bone, which I had many times in my hands, is indeed that figured in the photograph."

Students of anatomy will see that this femur shaft is not a super-obvious case. It lacks the distal end, the head and most of the neck. Still, its diaphysial anatomy looks like a hominoid. I'm sure that Bergeret and the professor mentioned were able to make the ID with high confidence, given the opportunity to examine it along with a comparative collection.

But as to the question of whether the femur represents a biped; that's more difficult. Most of the readily diagnostic features are missing. The remaining parts are hard to evaluate -- for example, does it have an intertrochanteric groove? That's very important to the diagnosis, and it can't really be evaluated from a photo. There might be some evidence in the cortical bone distribution at the neck, but the break is distal to the point where you'd really want to look. I don't think you could get a valid comparison of superior and inferior cortical thicknesses based on what remains. In any event, I wouldn't hazard a public guess about whether it's a biped without examining the specimen.

I will say this: Based only on the preserved anatomy, it will be more difficult to make a case that this femur is a biped than it was for Orrorin. That's not to say it's a biped or not; just to say that whoever publishes on it will have a debate on their hands.

The association

Is the femur associated with the skull? Beauvilain's picture shows them within a meter of each other.

Bone assortment at TM 266 locality. Photo credit: Alain Beauvilain

If the account in Beauvilain and Watté (2009) is correct, then their association could hardly be closer. The article in La Recherche cites the fossils' discoverer:

The discoverer of Toumaï, Ahounta Djimdoumalbaye, contests this version: "This photograph cannot have been made until after 11 o'clock, when Alain Beauvilain, who worked with another party at the site, rejoined us, my colleague Fanoné Gongdibé (deceased in 2007) and me. It shows the bones that we had found in the morning and assembled on the sand. The skull was not discovered like this, but blocked in concretions."

That quote doesn't really contradict the other account of the photograph, as Beauvilain and Watté (2009) describe the skull as having clearly been moved. The extent that the other bones may have been moved is not so clear. Beauvilain and Watté seem to have anticipated this explanation (that the bones were placed in the pictured positions by the discoverers, not found that way), as they took pains to note the lack of footprints or other marks around the bones (only on one side) and the effects of windblown sand immediately shadowing them. They argue that the bones had been in that position for a long time.

Even if Beauvilain's photo shows the bones as they were discovered, that doesn't necessarily mean that the femur and skull were deposited at the same time or exact location. The accumulation of different fossils into a small area might have happened as wind erosion scooped material away from them, changing the local topography (aeolian deflation). Close association at the site may therefore not mean much about original deposition. Plus, there remains Beauvilain and Watté's hypothesis that somebody transported and reburied the remains in the past. (I should also mention that least one reader has written to me, on the basis of knowledge of the local nomads, to express doubt about this hypothesis.)

So, it's completely unclear whether the femur and skull may represent a single individual. On the broader question of whether they represent a single species of ancient primate, we can at least observe that the femur is around the right size for the skull. It seems unlikely that two similar-sized hominoid species both lived in the same area during the limited time span represented by the stratigraphy. But I guess we have to wait and see what else may turn up in the faunal collection....

What's going on now?

None of my sources know what has happened to the bone since 2004, or what kinds of analyses may have been conducted on it. I've expected some publication on the femur for several years now (a reference to it can be found in my predictions for 2006).

Multiple sources corroborate the story that the femur was not recognized at the time of discovery or afterward. After its identification, its relevance to testing locomotor and phylogenetic hypotheses about Sahelanthropus would have been obvious to anyone. Unfortunately, we'll just have to wait.

La Recherche asked the leader of the Sahelanthropus discovery project, Michel Brunet. Here is his response (original followed by my translation):

Au Tchad, nous avons mis au jour des milliers d'ossements, qui sont en cours d'étude. Peut-être s'y trouve-t-il des os d'hominidés, mais je ne comment que ce qui a été publié dans une revue scientifique.

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.

I think this is perfectly legitimate response -- don't comment on scientific subjects until you're ready for the sun to shine on them.

Still, we have a pretty good idea of how many of those thousands of bones were found close to the Toumaï skull:

Bone assortment at TM 266 locality. Photo credit: Alain Beauvilain

Some ideas need more sunshine than others.

Now if you really want to beat the science press, it helps to have readers who take really obscure journals.

I haven't written much here about Sahelanthropus. In 2002, I joined a number of other people who doubted the evidence for bipedalism in what was then (and has since been) touted as the "earliest known hominin." Maybe it is, maybe it isn't. But we weren't convinced by the evidence. Dental similarities with early hominids were also shared with a number of Miocene ape genera, while the evidence for vertical posture, based on the position of the foramen magnum, seemed weak. We made our case in a 2004 paper in PaleoAnthropology, which is open access. Since no new evidence has come to light (or at least, to print), that's where matters stand as far as I'm concerned. I still think the evidence for bipedality in Sahelanthropus is equivocal, and that the specimen's date may be too old to be a member of the hominin lineage.

Meanwhile, also in 2004 began a strange series of events involving Alain Beauvilain, a geographer working with the original Sahelanthropus excavation project. I have no personal knowledge of the details, aside from the published record -- so that's what I'll stick to.

Yes, this story does end with camelherders burying fossils....

Dental associations of Toumaï questioned.

First, Beauvilain teamed up with a dentist named Yves Le Guellec, publishing a short paper in the South African Journal of Science that questioned the assignment of a tooth to the Toumaï mandible. Their suggestion was that the tooth must represent a second individual, and that the original research team had mistakenly glued it into the mandible. They did not question other aspects of the original research, and concluded their paper:

The present analysis, based on some Sahalanthropus paratypes, is only one element of the discussion about this genus. It does not modify the basis of the debate concerning the systematic position and palaeoecology of Sahelanthropus (Beauvilain and Le Guellec 2004:144).

That seemed pretty milquetoast to me, and if I'd been blogging at the time (which I wasn't), I might not even have taken notice.

What was newsworthy about Beauvilain's comment was the reply by Brunet's Sahelanthropus research team. They provided images, including CT scans, that supported their original assignment of the tooth to the mandible. And then, the reply was followed by a statement signed by 28 other paleoanthropologists, led by F. Clark Howell. Here is that statement in its entirety:

Sir, — We, the undersigned, have carefully examined the photographs and digital crown images of a fossilized third molar from the upper Miocene of Chad. This tooth was originally identified by the discoverers (Brunet et al. 2002, Nature 418, 145–151) as a right third mandibular molar. A recent paper by Beauvilain and Le Guellec (2004, S. Afr. J. Sci. 100, 142–144) claimed that this tooth had been misidentified and was in fact a left lower third molar. Based on crown anatomy evident in the images examined by us, we confirm the identity of this tooth as a right molar, as originally published by Brunet et al. (2002).

Rex Dalton covered the reply in Nature, in a piece titled, "Brickbats for fossil hunter who claims skull has false tooth". All I can add is, I hope this crew never comes after me.

This exchange continued for a couple more letters, as Beauvilain and Le Guellec found errors in the analyses published by Brunet and colleagues. They may not have been correct about the tooth, but they had showed a string of apparent mistakes made during the research on Toumaï.

Stratigraphy of Sahelanthropus questioned.

That was all in 2004. In 2008, Beauvilain published an article in the South African Journal of Science in which he asserted that neither Toumaï (the type specimen of Sahelanthropus tchadensis) nor the type specimen of Australopithecus bahrelghazali had been found in situ by Brunet's team. This short article was apparently a reply to a PNAS report on the dating of the two discoveries by Anne-Elizabeth Lebatard and colleagues (2008). That paper placed the two fossils within stratigraphic sequences and provided dates for the strata. Beauvilain (2008) wrote that the placement could not be certain:

From January 1994 to July 2002, the author of the present note was in charge of every palaeontological field expedition that took place in the Chadian desert. In the interests of scientific accuracy, he is compelled to state formally that neither of these fossils was found in situ. The most appropriate word to employ for the two fossils would be that they were 'collected' from their respective localities, which are the sites TM 266 in Toros Menalla and KT 12 in Koro Toro for S. tchadensis and A. bahrelghazali, respectively.

...

The photograph taken by the author at the moment of discovery has been widely published but never with a proper explanation. He thought that the image was sufficiently evocative to indicate the lack of stratigraphical context of the fossil. It is time to correct this omission. In the image, the hollow in the sand to the right of the skull is the exact spot at which Toumaï was found. Almost all the fossils from TM 266 were in similar situations with respect to the substrate. By a curious choice, the photographs of Toumaï published by [Brunet's team] as representing its field context are in reality those of a darkened resin cast, posed in the desert on a ridge of sand created by the northeast winds in February 2004.

Beauvilain did not in this article suggest that the true ages of the fossils might be radically different than those of the strata reported by Lebatard et al. (2008) -- a substantial depth of deposit around the Sahelanthropus site falls within a time range between 6.8 and 7.12 million years ago. He does suggest that the aeolian pattern of erosion in the area and some faulting may have caused undercutting of some fossils and substantial movement against the vertical section.

Cosmos magazine picked up this story last year, although I have not seen it reported elsewhere. I noted it here at the time. I haven't seen any reply to Beauvilain by the rest of the excavation team.

That's the published record. What did Beauvilain accomplish with this paper? He reiterated his position on the field project and gave clear reasons why he had stepped forward to publish his note on the specimens' provenience. This additionally presented the context in which he took his own photos of the Toumaï discovery. The photos are the crucial element.

Buried facing Mecca?

Now the story gets weird. Beauvilain's new paper with Jean-Pierre Watté has been blowing into paleoanthropologists' inboxes around the world. My library doesn't get the Bulletin de la Société Géologique de Normandie et des Amis du Muséum du Havre, but I've gotten copies of it from three different sources. Considering how widespread my sources are, I know that a good fraction of my colleagues have at least had their chance to read it.

I don't tend to pass around mere rumors, even if they're really juicy (you know who you are....). But this is no rumor -- it's a real publication. Nobody quite seems to know what to think about it. So let's get it out in the open.

Here's the English version of the abstract:

Was Toumaï (Sahelanthropus tchadensis) buried?

Photographs taken when the skull of Toumaï was discovered establish that the holotype of one of the earliest known hominid species was probably reburied in the recent past. Taphonomic analysis reveals the likelihood of one, perhaps two, burial(s) which seemingly occurred after the introduction of Islam in the region. Two other hominid fossils (a left femur and a mandible) were in the same "grave" along with various mammal remains.

I'm going to give a fairly long summary of their argument, providing English translations of the key points. They have no direct evidence that the bones were altered in position or deliberately arranged, but they do present an interesting circumstantial argument. There are essentially four points:

1. The skull was associated with an unusual concentration of fossils. As Beauvilain and Watté (p. 20, my translation) introduce their paper:

While fossils of this site are distant from each other, scattered at random and without concentration of large size, Toumai was part of a pile of bones. In general, with the exception of skeletal remains belonging to a single individual, concentrations of fossils are rare in Djourab sites. That is why the Chadian coauthors to the discovery said this cluster was a "dustbin of palaeontologists." This expression does not correspond to reality. The "garbage" of paleontologists, and geologists, experienced in this area of Toros-Menalla, as well as that of KB, are of a different nature: broken bones, brittle, "digested" by the desert crust, not identifiable, with sometimes broken glass of beer or demijohns. A skull could not have been left there, unless it was completely hidden beneath the crust. An examination of Figures 1a and 1b can offer a different explanation.

The picture below shows the association. It is not possible to say how unusual this may be without some statistical study of the area around the site. I'm noncommittal, but am willing to accept Beauvilain and Watté's description at face value.

2. The arrangement of the bones. I can't discuss the paper without showing the photographic evidence that Beauvilain and Watté rely upon. So here's Figure 1b from the paper:

According to the paper, this is the layout of the Toumaï skull and surrounding fossil bones at the time of discovery. Beauvilain and Watté suggest that this is an artificial assemblage of fossil bones. As you can see, they have labeled "two parallel lines" along which the bones are arranged. They do not judge this to be a likely result of aeolian erosion in situ, and consider it a possible sign of a deliberate arrangement of the fossils.

As I've noted, Beauvilain (2008) established the reason why he has photos of the original find. With photographic evidence such as this, the constant worry is that some kind of alteration has been made with Photoshop. Has false color been added? Have objects been composited together? I'm no forensic photo expert, but I see no obvious signs of trickery.

Are they really two parallel lines? Clearly there is at least one straight line here (the top one in the figure), with other fossils arranged in rough accordance with that line. It's not random, but whether collection in an aeolian depression might explain the linear arrangement, I don't know.

3. When it was found, the skull was lying on its left side, with its right side exposed. But both sides of the skull and its adhering matrix appear to have been equally eroded and patinated, including a process of "bluing" the dark matrix, a chemical alteration that occurs on surfaces exposed to air and light. This suggests that the entire skull was exposed for some time. This is not explicable if it was eroding out of a rock layer in situ, but only if it had been rotated, either by aeolian forces undercutting it for some time or because the skull was transported from some other location (p. 23-24).

Also, in favor of the skull having been moved, Beauvilain and Watté suggest that the matrix adhering to the skull appears to be somewhat different from the other fossils:

Par ailleurs, aucune trace n'est visible sur le crâne ou sa gangue de ce ciment blanc, très siliceux et très adhérent aux fossiles, qui caractérise les autres pièces collectées à TM 266, comme celle de la mandibule de Sahelanthropus TM 266-02-154-1, et sur un grand nombre d'ossements de la zone dite de Toros-Menalla. Ces différentes pièces n'ont donc pas strictement le même age (23).

In addition, no trace is visible on the skull or its matrix of this white cement, very silicious and adhering to fossils, which characterizes the other pieces collected at TM 266, including the mandible of Sahelanthropus TM 266-02-154-1, and on a very large number of bones from the zone called Toros-Menalla. These different pieces are therefore not strictly the same age (my translation).

I think these points are fairly compelling. That skull ought to be asymmetrically weathered and patinated unless it has been rotating around a lot. It ought to be more weathered than the surrounding bones, which clearly present a lower profile to the elements.

4. The line formed by the fossil bones is oriented toward Mecca. I'll say right off, this is the least convincing element of their argument. The "parallel lines" in the figure are northeast-southwest, which is only "toward Mecca" in the general sense (as described below). Given a line, it has to point in some direction, and there's a good chance that it will be within 45 degrees of any random line.

However, it does help to tie the story together. Here is the full scenario, as outlined in the paper's conclusion (my translation of pp. 24-25):

The location of the skull in relation to the two rows of long bones evokes the disposal of a body reduced to the status of a skeleton.... This arrangement cannot be natural. In view of its configuration, it is suggested that it arose from the desire to give these remains the honor of a burial. The skeleton was reconstructed from the skull conceived as "human". Indeed, this head, which looks like the head of a man, cannot remain indifferent. In this perspective, the authors of the burial -- if that is indeed the case -- would have done their best, according to their anatomical knowledge and the fossils of animals they could find here and there, and that they may have confused with human bones, in order to bring the skull together with the other elements of his body. They put a close to the humeral head and distal end, well-oriented, a femur at the other end of the "corpse". Toumai therefore is subject to a burial in recent times.

Why a burial? The abundance of fossils in this part of the desert makes it so that today, people remark on it but do not think more than that some stones resemble animal bones, including jaws, without giving them much importance. Children play with them. But to the contrary, this skull that so resembles a human skull could not be taken for a toy and abandoned to children.

Who could have been the authors of this burial? The orientation given to the "body" correponds to the diagonal northeast-southwest. This direction is important: it is the line toward Mecca. This burial, if such is the case, could have been done by nomads who cross the region regularly. Muslims since the 11th century with the conversion to Islam of the sovereigns of the first kingdom of Kanem -- the capital of which lay not far from the place where Toumaï was found -- these populations became religious enough to offer a decent burial to their human brothers. In fact, the Muslim religion makes it an obligation to inter cadavers. The precise tradition in which the body must be lain out with the head oriented in the direction of Mecca. Without instruments, believers take the direction of the rising sun, which, near the Tropic of Cancer, is highly variable during the year when it may be in either the northeast or the southeast.

Is it a convincing scenario? It seems a little far-fetched if you imagine that the desert was an untouched wilderness where humans would never have laid eyes on these objects. But to give them as much credit as possible, Beauvilain and Watté note that today's "desert" was before 1900 much more frequently trafficked than today. Human activities are still widespread in the area and were formerly more so. This is not untrammeled wilderness, and according to the paper it might be very likely for a humanlike skull, laying on the desert floor for decades, to have been encountered by local people and reburied.

At this point, it is an ethnographic question: Other burials must periodically emerge from the ground. What happens to them? Is there other archaeological evidence of reburial of skeletal remains, either in this immediate area or elsewhere in North Africa? I haven't found any other citations of such a practice, but it must be rare and episodic in any event.

What does this mean?

At the end I have to say I'm ambivalent. I have no real reason to accept or deny this new report or the original studies. Beauvilain has a record of pointing out genuine inaccuracies in the publications of Brunet's group. Beauvilain and Watté base their specific claim of a recent reburial is only on circumstantial evidence, which is tenuous.

Yet the evidence does seem sufficient to support Beauvilain's 2008 position as regards the surface collection of the specimens and the possible transport of the skull. Beauvilain (2008) claimed that Toumaï had not been discovered in situ, and that is relation to the published stratigraphy was therefore unclear. At one level, this current paper says nothing more.

Sahelanthropus may still be precisely what its discoverers have claimed: A Late Miocene representative of the human lineage. The fossil is what it is, and the nearby sediments are Late Miocene in age. If people had transported it some short distance and reburied it, it would still probably be Late Miocene in age -- although I would want to see somebody do a systematic comparison with local sites to be sure.

At worst, the skull represents a somewhat different date, and is not clearly associated with the accompanying fauna. In that case, a fuller understanding of the local paleontology, along with (hopefully) new discoveries of Sahelanthropus, should clarify matters.

Beauvilain himself appears to be a big booster for Sahelanthropus (having published a trade book on the discovery) and has maintained in each of his critical publications that it is likely the first member of the human lineage. He seems to be aiming at precision in the descriptions, not trashing the species and not offering any new interpretation of its anatomy.

But I'm not a big booster of Sahelanthropus. And there's one significant thing in this paper that even the sharp-eyed might miss. Something that you might reasonably wonder about, considering the discoverers and describers of Sahelanthropus have never once mentioned it in print.

Toumaï's skull was found alongside a femur.

More on this later....

References:

Beauvilain A. 2008. The contexts of discovery of Australopithecus bahrelghazali (Abel) and of Sahelanthropus tchadensis (Toumaï): unearthed, embedded in sandstone, or surface collected? S Afr J Sci 104:165-168.

Beauvilain A, Le Guellec Y. 2004. Further details concerning fossils attributed to Sahelanthropus tchadensis (Toumaï). S Afr J Sci 100:142-144.

Beauvilain A, Le Guellec Y. 2004. Reply to Brunet et al. S Afr J Sci 100:445-446.

Beauvilain A, Watté J-P. 2009. Toumaï (Sahelanthropus tchadensis) a-t-il été inhumé? Bulletin de la Société Géologique de Normandie et des Amis du Muséum du Havre 96:19-26.

Brunet M, Guy F, Pilbeam D, Lieberman DE, Likius A, Mackaye HT, Ponce De León MS, C.P.E. Zollikofer CPE, Vignaud P. 2005. New material of the earliest hominid from the Upper Miocene of Chad. Nature 434:752‑755. doi:10.1038/nature03392

Brunet M and 28 others. 2004. Sahelanthropus tchadensis: the facts. S Afr J Sci 100:443-445.

Dalton R. 2004. Brickbats for fossil hunter who claims skull has false tooth. Nature 430:956. doi:10.1038/430956a

Howell FC and 27 others. 2004. Untitled. S Afr J Sci 100:446.

Lebatard A-E and 13 others. 2008. Cosmogenic nuclide dating of Sahelanthropus tchadensis and Australopithecus bahrelghazali: Mio-Pliocene hominids from Chad. Proc Nat Acad Sci USA 105:3226-3231. doi:10.1073/pnas.0708015105

Wolpoff MH, 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. PDF

I just read the new paper by Philipp Gunz and colleagues, titled, "Early modern human diversity suggests subdivided population structure and a complex out-of-Africa scenario". That's a mouthful.

The late Middle Pleistocene population of Africa was genetically variable, and that genetic variability is probably the biggest component of genetic variation still remaining in living humans. Moreover, the phenotypic variability of the Levantine sample has been recognized since its initial description by McCown and Keith (1939). So to read this is not surprising:

Seemingly ancient contributions to the modern human gene pool (36) have been explained by admixture with archaic forms of Homo, e.g., Neanderthals. Although we cannot rule out such admixture (37), the clear morphological distinction between AMH and archaic forms of Homo in the light of the proposed ancestral population structure of early AMH to us suggests another underestimated possibility: the genetic exchange between subdivided populations of early AMH as a potential source for ‘‘ancient’’ contributions to the modern human gene pool (9, 36).

I've stressed the importance of African population structure before (e.g., Hawks et al. 2008). So I agree completely with this part of the interpretation in the paper: African variation was larger than in other regions, and it was important.

But that being said, these morphometric comparisons are not very straightforward. Some comments:

1. Phenotypic variance is not a measure of genetic variance. If we see a population that has a large measure of phenotypic variability, it does not mean that the population had much genetic variability. Perversely, genetic variability can sometimes be lower in a population that has greater phenotypic variance -- often because genetic drift can cause a loss of epistases that once constrained the phenotype. In some cases environmental variance may actually increase when the additive genetic variance declines, because of a loss of developmental robusticity. In any event, we can't just go from a variable phenotype and infer that there's variation in genotypes.

2. There's no evidence for subdivision here. They measure a high phenotypic variance within the sample they refer to early modern humans. But that variance is expressed not mainly between geographic locations in the sample, but within them. Qafzeh 6 and 9 are far apart; Jebel Irhoud 2 and Skhul 5 are close together. The East African fossils Omo 2 and LH 18 are far apart. This isn't subdivision, it's just high within-population variance.

3. Weird sample composition. The early modern human sample includes the African and Levantine crania complete enough for analysis. But why lump these? Why is the South African Fish Hoek skull lumped with Upper Paleolithic Europeans?

4. Temporal range. There are two samples here that have a high average distance between nearest neighbors in the sample: "archaic" humans and early modern ones. What these two samples have in common is that they each cover a much larger range of time than the other samples. The early modern sample spans more than 100,000 years by current dates. That's more 80,000 years longer than the Upper Paleolithic sample, 50,000 years longer than the Neandertal sample -- a huge component of variance that is uncontrolled in the other samples.

5. Principal components. PC axes are those that account for the largest covariances in the sample. If two samples are lumped together, there is a within-population component of variance and a between-population component. These may be partly independent in their effects on the total variance, or they may not be. In any event, if we derive the PC structure from the total sample, or even from the individual samples pooled together, the larger samples will weight the PC structure more toward the factors that explain their within-sample covariances. In this case, we have many more recent humans than fossil ones, and many more archaic humans and Neandertals than "early modern" humans. It's hard to have an intuitive idea about the biases that can result from sample composition, and that's a big reason for caution.

Those are all reasons for re-examining the results in different ways. In particular, if I were doing this kind of analysis, I would repeat it for subsets of the cranium, where I could include a larger number of fragmentary fossils. If the African-Levantine sample is really unusually variable, that should hold up strongly when we examine parts as well as the whole cranium.

Well, although I listed several reasons for caution, we can ask how to interpret the study's conclusion:

Any model consistent with our data requires a more dynamic scenario and a more complex population structure than the one implied by the classic Out-of-Africa model.

If we take the high variance of their "early modern" sample at face value, what we have to conclude is that later humans evolved substantially less phenotypic variance than African-West Asian people who lived between 200,000 and 90,000 years ago. Genetics tells us that there was no massive genetic drift during the time span after 90,000 years ago within Africa. Thus we must conclude that some other force resulted in a significant restriction of the phenotypic variation of recent humans, including people who lived as long as 40,000 years ago.

My hypothesis would be natural selection on some significant subset of phenotypic characters, which reduced the phenotypic variance of most of the cranium by pleiotropy. An out-of-Africa migration is not sufficient to explain the reduction in variance, because all modern humans are limited in phenotypic variance, not only non-Africans. Selection on some significant set of genes would help to explain why the ancestral African population predominated within the last 100,000 years. This selection would have predated most of the recent acceleration we observe in the genomic variation of current populations -- indeed, whatever set of genes was strongly selected before 50,000 years ago might have been fixed long ago.

A wave of selection can promote dispersal and demographic growth without the necessity of complete population replacement (cf. Eswaran 2002). A substantial transition in the genetic background would alter the phenotypic effects of any genes that remained in non-Africans from their local ancestors. In other words, the answer about what happened to fossil humans outside of Africa depends on the kind of events that happened inside Africa. So from that perspective, this research is very interesting.

References:

Gunz P, Bookstein FL, Mitteroecker P, Stadlmayr A, Seidler H, Weber GW. 2009. Early modern human diversity suggests subdivided population structure and a complex out-of-Africa scenario. Proc Nat Acad Sci USA (early online) doi:10.1073/pnas.0909160106

Eswaran V. 2002. A diffusion wave out of Africa: the mechanism of the modern human revolution? Curr Anthropol 43:749-774.

McCown TD, Keith A. 1939. The Stone Age Man of Mount Carmel: The fossil human remains from the Levalloiso-Mousterian. Clarendon Press, Oxford.