Alternative Pathways to Complexity: Evolutionary Trajectories in the Middle Paleolithic and Middle Stone Age

ORGANIZER’S STATEMENT: Genetic findings suggest that Neanderthals and anatomically modern Homo sapiens last shared a common ancestor roughly 500,000 years ago. Although they may have remained genetically compatible, at the time of the most recent of the human dispersals out of Africa and into western Eurasia the two meta-populations had been partially if not wholly largely isolated from one another for at least 400,000 years. A certain amount of encephalization, and a great deal of cultural evolution, occurred between the time the two lineages separated and the time they came into interaction in the later Pleistocene. As a result of this long period of geographic vicariance, Neanderthals and African Homo sapiens represent a unique experiment in parallel biological and cultural evolution.

For the most part, assessments of the different behavioral evolutionary paths followed by hominins in Eurasia and Africa have concerned the relative evolutionary status of the Middle Paleolithic (MP) and Middle Stone Age (MSA). There has been particular emphasis on the expression of a shifting set of traits referred to as “modern human behavior.” Differences in behavioral tendencies among MP and MSA hominins may (or may not) help us explain the historical circumstances of the Neanderthal’s disappearance and the rapid dispersal and persistence of modern humans across the globe. However, attempts to establish the relative positions of the MP and MSA in a progressive developmental narrative culminating in “behavioral modernity” distract us from a unique and more valuable opportunity, namely to take advantage of the real life “experiment” created by the long separation of Neanderthal and anatomically modern H.s. lineages. Such differences as exist may help us describe distinct and partially independent evolutionary paths to very large brains, complex cognition, and flexible behavior.

The meeting’s organizers, Steven L. Kuhn and Erella Hovers, were interested in creating a forum for empirically-based, theoretically informed discussions of this evolutionary experiment, independent of the eventual success of one population or the other. The goal was not to formulate a consensus about which of the two populations first reached some threshold of “behavioral modernity”. This is an interesting but, in some ways, anecdotal question. Instead, the specific aims of the symposium were to discuss and evaluate the independent histories of evolution in behavior and cognition in western Eurasia and southern Africa. We wanted to highlight the important differences and similarities in the evolutionary trajectories in sub-Saharan Africa and western Eurasia, and to link them wherever possible with the environmental and demographic conditions in the two macro-regions. A more abstract goal was to discuss how the paleoanthropological record, with its unique perspective on long-term behavioral change, could provide an opportunity for our discipline to make a contribution to evolutionary research more generally.

With these questions in mind, the 145th symposium of the Wenner-Gren Foundation was convened at Häringe Slott near Stockholm, Sweden (befittingly, a former residence of the Foundation’s benefactor Axel Wenner-Gren) from June 1-8, 2012. The location and timing enabled participants to enjoy (or suffer) sun light for 20 hours a day, at least when the sun was visible. Invitees were asked to draw on evidence in their areas of expertise, focusing on evolutionary trends in both modal tendencies and levels of variation/diversity within various regions. As dictated by the nature of the questions asked, the 15 participants brought to the discussion table (and to the coffee and cookies table, the dinner table, and the cocktail table) a diversity of training and expertise. The group included paleoanthropologists who study material culture and subsistence in Eurasia, Africa and China, physical anthropologists, scientists interested in demography, modelers of cultural evolution, and a climatologist. One invitee, a geneticist, had to cancel at the last minute, and Leslie Aiello, president of the Wenner-Gren Foundation in New York, courageously stepped up and took on the role of representing his paper. The papers and discussions focused on the time period between 400 Ka and 40 Ka (MIS 9-3), the interval in which the MSA and MP developed, spread, and eventually disappeared. The student monitor for the meeting, Ariel Malinsky-Buller, currently writes his Ph.D. thesis on the transition from the late Lower to the early Middle Paleolithic in Eurasia.

That many of the papers presented in the formal session were co-authored by two or more scientists is perhaps a reflection of the scope and scale of the questions addressed. Paleoanthropologists Steve Kuhn and Christian Tryon led off the first session of formal presentations. Each provided overviews of respective regional records of Eurasia and Africa based on the empirical data, laying out the geographic and cultural canvases for the whole meeting and emphasizing main phenomena to be explained, as well as biases in the understanding of the regional records. Eelco Rohling completed this session with a comprehensive review of global environmental conditions and especially climate variability, as the backdrop to the period of interest, identifying periodic chances for dispersal opportunities and emphasizing the volatile nature of Upper Pleistocene climate in Africa and Europe. In the second session archaeozoologists Mary Stiner and Jamie Clark focused on the links between subsistence behavior, climate, and demographic conditions experienced by Eurasian and south African populations, while demographer modeler Anna Degioanni discussed diverse population estimates and environmental constraints on Neanderthal populations. A number of the participants in the first two sessions emphasized the apparent sparseness and fragility of MP populations, based on a wide variety of evidence. In the third session Sarah Würz, Ignacio de la Torre and Xing Gao discussed technological change and variability in South Africa, Iberia and China, respectively. The geographic scales of the presentations were different, yet on each one of these scales the speakers defined – somewhat unexpectedly – many levels and aspects of cultural continuity as well as very different temporal dynamics. In the fourth session Osbjorn Pearson discussed the effects of climate on demography, and how this could have influenced the evolutionary mechanisms that led to the distinct anatomies of Neandertals and modern humans. Leslie Aiello represented the paper by Carles Lalueza-Fox as a cautionary tale about the use of paleogenetic research, emphasizing that up to now, this research has expanded our understanding of the genetic history of modern humans but less so, of the ancient populations of non-modern hominins. Erella Hovers reviewed the Levantine record 300-50 thousand years ago, also identifying elements of continuity in material culture in a region where population movements are potentially best documented for the time frame involved. She used this record to bring up questions about the roles of climate, material culture function, and processes of cultural transmission within and between populations in the shaping of the evolutionary record of the late Middle and early part of the Upper Pleistocene. In the last formal session Charles Perreault, Francesco d’Errico and Mark Collard presented three different perspectives on explaining cultural evolutionary trajectories, focusing on cultural evolution theory, eco-niche modeling that identifies the environmental features shared by sites/assemblages attributed to specific techno-complexes or cultures, and on phylogenetic methods as a means of evaluating and refining the reconstruction of potential cultural evolutionary scenarios, points of coalescence and the identification of derived or analogous cultural traits.

After a day off in Stockholm, complete with the surprising appearance of the sun after a number of rainy days, a rousing performance of Swedish folk music back at the castle, and a birthday party in honor of Axel Wenner-Gren, the group re-assembled for two rather intensive days of discussion. Several overarching themes emerged from the presentations and the ensuing conversations. Not surprisingly there seemed to be a consensus that it is high time to improve upon simple, uni-causal and easy-to-model scenarios that have dominated the literature. Another conclusion was that current understanding of different rates of cultural evolution in Africa and Eurasia may be biased by great differences in geographic scales, the density of sites, and in the patterns of climate variability within and between these two continental records, as well as biases introduced by research practices and histories. From a bird’s-eye view the Eurasian record sometimes appears monotonous, but when broken down to regions it manifested technological diversity and variability. At the same time the group discussed practical ways to restructure regional and continental perspectives so as to produce greater comparability. There was discussion of temporal scale also in the context of harnessing the strengths of the archaeological record towards answering the fundamental question of the appearance of cumulative culture among hominins. To tackle this issue, it is necessary to use the inherent temporality of the record to our advantage rather than to ignore it.

When paleoanthropology turns to climate sciences to define the environmental envelope of MSA/MP behaviors in various regions, spatial and temporal scales are often incompatible. Climate variability in the Upper Pleistocene is often documented on a millennial, centennial or (rarely) decadal scale of resolution, yet dating of archaeological sites does not normally achieve such precision. On the other hand, sites are of restricted spatial scales whereas climatic events occur on a global basis. Features of the landscape play a major role in determining how these global events are manifest at the scale of sites or research areas. A great deal of discussion focused on strategies for resolving these geographic and temporal incongruities, ranging from development of local records to focusing on periods of high and low variability rather than specific sets of conditions.

It was clear from presentations and discussions that demography and its effects on cultural transmission have become fundamental to explanations of MP/MSA technological variation, foraging, and anatomy. The majority of participants subscribed to the view that Neandertals were as a rule spread thin on the ground, from which assumption many hypotheses about variation and innovation in cultural practices were derived. As compelling as demographic models may be, it is also clear that their implications have not been adequately explored for paleoanthropological time scales. There is an urgent need to design more specific and fine-tuned demographic models for Neandertals, to evaluate the viability of the hypothesized small groups in specific environmental conditions, and to investigate how their demographic re-organization on the landscape may have influenced cultural evolutionary processes. It is also important to provide actual tests of neutral models, and to pit them against models of adaptively-linked variation in behavior.

During discussions in the last day of the meeting, participants worked to construct models that can generate testable hypotheses about rates of innovation and change and their retention in the cultural record to a degree that may enable cumulative cultural evolution. Working groups proposed frameworks for evaluating complexity of technical processes and for comparing cultural assemblages across regions with very different histories. Because of its intensive study of terrestrial, small scale climatic variability, patchy environment, the specificity of its climate, its ‘checkered’ history in terms of hominin taxonomy and dispersal, and thanks to many highly detailed studies of lithic material culture, research on the Levantine MP may serve as a first approximation for constructing research programs that are suitable to address the specific questions raised in the meeting and a basis on which to incorporate new methods of analysis. Southern Africa, southwest Europe (northern Iberia, southern France) were also nominated as areas of roughly comparable size and data density.

In the end it became obvious that we are not yet in a position to fully evaluate and understand the outcomes of the parallel evolutionary experiments that led to anatomically modern Homo sapiens and the MSA in Africa, and to Neanderthals and the MP in Europe. Whereas the basic notion is sound, and some of the available evidence compelling, conventional approaches to reporting, synthesizing and comparing data do not lend themselves to rigorous tests of alternative evolutionary models. At the same time, the participants agreed that the intellectual tools needed to research these questions are well within reach. Various members of the group have begun collaborative efforts in this direction, including the design and implementation of pilot studies of cumulative evolution using material culture data, and attempts to identify phylogenetic relationships between MP and MSA cultural entities. These collaborative studies are underway as we write these words. This fulfills one of the aims of the workshop, which was to open up new avenues for collaboration among participants and their colleagues in a range of disciplines. Proceedings of the workshop, to be published as a special issue of Current Anthropology (with peer review), will reflect these new joint efforts.

Current Anthropology supplement on the UCP website

Wenner-Gren Symposium #145