What have I been doing?
I spent much of the weekend digesting and writing notes on a couple of papers from last week, including the widely-reported Genographic Project paper on the mtDNA of Khoisan and other Africans.
After putting around 5000 words into it, I have decided this is becoming more of a research project than a blog post. It is now possible to build a much more interesting picture of the evolution of Africans continent-wide during the late Middle Stone Age.
This picture does not include many of the elements suggested in the press reports accompanying the paper. In particular, there is no evidence for the proposition that tens of thousands of years of droughts decimated humans down to a small number of tiny bands, which later reunited to conquer the earth. That account goes far outside the science presented in the AJHG paper by Behar and colleagues.
We are working in a wonderful time, when data from many different genetic projects are becoming available to examine the detailed pattern of evolution in parts of the world where archaeology and physical anthropology have been incomplete. But there has been a tendency by many geneticists to exaggerate the weaknesses of traditional artifactual and skeletal evidence. This is manifested in an unwillingness to approach multiple data sources with the idea that they must each be consistent with a single population history.
Since we have not only new genetic evidence, but also new fossil and archaeological evidence coming online, the time may have come for a new synthesis of the prehistory of Africa.
Omo Kibish redating
The news stories (nature.com) are focusing on the idea that the "earliest" modern humans are now 35,000 years earlier than they had been. This is the amount by which the Omo Kibish specimens are now believed (McDougall et al. 2005) to be older than the previous contenders for "earliest modern humans," the 160,000 year-old Herto hominids (White et al. 2003). A bit of a discussion has been underway on the Palanth forum as to whether the 195,000 year estimate is really warranted, or whether there is more properly considered a broader range of error.
It is important to have good stratigraphic placement and dates for the Omo Kibish specimens. Most of the Middle Pleistocene African fossils are associated only with poor dates or imperfectly known proveniences. Aside from the recent Herto sample, the dates for other important specimens are truly uncertain. So the knowledge that these hominids are broadly contemporaneous with Herto is immensely valuable.
Why are the Omo Kibish hominids considered to be modern?
This depends on one's definition of "modern humans." Many paleoanthropologists do not accept a distinction that sharply separates "modern" humans from "archaic" humans. For these scientists, the Omo Kibish specimens may simply be considered as representatives of their time and place, part of an evolutionary series leading to recent humans.
There is no question that features of recent aspect occur within the late Middle Pleistocene African sample. Especially Omo 1 has similarities in overall cranial shape with more recent people. Such similarities also may characterize its facial form, although these details are subject to the reconstruction. Taking the Omo skulls as a sample, together with the Herto sample, the full range of anatomy spans from relatively modern to substantially archaic. Here are some pocket descriptions (leaving out the child's skull BOU-VP-16/5):
- Omo 1: The occiput is rounded in profile, with only slight flattening of the parietals above lambda. In posterior view, the outline of the skull shows a maximum breadth relatively high on the parietal bones, narrowing significantly lower on the temporals toward the cranial base. The supraorbital torus is not greatly thickened even at the midline, and it thins toward the edges in a form that is continuous with the frontal squama. The interorbital space is relatively narrow. And as reconstructed, the skull appears to have both malar notches and a chin.
- Omo 2: Here, the skull is markedly more angled in the occiput than in Omo 1. The maximum breadth of the skull is at the base, across the temporals, and the sides of the skull are more or less vertical. There is a well-marked angulation of the parietal bones, meeting in a rounded keel. There is a slight angular torus on the parietal, and a well-marked nuchal torus transversely extensive across the occiput. But the frontal bone is continuous into the supraorbital region with no sulcus separating them, and the supraorbital torus itself is relatively thin laterally--perhaps as much or more so than Omo 1.
- BOU-VP-16/1 (Herto): The skull has a distinct angulation in the occiput, as great as Omo 2, with a very long nuchal plane. The skull appears to be slightly broader across the parietals than at the base, but the sides are essentially vertical: there is no distinct parietal boss. The nuchal torus is marked across the occiput, with a distinct downward-projecting inion. The browridge is moderately thick centrally, with a strong superciliary portion, and a clear sulcus dividing it from the curving frontal profile. There is a clear division between this superciliary arch and the lateral torus, which at its lateralmost extent is in the same range of thickness as the Omo 2 lateral torus. The zygomatic bone is very large, with a massive forward-facing cheek, hollowed into a canine fossa medially and malar notch inferiorly.
Several commentators have raised the issue of whether this sample contains multiple species (one going so far as to posit that the "species" immediately ancestral to our own might be preserved alongside the "modern humans" in the personage of Omo 2). A lateral comparison of the three skulls (where their comparable parts are most visible) shows that the differences are not that extensive. The Herto skull and Omo 2 are very similar in profile, with BOU-VP-16/1 being slightly higher in the forehead. Omo 1 contrasts with these in its rounded occiput, but the frontal profile of all three specimens are similar, as are their lateral torus thicknesses. Omo 1 and 2 diverge greatly in the position of their greatest cranial breadth and shape of their cranial walls; BOU-VP-16/1 is intermediate between them. All three are robust, with Omo 1 the least robust of the three. Presumably, all three are males. Their variation is extensive, but not surprising for three crania in a single region of the world.
Are they modern humans? As White and colleagues (2003) show, the Herto skull is outside the range of all recent humans in several cranial measurements. This is no doubt true for Omo 2 as well (although possibly not for Omo 1). But these are not recent, they are ancient. As a sample, they are certainly significantly different from any living sample. They are also certainly significantly different from Neandertals, and from earlier Africans.
So do we define "modern" humans in contrast with some earlier group? Or do we define them based on the variability within living people?
The answer here really is in the word "definition." If modern humans were really an evolutionary individual--a "thing" that could be discovered--then we shouldn't have to define them. We should be able to discover the boundaries of the group by examining discontinuities among fossil specimens. The fact that we have to find a definition (and that we have such trouble doing so) is in my mind sufficient to suggest that "modern" humans are not an evolutionary individual.
References:
McDougall I, Brown FH, Fleagle JG. 2005. Stratigraphic placement and age of modern humans from Kibish, Ethiopia. Nature 433:733Ð736. Nature
White TD, Asfaw B, DeGusta D, Gilbert H, Richards GD, Suwa G, Howell FC. 2003. Pleistocene Homo sapiens from Middle Awash, Ethiopia. Nature 425:742Ð747.
The hygienic dater
I've just been reading a useful paper by Andrew Millard, which reviews the chronometric dates of African and Near Eastern fossil hominids from the Middle and early Late Pleistocene. The overall theme is that we don't know the dates nearly as well as we would like -- or as well as many comparative analyses have assumed.
The highlight is the list of specimens with primary references to different date estimates. Anyone with a good training in paleoanthropology probably has a feel for which specimens have relatively good dates and which are real hands-up-in-the-air cases. Kabwe makes for a good example of the latter:
Kabwe (Broken Hill), Zambia. The remains of "Rhodesian Man," along with faunal remains, were discovered in 1921 by miners (Klein, 1973). The principal dating is based on Klein's (1973) assessment that the fauna is similar to that at Elandsfontein and broadly similar to those from Olduvai Gorge Upper Bed II through to Bed IV. There are no chronometric determinations. On the basis of the faunal correlation to Olduvai (Fig. 1), an age of younger than 1780 ka and, depending on the chronology for Olduvai, either older than 990 ka (on the long chronology) or, more likely, older than 490 ka (on the short chronology) may be assigned (see under Olduvai above). This is consistent with Elandsfontein being older than 330 ± 6 ka (Table 1).
Millard's discussion of "chronometric hygiene" takes up much of his discussion. This is nothing more than the simple idea that we should weed bad dates out of our analyses. For example, he singles out Florisbad as a specimen that has been handled poorly in the literature:
Use of the literature. In conducting this review of the chronometric evidence for African and Near Eastern hominids, the search for the detailed chronometric data was hampered by overreliance of many authors on the secondary literature. It is not uncommon to find a date cited from a publication, which upon checking simply cites another publication, which cites another, which cites the paper that first suggested the date. Frequently in such a chain of citations, the justification for the original date is lost, and in some cases, error limits disappear. For example, the ESR date of 259 ± 35 ka for the Florisbad hominid (Grün et al., 1996) can be applied to the Florisbad fauna, but somehow in the discussion of Stynder et al. (2001), this becomes simply "a maximum age of around 250 ka" (p. 372) for the Florisbad Faunal Span, and in McBrearty and Brooks (2000), it becomes a bald 260 ka age without any uncertainty for the Florisbad hominid itself. Sometimes, the primary proposal for a date is based solely on comparisons of morphology to the best-dated fossils at the time of publication, and for later papers to suggest evolutionary sequences based on this date is obviously problematic. Given the flux in dating methods, the fact that problems have often been identified some time after the introduction of these methods, and the changing understanding of the dates of faunal successions, every author should be beholden to check the basis of the dates cited and apply some basic chronometric hygiene (Millard 2008:19).
Of course, there is an irony here, since Millard's effort has generated a massive secondary source listing date estimates for all these hominids! I agree whole-heartedly with his sentiment, though -- everyone should do a better job of reading and citing papers.
But the effect of all this hygiene is to emphasize that most of the Middle Pleistocene remains a muddle, with very few well-resolved dates across the entire span. Millard describes faunal correlations as a relatively weak source of evidence in Africa. Above the time span effectively covered by ESR/TL, there is little to rely on.
References:
Millard AR. 2008. A critique of the chronometric evidence for hominid fossils: 1. Africa and the Near East 500-50 ka. J Hum Evol (in press) doi:10.1016/j.jhevol.2007.11.002
The "dark matter" of modern human origins
I'm just looking through the January/February 2008 Evolutionary Anthropology, which is all about modern human origins in Africa. The special issue resulted from a conference at Stony Brook, along with a few additions to round out the topic.
I'll have some things to say about these articles, but one thing struck me. I'll describe the problem:
Dan Lieberman's paper, "Speculations about the selective basis for modern human cranial form," discusses five categories of functional requirements that might have been involved in the evolution of the "modern" human cranial anatomy. Each of these imposes distinctive requirements on the form of the head -- not all of which are fully understood -- but all of which changed in ways that parallel the basic changes in cranial form of the Late Pleistocene.
But Tim Weaver and Charles Roseman's paper, "New developments in the genetic evidence for modern human origins," claims that the modern human cranial anatomy originated by genetic drift, without any substantial selection:
Evolutionary quantitative genetic analyses, in fact, show that Neandertal and modern human cranial differences can be explained by genetic drift, making it unlikely, at least for the cranium, that modern human anatomical features were spread by natural selection rather than a range expansion out of Africa. An important point is that these analyses do not simply compare the magnitude of the morphological differences between Neandertals and modern humans; they are multivariate tests of how the patterns of covariation across different cranial measurements compare to those expected for divergence by genetic drift. Natural selective hypotheses designed to account for Neandertal and modern human cranial differences would also need to show multivariate consistency with the observed patterns of variation. While it may be possible to imagine natural selective scenarios that mimic genetic drift for a single measurement, such as fluctuating directional natural selection, the scenarios become much less plausible for multivariate patterns of variation (Weaver and Roseman 2008:78).
Both these papers cannot be correct. A full text search of Lieberman's paper does not find the words "drift" or "random," and "neutral" only appears as part of "neutral horizontal axis." Yet Weaver and Roseman cite the neutrality of cranial form as the main evidence against Eswaran's model of an adaptive dispersal of cranial form. According to them, all of Lieberman's "speculations" must be wrong.
I thought maybe I could get some insight into this dilemma by reading Günter Bräuer's paper, "The origin of modern anatomy: by speciation or intraspecific evolution." That title sounds fairly clear -- if we're talking about a speciation of modern humans to explain their anatomy, that sounds like the kind of rapid change that ought to indicate selection of some kind.
Bräuer shows some skepticism toward Lieberman's ideas about cranial evolution:
In my view, Lieberman, McBratney, and Krovitz's interpretation that anatomical modernization can be boiled down to just a few autapomorphies or genetic changes will be difficult to accommodate within the current fossil evidence (Bräuer 2008:27-28).
OK, but does this disagreement mean that Bräuer is likewise skeptical of adaptive hypotheses to explain modern cranial form? Again, a full text search fails to find the words, "drift," "neutral," or "random." But neither does it find the word "selection." Bräuer is concerned with describing the pattern of evolution of the modern human cranial form, but is entirely noncommittal on the question of why it evolved. That would seem to be problematic in itself: wouldn't we expect a different pattern of evolution if natural selection caused the changes, than if genetic drift caused them? Wouldn't the two causes make different predictions about the role of speciation in the process?
I'll have more to write about Bräuer's interesting paper, but on this issue, I think that is all I can extract from it. Osbjorn Pearson's paper, "Statistical and biological definitions of 'anatomically modern' humans," has more to say on the issue. Pearson cites the work that suggests modern human cranial form evolved under random genetic drift, saying:
Ideally, one would like to partition morphological distance into differences due to genetic drift, adaptation, and environmental interactions with ontogeny. Recently, several promising studies have shed light on these issues, including the amount of morphological diversity in recent humans that likely reflects genetic drift and the effects of the toughness of foods on the cranial morphology and occlusion of nonhuman primates, retrognathic mammals (for example, hyraxes), and humans from different parts of the world. Nevertheless, much remains to be done before these relationships become completely clear (Pearson 2008:40-41).
He later suggests (p. 44) that "rapid morphological change due to drift during population bottlenecks" may be involved in the evolution of modern cranial form. On the other hand, Pearson also suggests that "selection for new, advantageous traits or genes, or some combination of the two [selection and drift]" may have occurred. That would seem fairly noncommittal.
However, Pearson's description of the series of events -- a stepwise, sequential series of anatomical changes ultimately in a worldwide context up to and including the Holocene -- seems pretty unlikely to result from genetic drift alone. Indeed, Pearson writes,
In common with many other parts of the world, [African] crania that have dimensions or suites of morphological traits that make them statistically indistinguishable from the living populations appear only during the Holocene (Pearson 2008:45).
If the evolution of modern cranial form is a process that continued into the Holocene, it is quite impossible to have been caused by drift alone, since the effective population sizes of human populations were too large, and drift could hardly have caused a "nearly universal pattern of gracilization" (ibid.). So Pearson's paper certainly heightens the contrast between the adaptive and drift scenarios. If the events are as Pearson describes them, the "genetic drift alone" hypothesis must be false.
Philip Rightmire's paper is about earlier events, and Chris Stringer and Nick Barton's paper is a conference review. That leaves only Ian Tattersall and Jeff Schwartz's paper, "The morphological distinctiveness of Homo sapiens and its recognition in the fossil record: clarifying the problem," to clarify the problem.
Tattersall and Schwartz direct their attention to the kinds of features that are suitable for identifying a species from the fossil record -- uniquely derived features, or "autapomorphies." In their view, species must be accurately diagnosed from sets of specimens ("alpha taxonomy") before any kind of evolutionary hypotheses can be tested.
Because of this, they don't talk very much about the kinds of evolutionary forces that might cause the patterns they see. The paper includes only one reference to "random" and "adaptive," both in a single sentence:
However, there are some materials of this period [the late Middle Pleistocene] that fall outside, but not far outside, the strictest definition of Homo sapiens as based on the living species. Most of these (for example, Border Cave 5, Boskop, Fish Hoek, Klasies River Mouth except for AP 6222, and maybe Cave of Hearths) form a generally poorly dated South African group in which cranial structure largely conforms to the modern Homo sapiens morphology except that, most notably, the bipartite brow and/or the inverted-T-shaped chin are lacking. Do such fossils represent distinctive and now extinct populations of Homo sapiens that lacked two or more of the most striking autapomorphies of the living species merely as a result of random (or even adaptive) population variation? Or did they belong in life to one or more distinctive reproductive entities whose histories did not impinge, at least biologically, on that of today's Homo sapiens? (Tattersall and Schwartz 2008:52, emphasis added)
The bolded sentence is important. Tattersall and Schwartz view adaptive and random variations as equivalent: small changes between populations that may occur even without the kind of significant isolation that would invite a taxonomic interpretation. They contrast these in the next sentence with "distinctive reproductive entities whose histories did not impinge." And they are correct; modern human populations have morphological differences as a result of both selection and drift, and their histories certainly have impinged on each other.
But it makes a difference whether selection or drift was the cause of changes, because selection is more powerful than drift. Weak selection can cause a level of morphological differentiation that would require long isolation by random drift alone. If selection were involved in African regional differentiation, there may be no reason to posit "distinctive reproductive entities whose histories did not impinge" -- in fact, their histories almost certainly would have impinged.
In other words, the relation of the pattern of features to the taxonomic status of the populations depends on the evolutionary forces that generated the pattern.
As Weaver and Roseman note, their hypothesis that modern human cranial form evolved neutrally depends on the pattern of evolution of different features, not the amount of evolution of any single feature. But the amount of evolution must still be explained; under their hypothesis, it must have occurred in small populations over a substantial period of time. In their hypothesis, the cranial differentiation of African late Middle/early Late Pleistocene fossils would have emerged during relatively long periods of parital or complete isolation. Under that hypothesis, Tattersall and Schwartz would be correct to place these fossils into different taxa, only one of which was ancestral to living people -- or at least principally ancestral, allowing for some small amount of hybridization and introgression.
In contrast, Lieberman's adaptive hypotheses are consistent with the evolution of modern human cranial morphology within a broader, larger population. Patterns of selection may explain the variation among the fossils. Today's humans may have emerged from a population with substantial cranial polymorphism. That scenario would seem to be consistent with the patterns described by Pearson -- in which modern human cranial variation does not standardize until very late, perhaps even Holocene times. Only selection could cause this kind of evolution within the large populations of the last 10,000 years, or even within the large populations of the last 70,000 years.
I picked this problem first, because it was the first to stand out to me in the papers. It does seem a fairly glaring contradiction. I don't expect the authors to have noticed the contradiction in advance; I think that they approach the question of human origins from fundamentally different viewpoints.
As you can tell, two of the papers are not concerned with the causes of evolution at all -- their aim is to map the pattern of morphological variation onto putative speciation events. But it seems to me that if we approach the fossil record with the idea that speciation is the major cause of such patterns, then we have already assumed how the evolution happened. It may not have escaped your notice that this is the major reason for disagreement about modern human origins: One group of authors wants to assume the conclusion, foreclosing further discussion.
I don't have any complaints about the papers that were chosen for the issue -- in fact, I'm interested in reading the current opinions of all these authors. So far, I would say that each paper is a well-written expression of its authors' ideas, and I appreciate having all that in one place.
But it does seem a little strange that a special issue devoted to modern human origins in Africa doesn't have more, um, diversity of opinion. Several of the papers discuss multiregional evolution. They apparently believe that it is an important enough viewpoint to include their reasons for disbelieving it. One of the papers (Weaver and Roseman) includes a section about genetic introgression, kindly citing my work. Another (Bräuer) claims that it is reasonable to include all Middle Pleistocene humans in Africa and Europe as part of "one polytypic species, Homo sapiens" (Bräuer 2008:32).
So the work of those of us who write about evolutionary mechanisms seems to be making an impact. Still, it's kind of like "dark matter" -- you only know about the ideas because of their effects on what you can read! In this case, you can read a lot of peoples' opinions about these ideas -- you just can't read them from the people who thought of them.
What boring meetings these must be, with everybody agreeing with each other all the time, and nobody to point out all these contradictions!
References:
Bräuer G. 2008. The origin of modern anatomy: by speciation or intraspecific evolution? Evol Anthropol 17:22-37. doi:10.1002/evan.20157
Lieberman DE. 2008. Speculations about the selective basis for modern human cranial form. Evol Anthropol 17:55-68. doi:10.1002/evan.20154
Pearson OM. 2008. Statistical and biological definitions of "anatomically modern" humans: Suggestions for a unified approach to modern morphology. Evol Anthropol 17:38-48. doi:10.1002/evan.20155
Tattersall I, Schwartz JH. 2008. The morphological distinctiveness of Homo sapiens and its recognition in the fossil record: Clarifying the problem. Evol Anthropol 17:49-54. doi:10.1002/evan.20153
Weaver TD, Roseman CC. 2008. New developments in the genetic evidence for modern human origins. Evol Anthropol 17:69-80. doi:10.1002/evan.20161
Who colonized the European Arctic?
I happened across an article by Pavlov and colleagues (2001) about the Mamontovaya Kurya site in the Russian Arctic. From the abstract (64):
The transition from the Middle to the Upper Palaeolithic, approximately 40,000-35,000 radiocarbon years ago, marks a turning point in the history of human evolution in Europe. Many changes in the archaeological and fossil record at this time have been associated with the appearance of anatomically modern humans. Before this transition, the Neanderthals roamed the continent, but their remains have not been found in the northernmost part of Eurasia. It is generally believed that this vast region was not colonized by humans until the final stage of the last Ice Age some 13,000-14,000 years ago. Here we report the discovery of traces of human occupation nearly 40,000 years old at Mamontovaya Kurya, a Palaeolithic site situated in the European part of the Russian Arctic. At this site we have uncovered stone artefacts, animal bones and a mammoth tusk with human-made marks from strata covered by thick Quaternary deposits. This is the oldest documented evidence for human presence at this high latitude; it implies that either the Neanderthals expanded much further north than previously thought or that modern humans were present in the Arctic only a few thousand years after their first appearance in Europe.
An interesting start, that. The archaeology includes a mammoth tusk with marks that may be the result either of deliberate incision or of chopping of other material using the tusk as an anvil. The radiocarbon date of bones and the tusk range between 34,400 and 37,400 years ago.
There are no fossil humans at this site. The authors raise the issue of attribution, noting that the date of the site would mean that modern humans had expanded into the Arctic fringe very shortly after they appeared in Europe.
A pressing question is whether the pioneers who lived in these northern landscapes were members of the ancient Neanderthal population (Homo sapiens neanderthalensis) or newcomers from the south. Most scholars associate the Aurignacian industry -- the more advanced stone-tool technology that appeared in Europe at around 40,000 yr BP -- with the emergence of modern humans. However, the earliest indisputable remains of humans with a fully modern morphology (Homo sapiens sapiens) date to 30,000-35,000 yr BP; that is, well after the archaeologically defined transition from the Middle to the Upper Palaeolithic. In European Russia, well preserved skeletons from the famous Palaeolithic site of Sungir, northeast of Moscow (Fig. 1), show that anatomically modern humans were present there not later than 28,000 yr BP. At the Kostenki IV site on the west bank of the Don river, bones of modern humans have been uncovered from strata dated to 30,000 yr BP. The stone-working technology reflected in the Byzovaya material is similar to that of Sungir and other early Upper Palaeolithic sites of the eastern Szeletien tradition, indicating that these artefacts were manufactured by modern humans. However, whether the person who inflicted the marks on the tusk from Mamontovaya Kurya, as much as 8,000-9,000 years earlier, belonged to the same human lineage as the residents at Byzovaya and other Palaeolithic sites further to the south is more uncertain (Pavlov et al. 2001:66-67, citations omitted).
They also relate the site extensively to the Byzovaya site in the preceding paragraph, noting the archaeology has been classified as "eastern Szeletien with Aurignacian traits" (66).
I remembered Szeletian as a Neandertal-associated "transitional" Upper Paleolithic industry, so I went on a bit of a search to see what the story actually is. The search is not finished yet, as there are some books to consult, but the short answer is that Szeletian means different things to different archaeologists. From Churchill and Smith (2000:75, citations in original):
Most of the various IUP [Initial Upper Paleolithic] cultures of Central and Eastern Europe that are characterized by leaf points have at one time or another been seen as regional variants of the Szeletian, a culture defined at Szeleta Cave in the Bukk Mountains of Hungary (Allsworth-Jones 1990a). Regional distinctions can be identified, however, and the possibility exists as well that the occurrence of leaf points in different regions may be the result, at least in some cases, of convergence (Allsworth-Jones 1990a). Regionally defined leaf-point cultures include the Brynzeny, the Gordineshty, and the Kostenki-Streletsian (Streletskaya) of the Russian Plain (Anikovich 1992), the Altmuhlian of southern Germany, the Jerzmanowician of eastern Germany and Poland, the Bohunician of the Czech Republic (in which leaf points are relatively rare, leading to suggestions that this industry should be considered as a development separate from the Szeletian: Svoboda 1998, 1990), and the Jankovichian (although this might be seen as a Middle Paleolithic industry with leaf points: Gabori-Csank 1990) and the Szeletian sensu stricto of Hungary (see Allsworth-Jones 1990a).
Whoa. At a glance, it sounds like like the Szeletian is defined by leaf points in about the same way that the Aurignacian is defined by split-base bone points, and is therefore just about as unitary -- in other words, it barely hangs together. Like I said, I'm working on understanding this better, but my predilection is to step away from the names and consider the possibility that the "Szeletian" really is a constellation of behaviors weakly if at all linked, and it therefore has no necessary link to biological differences between human populations.
The argument for the Szeletian being the product of the Neandertals is almost entirely based on the similarities between it and the earlier Micoquian industry. There are only two sites with human remains associated with Szeletian assemblages, and neither of these has been clearly shown to be Neandertal in anatomy (the sum total is four teeth from both sites) (Churchill and Smith 2000). The case for archaeological similarity, and the status of the Szeletian as a "transitional" industry, is presented by Valoch (2000):
The situation with the Szeletian is quite different. Even though it is also likely to have been produced by the Neanderthals, the stone industry differes from the Bohunician in completely lacking a Levalloisian component. Typological and technological analyses have shown that the archaic elements of the industry are Micoquian and reflect a technological complex that was widespread in Central Europe. However, the types characteristic of the Upper Palaeolithic are carinated and nosed scrapers and carinated burins -- shapes exclusive to the Aurignacian (Allsworth-Jones 1986, 1990; Oliva 1991, 1992; Valoch et al. 1993). The only type specific to the Szeletian -- the leaf point -- has its origin in the Micoquian. The genesis of such an industry can be explained in only two ways: either it developed as a result of spontaneous substrate evolution (i.e., Micoquian), in which case the different Aurignacian types developed in parallel or almost simultaneously and quite independently of the Aurignacian proper, or the Aurignacian had a share in the formation of the industry through some form of contact with the Micoquian. No other explanation appears viable today, although future studies may produce new information (Valoch 2000:625).
The argument for the eastern Szeletian being the product of modern humans apparently comes from the association with the remains at Sungir. Since these apparently are not necessarily the same cultural tradition as other Szeletian sites (despite the shared name), there seems not to be a conflict.
The implication that the far northern tier of Eurasia was occupied very early by modern humans is another piece of evidence consistent with the idea that the first modern Europeans came from the far north. This hypothesis proposes that the features that people spread into the Palearctic as a rather specialized adaptation, and may have exploited a niche available to highly mobile, long-limbed, and culturally sophisticated people. Ultimately, the eastern extreme of this population may have moved into Beringia and further to the New World.
A list of online resources related to the topic of Paleolithic occupation of the circumarctic is maintained at WorkingDogWeb, which I assume is related because of dogsleds?
References:
Churchill SE, Smith FH. 2000. Makers of the Early Aurignacian of Europe. Yearbk Phys Anthropol 43:61-115. Wiley InterScience
Pavlov P, Svendsen JI, Indrelid S. 2001. Human presence in the European Arctic nearly 40,000 years ago. Nature 413:64-77. Nature
Valoch K. 2000. More on the question of Neanderthal acculturation in Central Europe. Curr Anthropol 41:625.
The bleeding handaxe
National Geographic News' most popular story today is "Odd skull boosts human, Neandertal interbreeding theory."
The NGN article is about a paper coming out in Current Anthropology this month by Andrei Soficaru and colleagues, describing a skull from Pestera Cioclovina, Romania. The skull is between 28,000 and 29,000 radiocarbon years old, and the authors argue that its occipital bone preserves Neandertal-like morphology. The NGN article has some trouble describing the situation, settling for this:
The otherwise human skull has a groove at the base of the back of the skull, just above the neck muscle, that is ubiquitous in Neandertal specimens but has never been seen in the remains of a modern human, argues study leader Erik Trinkaus, an anthropologist at Washington University in St. Louis, Missouri.
"I was frankly quite surprised to see it when I was looking at the specimen," Trinkaus said. "My first reaction was, that shouldn't be there."
The "groove" is a suprainiac fossa, which I can understand is technical, but it's too easy to dismiss things as "a bump here and a groove there" if you ignore the pattern that emerges from which bumps and grooves are there.
Anyway, more on early humans in Europe later. The article ends with an interview with Eric Delson, who is not dismissive but not convinced, either. The final paragraph has this priceless quote:
"But the genetic evidence is not in favor of hybridization, and this fossil does not convince me, nor do the several from Central Europe. I am still waiting for a 'smoking gun,' or perhaps in this case 'a bleeding hand axe.'"
Hmmm....that seems a little like demanding a sign from beyond. I grant, a suprainiac fossa is not exactly stigmata, but hey, a bump here and groove there, and pretty soon you're talking real interbreeding!
The bleeding handaxe. Original photo thanks to Wessex Archaeology, Creative Commons license
Keith on Kent's Cavern
Following up on my earlier post on the Kent's Cavern 4 maxilla: although my library doesn't have back issues of the Proceedings of the Torquay Natural History Society, it turns out that the Center for Research Libraries in Chicago does. So I have acquired a copy of Keith's short report on the Kent's Cavern 4 specimen.
The measurements of the teeth reported by Keith are as follows:
| Tooth | M-D diameter | B-L diameter |
| C | 7.2 | 9.0 |
| P4 | 7.0 | 9.5 |
| M1 | 10.0 | 11.6 |
The teeth are highly worn, and their mesiodistal measurements are therefore suspect due to interproximal wear. Even so, they are not outside the range of other Neandertal specimens. The more accurate buccolingual measurements are at the small end of the Neandertal range but not outside it; two specimens from Hortus match the canine and premolar measurements, as does Saccopastore 2. The M1 measurements are the same as those for Spy 1; the B-L breadth of 11.6 is typical for later Neandertals, matching or exceeding specimens from Hortus, Arcy-sur-Cure, Spy, Engis, and La Quina. The molar is not taurodont; and considering that all the teeth are worn essentially flat without occlusal relief, there is unlikely to be any morphological diagnosis based on the dentition.
From the description, it appears that the lateral view of the maxilla reveals nothing diagnostic, either. Keith reports that "there is preserved a small area of the lower wall of the sinus maxillaris, with the basal part of the zygomatic ridge of the upper jaw" (Keith 1927:1). I'm still hoping to find a picture of that side; my copy did not include Keith's figure.
Keith's diagnosis of the specimen is as follows:
Nor can there be any doubt as to the nature of the individual represented by this fragment: the teeth in their dimensions and characteristics agree in every detail with those from jaws of men of the modern type. And in this type I include, of course, the late palaeolithic peoples of Europe. The teeth and jaw now described may very well have belonged to the same people whose remains have been already discovered in Kent's Cavern -- namely the palate found deep in the upper stalagmite by Mr. William Pengelly, and the other specimen found near the mouth of the cavern and described in the last number of this journal. One can say with assurance that the specimen now described could not be derived from an individual of the Neanderthal type. Further, from the dimensions of the teeth I infer that the individual represented by the specimen was of the male sex and the degree of the wear shown by the crowns of the teeth indicate that he had reached middle life (Keith 1927:1-2).
Keith reports that the specimen is modern, but this is of course in the context of 1927, when Keith and many others believed that modern humans had a long antiquity as Neandertal contemporaries. Thus the not-so-subtle triumphalism associated with every find that appeared to place "modern" humans early in the Paleolithic (the first paragraph of this piece goes to great length to argue for the antiquity of the specimen). The question is not so different today, particularly since this would be the earliest modern human specimen in Europe if it is modern and if the 40,000 year date is accurate. But today we have a broader knowledge of the anatomy of late Neandertals, and this specimen appears to fit within that range as well as the range of modern humans.
Will DNA testing settle the issue? I don't really think so. What does it mean if we find a Neandertal sequence? If the specimen is a modern human at the western edge of Europe 40,000 years ago, what modern human would be more likely to have a Neandertal sequence? Without a strong anatomical case, what is to dispute the hypothesis that this specimen belonged to a population with a mixture of Neandertal and modern morphologies? The same questions could be asked if the date turns out not to be accurate, especially if the prior 31,000 year date was the correct one.
References:
Keith A. 1927. Report on a fragment of a human jaw found at a depth of (10 1/2 ft) 3.2 m in the cave earth of the vestibule of Kent's Cavern. Trans Proc Torquay Nat Hist Soc 5: 1-2.
What is the Kent's Cavern maxilla?
Kent's Cavern, near Torquay, England, underwent systematic archaeological investigation beginning in the 1860's, proceeding intermittently up to the present day. There is a substantial Middle Pleistocene record of human occupation in the cave. The most important fossil human specimen is the Kent's Cavern 4 maxilla, preserving the right canine, third premolar and first molar and the bone holding them together, with a small piece of palate.
Kent's Cavern 4, medial view
According to a story in This Is Devon, new AMS dating by the Oxford Radiocarbon Accelerator Unit has placed the maxilla between 37,000 and 40,000 years ago.
The date should be treated with caution, lying as it does in a time range that is very difficult to date accurately with AMS method. If it is accurate, then the maxilla is older than the Oase fossils from Romania. The key point of interest now is its taxonomy. From the article:
Barry Chandler, assistant curator at the museum, where the jaw bone is currently on display, said the new conclusions posed fresh questions. He said: "If the jaw is anatomically modern - from humans known as Cro-Magnons as Keith believed - then these people spread across Europe, reaching Britain far earlier than is currently thought.
"If, however, Keith was wrong and the jaw is from the human species known as the Neanderthals we will have the first direct evidence of Neanderthals on mainland Britain. We hope to resolve this problem by extracting ancient DNA from one of the teeth."
The Keith (1927) reference is below; I haven't seen it so I don't know what the argument is based upon. Looking at the maxilla, I just don't think there's enough there to make this diagnosis. It should be recalled that Keith's assessment was made during a time when the archaeological sequence was much less established, and there was an active effort to establish the existence of Homo sapiens alongside or previous to the Neandertals. My guess would be that this is a Neandertal; as Churchill and Smith (2000) describe it, there is no compelling association to a specific archaeological industry, so without a strong anatomical case there is no reason to think it is not Neandertal. I have not, however, seen the lateral side of the specimen. If anyone has a lateral or frontal view, I'd be really happy to see it. It could surprise me by being really informative, but even if it was clear whether a canine fossa or maxillary notch may have been present I'm not sure that would be sufficient to prove the specimen is modern.
At the same time, I'm not sure this is the best instance to try taxonomy-by-DNA. In fact, the most interesting possible result (a modern human DNA sequence) would be fundamentally equivocal. Would that mean this was a modern human? Or a Neandertal with a modern human sequence? Or contamination? There is really no way to tell, and that means that only the less interesting result (a sequence clustering with the Feldhofer specimens and other Neandertals) would be informative.
UPDATE: A new BBC story by Paul Rincon gives more details about the dating and potential study of the specimen. The new radiocarbon testing was performed because the old 31,000-year date may have been contaminated by glue applied to the specimen after excavation. There is also this about the Neandertal/modern human assignment:
Further research on the jawbone fragment is planned with the aim of answering this question.
Chris Stringer, of London's Natural History Museum, and Erik Trinkaus, of Washington University in St Louis, US, will carry out a physical examination of the specimen to see if it carries any features diagnostic of either modern humans or Neanderthals (Homo neanderthalensis), their close cousins.
My only concern in this whole thing is the evident unwillingness of anybody to just look at the thing sitting on the museum shelf, until the current redating made it an issue. This is not a snipe against Stringer and Trinkaus at all -- first, because I can think of few better to settle this question, and second because they usually have better things to do than look at every bit of maxilla (albeit one of the only human remains associated with the early Upper Paleolithic in western Europe!). But how many clever British graduate students have there been who could have hopped a train to Torquay and done this observation 10 years ago? 25 years ago?
Let's hope this will make some graduate students consider where they might find the next Kent's Cavern 4.
The Palanth forum has spawned a nice thread on the Kent's Cavern dating, with references and additional information.
If you are interested in the history of the Kent's Cavern excavations, or even in visiting the place itself, there is a very nice virtual tour hosted by the proprietors.
References:
Churchill SE, Smith FH. 2000. Makers of the Early Aurignacian of Europe. Yearbk Phys Anthropol 43:61-115. Wiley InterScience
Keith A. 1927. Report on a fragment of a human jaw found at a depth of (10 1/2 ft) 3.2 m in the cave earth of the vestibule of Kent's Cavern. Trans Proc Torquay Nat Hist Soc 5: 1-2.
Mellars P. 2005. The impossible coincidence. A single-species model for the origins of modern human behavior in Europe. Evol Anthropol 14:12-27.
Kent's Cavern report on the way?
I thought I'd link to this article from This Is South Devon. There aren't any real new details, but it sounds like there may be a report on Kent's Cavern soon:
KENTS CAVERN JAWBONE COULD BE EVEN MORE SIGNIFICANT THAN FIRST THOUGHT
Results of tests on a jawbone excavated from Torquay's Kents Cavern are being eagerly awaited to see if the piece is Britain's first example of Neanderthal remains.
The piece has been analysed by the University of Hull's Centre for Medical Engineering and Technology and all that is awaited now is the findings of a detailed CT scan.
The possibility they're hyping is that KC 4 might be a Neandertal:
The research was initiated when Dr Roger Jacobi and Prof Chris Stringer of the Natural History Museum obtained new radio-carbon dates for animal bones found in cave sediments directly above and below where the jaw fragment was found at Kents Cavern.
These indicated that the layer in which the maxilla was found dates to between 37,000 and 40,000 years ago, and, if the jawbone fragment is a similar age, it would be even more significant than first thought.
If the jaw proves to be Neanderthal, then Kents Cavern will not only be the only place in Britain where there is direct evidence that Neanderthals once lived, but also it would confirm that Neanderthals spread across Europe and reached Britain far earlier than is currently thought.
I wrote about the reanalysis of KC 4 in early 2005, and added a post with Keith's diagnosis of the specimen.
I guess if the date is actually 37,000 or earlier, you have to lean toward Neandertal. The specimen is nondiagnostic, and that date would make it earlier than the current earliest modern Europeans (who are from Romania, a lot farther east than Britain). And metrically it is within the range of Neandertals, as I mentioned:
The teeth are highly worn, and their mesiodistal measurements are therefore suspect due to interproximal wear. Even so, they are not outside the range of other Neandertal specimens. The more accurate buccolingual measurements are at the small end of the Neandertal range but not outside it; two specimens from Hortus match the canine and premolar measurements, as does Saccopastore 2. The M1 measurements are the same as those for Spy 1; the B-L breadth of 11.6 is typical for later Neandertals, matching or exceeding specimens from Hortus, Arcy-sur-Cure, Spy, Engis, and La Quina. The molar is not taurodont; and considering that all the teeth are worn essentially flat without occlusal relief, there is unlikely to be any morphological diagnosis based on the dentition.
Scanning is fun and all, but I really doubt that an internal scan is going to reveal anything diagnostic about the specimen (i.e., outside the range of one or the other possibility). And based on the last couple of years of papers, I would say that finding a modern mtDNA sequence would essentially be a negative result: nobody seems to be willing to say that the presence of a modern sequence can be distinguished from contamination.
So, I suppose it will be a Neandertal -- the first known from Britain. I hope the Torquay Museum puts on an exhibit about how hard it is to tell Neandertals from modern humans -- that would be interesting!
Neandertal introgression, anatomically
I'm just finished with the Neandertal meeting in San Diego, so it's time to decompress a bit. And what better way to do it than some more Neandertal blogging!
It is worth mentioning the paper that finally came out this week about Pestera Muierii, Romania, by Andrei Soficaru, Adrian Dobos, and Erik Trinkaus. Here's the abstract:
The early modern human remains from the Petera Muierii, Romania have been directly dated to 30,000 radiocarbon years before present (30 ka 14C BP) (35 ka cal BP) ("calendrical" age; based on CalPal 2005) and augment a small sample of securely dated, European, pre-28 ka 14C BP (32.5 ka cal BP) modern human remains. The Muierii fossils exhibit a suite of derived modern human features, including reduced maxillae with pronounced canine fossae, a narrow nasal aperture, small superciliary arches, an arched parietal curve, zygomatic arch above the auditory porous, laterally bulbous mastoid processes, narrow mandibular corpus, reduced anterior dentition, ventral-to-bisulcate scapular axillary border, and planoconcave tibial and fibular diaphyseal surfaces. However, these traits co-occur with contextually archaic and/or Neandertal features, including a moderately low frontal arc, a large occipital bun, a high coronoid process and asymmetrical mandibular notch, a more medial mandibular notch crest to condylar position, and a narrow scapular glenoid fossa. As with other European early modern humans, the mosaic of modern human and archaic/Neandertal features, relative to their potential Middle Paleolithic ancestral populations, indicates considerable Neandertal/modern human admixture. Moreover, the narrow scapular glenoid fossa suggests habitual movements at variance with the associated projectile technology. The reproductive and scapulohumeral functional inferences emphasize the subtle natures of behavioral contrasts between Neandertals and these early modern Europeans. (Soficaru et al. 2006:17196).
The paper describes the provenience of the bones -- they are not newly found, but had been originally assumed to be Holocene in age. Recent radiocarbon dating placed them at around 30,000 years old, which makes them among the earliest modern Europeans.
The bottom line is that the bones are modern (i.e., not Neandertal), but they include features that are common in Neandertals. Almost all the other European bones of early Upper Paleolithic date also have Neandertal features. The number and frequency of such features in this earliest Upper Paleolithic sample are greater than in any later sample.
In other words, they look like they have genes from Neandertals. And those genes declined in frequency or effect over time.
Of course for any particular feature on any particular specimen, the story gets more complicated. Take the occipital bun on Muierii 1. It clearly is a projection of the posterior cranium, in the position of the occipital bun in Neandertals, it projects well posterior to inion and it has a fairly abrupt superior aspect. On the other hand, the projection is expressed on a much higher and shorter vault, and certainly doesn't look identical to a Neandertal bun.
But then, Neandertal buns are quite variable, which several Neandertals having no bun at all, and others exhibiting a variable morphology. The ontogeny of the trait probably relates to growth of the posterior brain, the timing of closure of the lambdoidal suture, and the relative bone growth rates of the parietal and occipital bones. Those developmental prerequisites almost certainly differed between skulls with a Neandertal-like cranial shape, and those with a higher, more rounded skull. So the same feature -- or at least, a result of the same developmental process -- may be manifested with different forms in different cranial contexts.
"Contextually archaic" is a nice phrase. It is describing anatomies that occur within modern humans, and that continue to occur within recent and (presumably) living people, but that have become very uncommon. They are far more common in archaic humans, but may have a slightly different pattern of expression, in many cases because the developmental process that generates such features depends on anatomical configurations or events that have themselves changed. So within the context of the sample, they are "archaic" -- reflections back upon earlier humans, in this case Neandertals.
"Neandertal features" certainly has a more intuitive meaning -- features that occur at their highest frequencies in Neandertals -- but it really doesn't convey a lot more information, except for the regional specificity of Neandertals versus all archaic humans elsewhere in the world. But of course since we have many more Neandertals than any other archaic specimens, these "Neandertal features" in some cases are simply "contextually archaic" features in the European context.
What is the point I am coming to? Many "Neandertal features" clearly are more common in early Upper Paleolithic people than in later Europeans, and they show a unidirectional trend toward lower frequencies over time. Some folks would argue that these features don't really demonstrate Neandertal-modern intermixture, because (a) you can't really prove that they are absent in archaic Africans, or they may even be there, although in lower frequencies than Europe; or (b) they are not really the same feature, but instead are consequences of different developmental processes or parallelism.
Why do I think these critiques have little force? Because at this point, we have enough early Upper Paleolithic specimens with such features to notice something very important about them: different specimens have different Neandertal features.
It's like a shotgun approach to Neandertal intermixture. These are not one or two things appearing in parallel, and they aren't chance resemblances in this small early Upper Paleolithic sample, when they almost all decline systematically in later samples.
So when we see each new specimen, like Muierii 1, carrying not only Neandertal features, but its own distinctive set of Neandertal features, that emphasizes the early role of genome-wide intermixture.
However, these traits co-occur with contextually archaic and/or Neandertal features, including a moderately low frontal arc, a large occipital bun, a high coronoid process and asymmetrical mandibular notch, a more medial mandibular notch crest to condylar position, and a narrow scapular glenoid fossa.
Each of these features occurs in other modern specimens, but not in the same combination. And every other specimen from the early Upper Paleolithic with Neandertal or archaic features has a different mix of them. If this phenomenon were the result of parallelism on modern humans entering Europe, or if it were a consequence of features retained from archaic Africans, we should not see this broad and altering mix of features in different specimens.
So bigger samples, adding specimens one at a time, really are important. They let us look at the pattern of variation in ways that test these evolutionary hypotheses.
References:
Soficaru A, Dobos A, Trinkaus E. 2006. Early modern humans from the Pestera Muierii, Baia de Fier, Romania. Proc Nat Acad Sci, USA 103:17196-17201. DOI link
Some chin biomechanics
As an aside from the Neandertal theme, I ran across a paper from earlier this year by Ichim, Swain, an Kieser, where they apply a mechanical model to mandibles with and without chins:
The development of the chin, a feature unique to humans, suggests a close functional linkage between jaw biomechanics and symphyseal architecture. The present study tests the hypothesis that the presence of a chin changes strain patterns in the loaded mandible. Using an anatomically correct 3-D model of a dentate mandible derived from a CT scan image, we analyzed strain patterns during incisal and molar biting. We then constructed a second mandible, without a chin, by 'defeaturing' the first model. Strain patterns of the second model were then compared and contrasted to the first. Our main finding was that chinned and non-chinned mandibles follow closely concordant patterns of strain distribution. The results suggest that the development of the human chin is unrelated to the demands placed on the mandible during function.
There's a long literature on chin biomechanics (notably, including Tim White's dissertation!), and if you're interested you probably already know it. (If you're interested and don't already know it, there's still hope for you!)
So I really have no comments; just a note to point this one out.
References:
Ichim I, Swain M, Kieser JA. 2006. Mandibular biomechanics and development of the human chin. J Dent Res 85:638-642. Abstract
Maybe Chinese fire drills explain the date discrepancies
I noticed that the cover of the most recent New Scientist is a story about modern human origins by science writer Dan Jones. It's headlined, "Going global: how humans conquered the world."
I think Jones has done a nice piece of work here -- at 2700 words, the story is easy to read, and it illuminates a certain kind of current consensus. It touches on everything from the Herto hominids, to the Blombos The underlying theme is the idea of a "coastal route" dispersal of modern humans from Africa, coupled with some detail about Paul Mellars' Afro-Indian connection, Spencer Wells' Y-chromosome story, the early Herto and Omo Kibish remains, the relevance of Oase and Tianyuan to early dispersal scenarios, and the "megadroughts" of the African Late Pleistocene.
I'll tell you one thing: The piece succeeds at making me feel like a member of the Neandertal Underground, standing on the side of the road as the march of the "Human Revolution" goes by.
The thing is that none of these separate elements fit together. It's not hard to figure that tracing the Y chromosome genealogy of Eurasia to a divergence in the Middle East 40,000 years ago doesn't match up very well with the idea of an "early coastal route dispersal" 60,000 years ago, or an initial colonization of Australia 50,000 years ago. Placing "modern human anatomy" earlier and earlier in time -- back to 200,000 years ago -- isn't exactly helping to explain the behavioral record in the last 70,000 years. And the archaeology that places "modern human behavior" increasingly into the Middle Stone Age doesn't explain why the same behaviors should be found in Neandertals.
Sometimes the contradictions are so glaring that Jones almost can't help but juxtapose them:
"The similarities between Africa and India are not coincidental, and fit in beautifully with the DNA evidence," says Paul Mellars, an archaeologist at the University of Oxford. Although none of these artefacts is more than 35,000 years old, that may simply reflect the fact that sea levels are about 100 metres higher today than they were 50,000 years ago. Any artefacts or bones left by the first coastal migrants are now buried beneath the sea.
I never credit someone with quotes taken from a news article -- every nuance of the evidence is simply not that important to the casual reader. But it's sort of obvious that some of the DNA evidence poses a problem here. And the dates are entirely discordant.
Mellars has emphasized in print (e.g., 2006) the material similarities between early Upper Paleolithic assemblages of India and the Howieson's Poort industry of Africa. The similarities are there, but the dates are quite different. "Lower sea levels" is only arm-waving: Sure, the lack of earlier evidence of similar industries is a problem, but a much bigger problem is explaining the 40,000-year persistence of these "similar" industries in the constant adjacent presence of other patterns of material culture.
The obvious alternative is that the similarities are coincidental -- or at least don't reflect a lineal cultural relationship between 70,000-year-old Africans and 30,000-year-old Indians. That doesn't argue against dispersal: after all, the abilities represented by the material remains may have dispersed, early or late, even if the tools themselves didn't.
But we should also consider the similarities with the cultural remains of late Neandertals and even earlier peoples of Europe, including the pigment use, engraved lines, pendant drilling and blade manufacture.
What we have here is a clown car of a hypothesis: everything thrown in but the bearded lady. No hypothesis is ever tested: Consistency rules. This is no discredit on Jones at all, who clearly does the best job possible of fitting together all these recent papers. The problem is that when you see them all next to each other, you can't help but see that these 115,000-year-old Eritrean shellfish, 40,000-year-old Y chromosome divergences, 65,000-year-old mitochondrial haplogroups, 30,000-year-old Indian blades, 35,000-year-old Romanian skeletons, 70,000-year-old ochre engravings, and 190,000-year-old African skulls really can't fit together to tell a story of a single human dispersal at a single time.
Either the hypothesis is wrong, or some of the data are. Or both.
References:
Jones D. 2007. Going global: how humans spread across the world. New Scientist, Oct. 27, 36-40.
Mellars P. 2006. Going east: new genetic and archaeological perspectives on the modern human colonization of Eurasia. Science 313:796-800. doi:10.1126/science.1128402
"Not so fast, says one anthropologist"
Hawks sightings in the news.
I've been in the midst of a grant proposal -- yes, I actually do write those from time to time! Yes, you can support the site by giving my grant proposals glowing reviews...
Anyway, there hasn't been much time for me to follow up on that "Skull study deals death blow to multiregional evolution" story that's been going around this week. But I've written a few notes:
The two "out of Africas"
Another of the craniometric stories going around this week (Discovery News) proposes that early Levantine modern humans (Skhul-Qafzeh) and Pleistocene Australians come from an early out-of-Africa dispersal that was later mostly replaced by true modern humans (represented by Upper Paleolithic Europeans and living people everywhere). The study is by Michael Schillaci; here's the abstract:
This study examines the genetic affinities of various modern human groupings using a multivariate analysis of morphometric data. Phylogenetic relationships among these groupings are also explored using neighbor-joining analysis of the metric data. Results indicate that the terminal Pleistocene/early Holocene fossils from Australasia exhibit a close genetic affinity with early modern humans from the Levant. Furthermore, recent human populations and Upper Paleolithic Europeans share a most recent common ancestor not shared with either the early Australasians or the early Levantine humans. This pattern of genetic and phylogenetic relationships suggests that the early modern humans from the Levant either contributed directly to the ancestry of an early lineage of Australasians, or that they share a recent common ancestor with them. The principal findings of the study, therefore, lend support to the notion of an early dispersal from Africa by a more ancient lineage of modern human prior to 50 ka, perhaps as early as OIS 5 times (76-100 ka).
But the Skhul-Qafzeh sample and the Pleistocene Australia + Wadjak sample used in the paper (a subset of all the actual specimens) are all males, and the Upper Paleolithic Europeans and recent skeletal samples are (as you might expect) half female.
Seems like a problem....
References:
Schillaci MA. 2008. Human cranial diversity and evidence for an ancient lineage of modern humans. J Hum Evol (in press) doi:10.1016/j.jhevol.2007.10.010
John Hawks Department of Anthropology
University of Wisconsin—Madison
Copyright © 2007 John Hawks