Snakes!!!

Yesterday's Science Daily contains a report based on a new paper by Lynne Isbell in the Journal of Human Evolution. In it, she argues that "that primates developed good close-up eyesight to avoid a dangerous predator -- the snake." In Isbell's words: "A snake is the only predator you really need to see close up. If it's a long way away it's not dangerous."

I haven't yet had time to read the paper thoroughly, but the basic idea is certainly an interesting one, and seems concordant with at least some aspects of the fossil record.

If this is true, it may also explain in part why so many people are absolutely terrifed of snakes... it may also help explain the current buzz (which sometimes borders on obession) surrounding the upcoming releason of the movie "Snakes on a Plane" starring Samuel L. Jackson!

References:

Isbell, L. A. 2006. Snakes as agents of evolutionary change in primate brains. Journal of Human Evolution 51:1-35.

Paleolithic interstratifications: some thoughts

Reading a summary paper by Ludovic Slimak (2005), I was very interested to learn about the stratigraphy of the site of Grotte Mandrin in the Rhône Valley of southeastern France. Slimak mentions that the site contains a level assigned to the Neronian (defined by laminar blank production schemes and Soyons point production), which can be seen as ‘transitional’ sensu lato since it marks a dramatic departure from traditional Late Mousterian patterns in the region (see Slimak 2004 for a full treatment). The most interesting aspect of the Grotte Mandrin sequence, however, is that while the Neronian has been identified in other neighboring sites, at Mandrin it overlies typical Mousterian deposits and is itself overlain by not one, not two but fully five Mousterian levels.

This means, in effect, that we are dealing with a credible case of paleolithic interstratification. The issue of Late Pleistocene interstratifications has been a hot topic of late, especially since the publication of a paper by d'Errico and colleagues (1998) in which they suggested that the Châtelperronian was completely independent from the Aurignacian. This is in contrast to a widely held view that saw the Châtelperronian as resulting from the acculturation of Mousterian-making Neanderthals by Aurignacian-making modern humans (e.g., Mellars 1996, 2005). From that perspective, the existence of Châtelperronian-Aurignacian interstratifications demonstrated that the two cultures had occupied a common territory close enough in time to support potential scenarios of contacts between the two populations.

In recent years, however, not one such claimed interstratification has survived critical scrutiny: The cases from Roc de Combe and Le Piage were shown by J.-G. Bordes (2003) to be the results of postdepositional processes, while the case from El Pendo was long ago recognized to be unconvincing (Hoyos and Laville 1982; see Zilhão and d'Errico 1999 for a detailed review). Likewise, the putative case for interstratification at Grotte des Fées de Châtelperron recently postulated by Gravina et al. (2005) has not survived empirical and theoretical scrutiny (d'Errico et al. 2006, Riel-Salvatore et al. 2006).

Thus, the Grotte Mandrin interstratification indicates that while interstratifications do occur in the Late Pleistocene Eurasian archaeological sequences, they seem to document only interstratifications between industries made by Neanderthals. In fact, while there are no diagnostic remains associated with the Neronian, Slimak (2004, 2005) shows that, on technological grounds, this industry shows affinities more to the Mousterian than to the proto-Aurignacian of the region, which was putatively made by modern humans. The only other Mousterian-'transitional industry' interstratification case of which I am aware is that of Buran-Kaya III, in Crimea, where a Micoquian Mousterian of Kiik-Koba tradition dated to ca. 28kya uncal. BP overlays an Early Upper Paleolithic industry described as either a Early Streletskayan (Marks and Monigal 2000, Hardy et al. 2001) or Eastern Szeletian (Chabai 2000). And, as stated by Hardy et al. (2001:10973) “Diagnostic human remains are not known from the Streletskayan levels, but similar initial Upper Paleolithic levels in central and western Europe have yielded only diagnostic Neandertal remains,” which suggests that it also was the handiwork of Neanderthals.

In other words, what we see in the Eurasian archaeological record is that when transitional industries loosely defined are found interstratified, they are only interstratified with regional Mousterian assemblages. In most cases, however, transitional industries – when they are found – usually only overlie the Mousterian and underlie the local facies of the Aurignacian (whose integrity is another issue altogether). This conclusion has several implications. First, it argues strongly against the acculturation scenario because there are no transitional-Aurignacian interstratifications anywhere. As well, it argues against it, because the Mousterian rather than its supposedly acculturated forms was able to reinstall itself in those areas where Mousterian-transitional interstratifications are documented, implying that the Mousterian was a better practical solution to the rigors of paleolithic life than any of the Early Upper Paleolithic industries.

To a degree, it also argues against (or at the very least nuances) the “indigenist” perspective, because it demonstrates that, if 'transitional' industries represent an independent Neanderthal development of Upper Paleolithic adaptations, that process was not linear everywhere, and that in certain cases Mousterian adaptations must have been preferable to Upper Paleolithic ones, despite the oft-claimed advantages provided by all the material traits that define the latter period (e.g., Bar-Yosef 2002, Mellars 2005). I would surmise that – precisely because these alleged advantages have never been assessed empirically – this may simply demonstrate that a trait-based approach to the definition of “modern” behavior is, for the present at least, doomed to be unsatisfactory from an evolutionary perspective.

There are alternative models, namely those postulating a 'mosaic' pattern of biocultural evolution, that account rather well for this pattern of interstratification, but for various reasons, they have been receiving progressively less and less currency in academic discussions about the disappearance of Neanderthals (Clark 2002, Marks 2003, Straus 2003). There's a number of potential reasons behind that recent lack of attention, but they are another topic altogether. In any case, because this perspective postulates that the disappearance of Neanderthals was a process that unfolded variously in various social, demographic and ecological contexts, it can accommodate the patterns just described rather well, as well as providing an explicit theoretical framework according to which to approach the question of the Middle-Upper Paleolithic transition. Briefly put, this framework is that, because it fully acknowledges that Neanderthals eventually disappeared without assuming that they were necessarily directly replaced by competing populations of modern humans, it sets the scene for the articulation of explicit models of what factor(s) might have played a determinant role in this process. Thus, for one thing, it presents Neanderthals as active agents in the process that led to their eventual disappearance from the human paleontological record, as opposed to the passive or at best reactive agents of traditional replacement scenarios. It also forces researchers to take a more particularistic approach to the question rather than focusing only on the big picture and brushing inconvenient data aside in order to make a region's record fit the expectations of the traditional replacement model.

The question of interstratifications is an important one, but it has unfortunately so far not received as much attention as it should have, especially from the perspective of site formation processes. What we are seeing in the archaeological record of the Late Pleistocene are not, after all, single occupation events by hominins. Rather, almost all archaeological assemblages are time-averaged signatures of repeated occupations of a localities, and they therefore only capture the gross overall behavioral tendencies employed by prehistoric foragers rather than specific moments in time (although such assemblages admittedly do occur very occasionally). As such, it is difficult to imagine how Paleolithic assemblages could effectively monitor acculturation, which is a process that tends to take place rather abruptly and completely. In most cases, acculturation over the long term (which is what archaeological deposits measure) does not result in a 'mix' of features but rather in the replacement of the 'receptor' culture. This is demonstrated by cases such as the Numic expansion in the American Great Basin or the Thule expansion in the Arctic, both of which took about a millennium to unfold and where both cultures simply overtook the preceding ones, without the creation of 'hybrid' material cultures over the course of these processes.

This means that when we find a peculiar archaeological industry interstratified between others, what we see is that for an interval spanning centuries or even millennia, that industry proved to be the best adaptation to the context of the site over that period. In turn, this implies that it probably had distinctive ways of exploiting a given environment, working better at some things than other prehistoric industries. This is quite a different perspective from that which sees an industry present only as one level in the midst of others attributed to another industry as the passive reaction of the original industry to forces beyond it control.

Whatever the case may be, the issue of interstratifications and their meaning is far from resolved. However, with the realization that the only known interstratifications now concern only 'transitional' industries and the Mousterian, we're at a crossroad of sorts where we must reexamine what are our expectations of this phenomenon and explicitly state how it would fit within the theoretical perspectives espoused by various researchers. And with an explicit theoretical reevaluation, there should also come a delineation of what the best methodological approaches to documenting interstratifications should be.

References:

Bar-Yosef, O. 2002. The Upper Paleolithic revolution. Annual Review of Anthropology 31:363–93.

Bordes, J.-G., 2003. Lithic taphonomy of the Châtelperronian/Aurignacian interstratifications in Roc de Combe and Le Piage (Lot, France). In The Chronology of the Aurignacian and of the Transitional Technocomplexes: Dating, Stratigraphies, Cultural Implications (J. Zilhão & F. d’Errico, eds.), pp. 223-244. Instituto Português de Arqueologia, Lisbon.

Chabai, V. P. 2000. The Late Middle and Early Upper Paleolithic in Crimea (Ukraine). In Les premiers hommes modernes de la Péninsule Ibérique, Actes du Colloque de la Commission VIII de l'UISPP (J. Zilhão, T. Aubry & A. F. Carvalho, eds.), pp. 25-35. Instituto Potuguês de Arqueologia, Lisbon.

Clark, G. A. 2002. Neandertal archaeology: implications for our origins. American Anthropologist 104:50–67

d'Errico, F., J. Zilhão, M. Julien, D. Baffier, and J. Pelegrin. 1998. Neanderthal acculturation in western Europe? A critical review of the evidence and its interpretation. Current Anthropology 39:S1-S44.

d'Errico, F., J.-G. Bordes, A. Lenoble, and J. Zilhão. 2006. No Neandertal/early modern
human interstratification at the Châtelperronian type-site. Paper presented at the 2006 Annual Meetings of the Paleoanthropology Society, San Juan, Puerto Rico.

Gravina, B., P. Mellars, C. Bronk Ramsey, 2005. Radiocarbon dating of interstratified Neanderthal and early modern human occupations at the Châtelperronian type-site. Nature 438:51-6.

Hardy, B.L., M. Kay, A. E. Marks, and K. Monigal. 2001. Stone tool function at the paleolithic sites of Starosele and Buran Kaya III, Crimea: behavioral implications. Proceedings of the National Academy of Sciences 98:10972-7.

Hoyos, M., and H. Laville. 1982. Nuevas aportaciones sobre la estratigrafia y sedimentologia de los depositos del Paleolitico Superior de la Cueva de El Pendo (Santander): Sus implicaciones. Zephyrus 34-35: 285-293.

Marks, A. E., and K. Monigal. 2000. The Middle to Upper Paleolithic interface at Buran-Kaya-III, Eastern Crimean. In Neanderthals and modern humans— discussing the transition: central and eastern Europe from 50,000–30,000 BP (J. Orschiedt & G. C. Weniger, eds.), pp. 212-226. Neanderthal Museum, Mettmann.

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. 2005. The impossible coincidence. A single-species model for the origins of modern human behaviour in Europe. Evolutionary Anthropology 14:12–27.

Riel-Salvatore, J., A. E. Miller, and G. A. Clark. 2006. On the reality of a claimed Châtelperronian-Aurignacian interstratification at Grotte des Fées de Châtelperron (Alliers, France). Paper presented at the 2006 Annual Meetings of the Paleoanthropology Society, San Juan, Puerto Rico.

Slimak, L. 2004. Les dernières expressions du moustérien entre Loire et Rhône. Thèse de doctorat, Département Histoire de l'Art et Archéologie, Université de Provence.

Slimak, L. 2005. Entre deux mondes, les derniers Néandertaliens en moyenne vallée du Rhône. Ardèche Archéoologie 22:1-7.

Straus, L. G. 2003. “The Aurignacian”? Some Thoughts,” in The Chronology of the Aurignacian and of the Transitional Technocomplexes: Dating, Stratigraphies, Cultural Implications (J. Zilhão & F. d’Errico, eds.), pp. 11-18. Instituto Português de Arqueologia, Lisbon.

Zilhão, J., and F. d'Errico. 1999. The chronology and taphonomy of the earliest Aurignacian and its implications for the understanding of Neandertal extinction. Journal of World Prehistory 13: 1-68.

Forager mobility, measured.

P. Jeffrey Brantingham has a new paper in the June 2006 issue of Current Anthropology in which he proposes a formal model to estimate forager mobility based on lithic raw material incidence in an assemblage. The paper is based largely on the development and testing of a model using a stochastic process called a Lévy random walk, followed by a short section which compares the expectations of the model to the Early Upper Paleolithic archaeological record from southwest France. Brantingham's theoretical perspective is grounded in human behavioral ecology and the approach he employs here derives from various the forms of optimality models that have become part and parcel of this field of study over the past quarter century (Winterhalder and Smith 2000). The math involved in building the model is rather involved but nonetheless imminently understandable, and Brantingham is explicit about the assumptions that underlie the model. In essence, he is trying to hold everything else constant in order to see how mobility alone influences raw material composition in an assemblages, so as to subsequently permit the utilization of that variable as a way to infer prehistoric mobility

I'm generally not too big a fan of the CA comment format because I think it lends itself too easily to veiled personal attacks and forces an unnecessarily polemical tone into scholarly discussion. However, here, it works quite well, with the commentators adopting a level-headed tone and providing constructive criticism on the paper. As a whole, they reasonably highlight the limitations that an archaeological record that is by nature incomplete and a time-averaged reflection of human behavior may have on the applicability of aspects of the model, problems which Brantingham acknowledges but leaves for future studies, a very reasonable position given the complexity of this first step in the process.

In my opinion, this is exactly the kind of work that needs to be done in hunter-gatherer archaeology, in order to move the filed forward, because it generates testable expectations that can be compared to pattern in the archaeological record. This does two things: First, it allows the identification of broad principles according to which specific facets of human behavior are (or can be) structured. Second, any discrepancies between expected and observed patterns (which are almost unavoidable) then lend themselves to further explorations and discussion, thus highlighting the virtually unlimited range of case-specific adaptive strategies humans and their ancestors devised to maximize their fitness and well-being in the past.

That said, I do have some minor reservations on some of the assumptions made by Brantingham's model. For one thing, while it may be necessary to assume this for conceptual simplicity, it is unreasonable to consider lithics simply as units of raw material. Of course, on one level, that is exactly what they are, so some might say this is warranted. However, humans have no inherent need for rock. What they have need for are the tools (broadly defined here) that are made from rock. As such, different types of lithics have different functions and different kinds of use-lives which may vary in length and nature. This argument complement those of commentator Michael Shott, although one can see how this facet of forager life could rather simply be incorporated in future refinements of Brantingham's model. My second reservation may betray my unfamiliarity with formal modeling or my misunderstanding of a specific aspect of Brantingham's model, but while I understand how he uses a Lévy random walk to generate distance-from-source distance rates, I'm not sure how these correspond to human-scale features. For instance, while I understand that lithic discard (and acquisition) may be constant in time and space, archaeologists and ethnographers mainly rely on 'sites' as the unit of analysis on which an assemblage is tied to a archaeological or ethnographic landscape. While the Lévy random walk generates patterns of distance-to-source discard rates, I'm unsure as to how these relate to sites writ large. In other words, does a Lévy random walk generate points on the landscape where more than single units of raw material are discarded or is each discard point completely independent? If the latter is true, then how do we reconcile Brantingham's model's observations about the expected patterns of raw material discard to the human reality where specific spots are the locus for multiple discard instances of raw material units? Again, this can probably be incorporated in the formal model rather easily, but it did make me ponder the one-to-one comparability of the model's patterns to what we document archaeologically.

Now, these interrogations aren't meant to detract from the value of Brantingham's paper. In fact, I think that it's exemplary in terms of how it links theory to methods, clearly explains the methods, and then compares expectations to archaeological data. Brantingham cites a number of other studies that are adopting formal modeling as a central methodological tool, so it looks as though the days of 'common-sense' approaches to defining expectations about the archaeological record may thankfully be drawing to a close, to be replaced by more rigorous research perspectives that lend themselves to direct testing.

References:

Brantingham, P. J. 2003. A neutral model of stone raw material procurement. American Antiquity 68:487–509.

Brantingham, P. J. 2006. Measuring forager mobility. Current Anthropology 47:435-459.

Winterhalder, B., and E. A. Smith. 2000. Analyzing adaptive strategies: human behavioral ecology at twenty-five. Evolutionary Anthropology 9:51-72.

Troppo bello!!!!!

I-TA-LIA!!!
I-TA-LIA!!!
I-TA-LIA!!!
I-TA-LIA!!!

24 years of waiting are over! What a scene it was in MTL last night, I can only imagine what it was like in Italy!Now that it's all over, though, back to (more) serious matters...

"Hobbit"-o-rama!

Debbie Argue and colleagues have a new paper in press in the Journal of Human Evolution about the Liang Bua 1 specimen that, well, argues that LB1 does, in fact, represent a specimen of a distinct species rather than either a microcephalic or 'pygmoid' Homo sapiens individual. Their case is based on an evaluation of the physical characteristics of documented cases of various forms of microcephaly and dwarfism, as well as those of pygmoid individuals in the literature, including one from Flores. They conclude that beyond a small cranial capacity, the LB1 specimen shares almost nothing in common morphologically with microcephalic humans. Overall, their argument is well structured and relatively expansive, covering as it does both cranial and postcranial characteristics, and including a wide range of comparative datasets, although some of them (especially the microcephalic modern humans, with only two specimens) are pretty sparse quantitatively. As they state themselves, “Microcephaly is an extremely heterogeneous condition and, while our results are suggestive, it may be that they would differ should a larger sample of microcephalics be studied” (Argue et al. 2006: ms. p. 20). I'm sure defenders of the alternative positions about the specific status of the Liang Bua remains will promptly have more to say about these data and the resulting analysis, however, so keep posted.

To me, however, perhaps the most interesting aspect of the paper is the scenario about the evolutionary history of H. floresiensis, since Argue et al. don't believe that it descended from Asian H. erectus, which had been held as a potential ancestor for H. floresiensis. Rather, they propose a number of alternative evolutionary scenarios which mention as a possible ancestor an Australopithecine-like or unknown early Homo species that would have diffused out of Africa by ca. 2 mya. As the authors themselves acknowledge, however, there remains to explain just how that ancestral population would have reached Flores and subsequently become genetically isolated. The idea, which Argue et al. mention, that they might have “washed ashore” strikes me as very unlikely. There would have been a need for a population of those critters to be flung there by the seas in order for it to be genetically viable, which is hardly a likely scenario in my opinion. Importantly, they also raise the question of why hominins stuck on Flores should have necessarily become dwarfed, since the island hardly qualifies as a “predator-free environment,” at least for hominins. This, however, also raises the question of why Stegodon should have become dwarfed if they were predated by technologically-able hominins like LB1 who might have been on the island for almost two million years.

From a purely archaeological perspective, this paper raises some interesting issues, too. First, it implies that whoever settled on Flores had some kind of seafaring ability, no matter how rudimentary. Conversely, it implies that modern humans, who were almost certainly in the area by about 60kya and had seafaring capacities, did not for some reason settle Flores for almost 50,000 years! Given the short thrift most archaeologists seem to think modern humans gave the Neanderthals, (and who occupied almost the whole of Eurasia!), it seems unlikely that the “fearsome local” scenario would make much sense for Flores, especially since modern human hunter-gatherers were on the island by ca. 10Kya anyway, with much the same technology as modern hunter-gatherers of the region had by 60kya. Secondly, if Flores was reached ca. 2 mya by the direct ancestors of the Linag Bua specimens, it implies that there should be a complete Oldowan-to-blade-technology technological strategy (or something similar) documented in the archaeological record of the island. The recent paper by Brumm et al. (2006) certainly provides evidence for one potential point along that continuum (although their case for any “technological continuity” on Flores between 800-12 kya certainly is far from solid – I intend to post more on this later), but one would expect both older and, so to speak, coarser lithic technological strategies to be documented on the island. These concerns, of course, presuppose that Argue and colleagues are right, something which only time will tell. However, as in all paleoanthropology, these questions demonstrate that it is imperative, when formulating evolutionary scenarios, to integrate all facets of prehistoric hominin life, both morphological and archaeological. As it is, until we also get data that would enable a discussion of those archaeological questions, there is still a lot to be done in order to demonstrate that Homo floresiensis is indeed a separate species.

References:

Argue, D., D. Donlon, C. Groves, R. Wright. 2006. Homo floresiensis: Microcephalic, pygmoid, Australopithecus, or Homo? Journal of Human Evolution doi: 10.1016/j.jhevol.2006.04.013 (in press).

Brumm, A., F Aziz, G. D. van den Bergh, M. J. Morwood, M. W. Moore, I. Kurniawan, D. R. Hobbs, and R. Fullagar. 2006. Early stone technology on Flores and its implications for Homo floresiensis. Nature 441:624-628.

Happy quote of the day!

Ale, this one's for you! Overheard last night at the Festival International de Jazz de Montréal:

"Bonjour les amis. La musique brésilienne c'est pour les vacances, oublier les patrons, et faire des bisous sur la bouche."
- Seu Jorge.

This year's Festival has been outstanding, and between this and the World Cup (FORZA AZZURRI!!!!), it's so nice to be here! It provides undeniable motivation to get done with work by the early afternoon in any case! Next up in the line of great shows here is Calexico with Los Mariachis Luz de Luna in a few nights, and Wilco the night after that! Ah, l'été à Montréal!

Human responses to prehistoric volcanism: A review of reality

John Grattan of the University of Wales has a paper in a recent issue of Quaternary International on the impacts of volcanic eruptions on past societies, prehistoric and historic alike. It's a really level-headed discussion of the inferences that can actually be made about just how un-catastrophic most of these events are likely to have been. Of course, he doesn't deny the dramatic influence volcanic eruptions have had on certain past societies, especially in the immediate vicinity of the volcano. But he does emphasize how the impact of such events was, in all cases, mediated by the socio-economic, political and/or ecological context of the groups affected by volcanism, no matter how dramatic.

Equally important, in my opinion, is his demonstration that the supposedly 'tell-tale' repercussions of volcanic eruptions on human socioecosystems (e.g., famines, unusually harsh weather plague and pestilence, crop failure) have been documented historically even in periods during which there was no recorded "eruptions of note." In 9th Century Europe, such calamitous events appear to have occurred at an average frequency of fully one every three years, without there being any need to invoke volcanism as a prime mover. Perhaps the most important point that Grattan makes in his paper is that, by and large, the human response to catastrophic events has always been one of adaptation rather than annihilation. In other words, people were not just passive witnesses to the furies of the earth, but - unsurprisingly - took matters into their own hands to escape destruction by natural forces, or at the very least enact social, economic or technological strategies to more easily bear their adverse consequences. That being the case, people invoking volcanism as a prime mover for biological, cultural and/or technological changes in the past need to be very careful in establishing credible cause-effect relationships in order to support their arguments. This is especially true for those periods of the past for which our understanding of the chronology can still be quite shaky, such as the Late Pleistocene (e.g., Ambrose 1998). Given that volcanic deposits are easily characterized chemically and can be dated much more precisely than many other kinds of prehistoric deposits, it is also imperative to provide empirical data to support the correlation of a volcanic tuff in archaeological context to a specific volcanic eruption. Impressions and 'general chronostratigraphic agreements' are not enough to support scenarios invoking eruptions as significant agents of prehistoric change. And subsequently, it is crucial to account for the innate adaptability of human groups rather than postulating widespread societal and demographic collapse.

Grattan's paper is part of a special issue of Quaternary International entitled “Dark nature: responses of humans and ecosystems to rapid environmental changes,” edited S.A.G. Leroy, H. Jousse and M. Cremaschi. It includes a number of interesting papers focused mainly on more recent periods, but it does a very good job of demonstrating how archaeology can provide important information on issues of climate change and human responses to them, which are increasingly relevant today and how the discipline is uniquely positioned to serve as a productive meeting ground or mediator between the historical and natural sciences (van der Leeuw and Redman 2002). Good stuff.

References:

Ambrose, S. H. 1998. Late Pleistocene human population bottlenecks, volcanic winter and differentiation of modern humans. Journal of Human Evolution 34:623-651.

Grattan, J. 2006. Aspects of Armageddon: an exploration of the role of volcanic eruptions in human hitsory and civilization. Quaternary International 151:10-18.

van der Leeuw, S. E., and C. L. Redman. 2002. Placing archaeology at the center of socio-natural studies. American Antiquity 67:597-605.