Paul Mellars is enjoying a rather prolific year, as far as publishing review papers in high-profile journals is concerned. The latest one can be found in Science and concerns the archaeological evidence from southern Asia between 50 and 30,000 BP. Unsurprisingly, Mellars argues that these artifacts provide indisputable evidence for the dispersal of (not to say the colonization of the Old World by) anatomically and behaviorally modern humans. Now, there's things I like about this papers, and things I dislike.
On the “like” side, Mellars present evidence from an area that is largely unknown (and therefore undiscussed) by most researchers concerning themselves with modern human origins research. This therefore exposes the rest of the discipline to data that offer the potential to confirm or contradict current ideas and models. This is done in his usual concise and engaging style, which is not something that is given to all paleoanthropologists to be able to do.
On the “dislike” side, Mellars once again (see Mellars 2006a) implicitly presents archaeology as simply an ancillary line of evidence to be at worst fitted to or at best compared to the conclusions reached by seemingly serious disciplines like evolutionary genetics and human paleontology (see discussion in Marks 2003). This, in my view, seriously demeans archaeology as an independent field of study which has a lot to offer. I think part of why Mellars perhaps unwittingly depicts archaeology in such a way has to do with his approach to archaeology. For him, archaeology is largely a culture-historical exercise, meaning that the goal of archaeology is to track the extant and duration of given “cultures.” From this perspective, artifacts are not so much objects that were used by prehistoric hominins to achieve given ends but signals of group identity. In this sense, a Dufour bladelet, say, becomes simply the Paleolithic equivalent of a coin of a given age and provenience in numismatics.
As I've said before, this is not inherently wrong, and some artifacts unquestionably have restricted temporal and geographical distributions. However, this perspective stands in stark contrast to the goals of anthropological archaeology and evolutionary ecology, which are to understand how people acted in the past and why. For anyone interested in evolutionary processes in the deep past, these are the questions that should matter. To simply plot the distribution of culture groups does nothing to explain the evolutionary storyline to which they belong, it merely sets the stage. It's like stating that a book comprises X number of chapters without explaining how the chapters are related and why one chapter comes to a close when and how it does. To me at least, this is very unsatisying.
Getting back to the paper itself, however, there are some more serious issues with some of Mellars' assertions. As concerns the genetic evidence for a single population diffusing from Africa, he brushes aside known problems with studies of mitochondrial and Y-chromosome DNA that potentially support the existence of two separate populations despite citing fully eight such critiques, which is no small number considering that he cites only seven studies in support of his argument. This is not necessarily critical, since studies are liable to criticisms even if they are not thoroughly flawed, but these numbers do give pause.
As far as the archaeology is concerned, Mellars makes his case for a direct link between Africa and southern Asia by presenting evidence that a handful of sites dated to between 30-34 kya (calibrated, which means roughly 27-31 kya uncal, which corresponds to the beginning of the Gravettian and not the Aurignacian in Europe!!) yielded “crescentic” forms and ostrich eggshell beads similar to a handful of African Howiesons' Poort (and Howiesons' Poort-like) assemblages dating to at most 65 kya. In passing, Mellars once again repeats his assertion that such lithics may have been parts of arrows, something which I have shown to be unsupported by any hard evidence in two previous posts (the first, the second). As concerns the lithics, the argument for analogy is unconvincing on two levels. On a purely empirical level, a casual inspection of the drawings of them presented by Mellars suggests that the majority of the southern Asian artifacts were made on flake blanks, which is a very different way to manufacture crescentic forms than the backing of blade segments that characterizes the African material. Further, Mellars presents no data whatsoever about the rest of the lithic assemblages to which these crescents belong. In the Howiesons' Poort of Klasies River Mouth, Wurz (2002) has shown “crescents” are present in the hundreds! They thus represent a central part of the assemblage. Unless the lithic assemblages from southern Asia can be shown to display a similar dependence on crescent technology, any argument about whether they represent the same “culture” or even more simply the same “way of doing things” is unsupported. Otherwise, one would have to say that the Uluzzian of southern Italy, which Mellars himself has repeatedly and unwaveringly assigned to Neanderthals (e.g., Mellars 1996, 2004, 2005), would have to be taken as proof positive of modern human expansion in that part of the world as well.
On a conceptual level, it is also very interesting to take a look at how Mellars attempts to present the case for a cultural connection between Africa and southern Asia. Rather than presenting any contextual data about the assemblages which he mentions, he limits himself to presenting composite pictures of “representative” artifacts from, on one side, southern Asia and, on the other, Africa. It doesn't matter that in both instances the assemblages invoked are separated by hundreds if not thousands of years and kilometers. A telling analogous argument is that put forward by Bradley and Stanford (2004) which alleges that the Clovis Paleoindian culture of North America derives from the influence of western European Solutrean migrants who would have crossed the Atlantic to settle the Americas. This argument has been debunked in press by a number of paleoanthropologists (e.g., Sellet 1998, Straus 2000, Clark 2004) and does not appear – to the best of my knowledge – to enjoy widespread credence among the archaeological community as a whole. Interestingly in the context of this discussion of Mellars' latest paper, however, in their latest paper Bradley and Stanford's discussion of actual artifacts is illustrated only by a set of three figures (2004:466, 467, 468) in which they present, on the one side, select Clovis artifacts and, on the other, Solutrean artifacts. Here too, there are no detailed discussions of the broader context in which these lithics are found, and no solid empirical data presented in tables to back up their argument. Rather, the similarities between the composite pictures are, in this case as well, argued to represent indisputable evidence of a direct link between the two. Except that in this case, nobody else no seems to be convinced, beyond perhaps the popular press which is always so eager to present “both sides of the debate.”
As Clark (2004:110-111) argues:
“Their scenario is an example of post hoc accomodative argument, wherein explanations are developed after an analysis has been completed (in this case, a very superficial one) to account for patterns detected in a data set. Post hoc accomodation is a weak form of inference because the research designs that incorporate it lack a deductive component... Post hoc accomodative argument sets the agenda for future research, rather than constituting a set of conclusions that can stand or fall on their own.”
I think that this relatively fairly describes the gist of Mellars' approach as well. Now, I'm not saying that post hoc accomodative arguments cannot be a good source of ideas, some of which may even be amenable to empirical testing. However, in this case, there is very little analytical depth to this and Mellars' other recent papers (2006a, 2006c), and no critical take on the data. Rather, Mellars repeats the same argument over and over again, incorporating only the data that fits his ideas. The problem is that such papers are then taken as gospel by other researchers who cite it as proof for a single-origin colonizing population of modern humans that blazed an ochre-stained trail out of their African homeland as they marched ineluctably to conquer the rest of the world. Contemporary archaeology can – and most importantly should – do more than this, and develop its own set of conclusions that can then be confronted to the human paleontological and genetic records rather than vice-versa.
Bradley, D., and D. Stanford. 2004. The North Atlantic ice-edge corridor: a possible Palaeolithic route to the New World. World Archaeology:459-478,
Clark, G. A. 2004. Deconstructing the North Atlantic connection. In The Settlement of the American Continent (C.M. Barton, G.A. Clark, D.R, Yesner, and G.A. Pearson, eds.), pp. 103-122. The University of Arizona Press, Tucson.
Marks, A. E., 2003. Reflections on Levantine Upper Palaeolithic studies: past and present. In More than Meets the Eye: Studies on Upper Palaeolithic Diversity in the Near East (A. N. Goring-Morris & A. Belfer-Cohen, eds.), pp. 249-264. Oxbow Press, Oxford.
Mellars, P. 1996. The Neanderthal Legacy. Princeton University Press, Princeton.
Mellars, P. 2004. Neanderthals and the modern human colonization of Europe. Nature 432:461–465.
Mellars, P., 2005. The impossible coincidence. A single-species model for the origins of modern human behaviour in Europe. Evolutionary Anthropology 14, 12–27.
Mellars, P. 2006a. Why did modern human populations disperse from Africa ca. 60000 years ago? A new model. Proceedings of the National Academy of Sciences 103:9381-9386.
Mellars, P. 2006b. Going east: new genetic and archaeological perspectives on the modern human colonization of Eurasia. Science 313:796-800.
Mellars, P. 2006c. A new radiocarbon revolution and the dispersal of modern humans in Eurasia. Nature 439:931-5.
Sellet, F. 1998. The French connection: investigating a possible Clovis-Solutrean link. Current Research on the Pleistocene 15:67-68.
Straus, L.G. 2000. Solutrean settlement of North America? A review of reality. American Antiquity 65:219-226.
Wurz, S. 2002. Variability in the Middle Stone Age lithic sequence, 115,000–60,000 years ago at Klasies River, South Africa. Journal of Archaeological Science 29:1001–1015.