Stephen Shennan

Late Pleistocene Demography and the Appearance of Modern Human Behavior

War and Peace? Modern behavior, including the development of advanced tools, musical instruments, and art, seems to have arisen in humans in stages. The earliest hints are seen in Africa about 70 to 90,000 years ago, but later in Europe about 45,000 years ago. An ongoing discussion centers on the origins and significance of human prosociality. During early human development, could the benefits of altruistic behavior have outweighed its costs (see the Perspective by Mace)? Bowles (p. 1293) constructed a model of conflict between groups of humans and extracted estimates of the critical parameters from archaeological and ethnographic data sets. Provocatively, it appears that warfare might have enhanced the emergence and persistence of altruistic behavior. Powell et al. (p. 1298) present a population model that shows that the development of modern behaviors may rely on the attainment of critical population densities and migratory patterns required for stable cultural transmission. The model is consistent with genetic inferences of population dynamics in Africa and Europe and suggests that these cultural changes may not solely reflect increased cognitive evolution. Population size and migration account for modern human behavior appearing in Africa about 90,000 years ago but much later across Europe. The origins of modern human behavior are marked by increased symbolic and technological complexity in the archaeological record. In western Eurasia this transition, the Upper Paleolithic, occurred about 45,000 years ago, but many of its features appear transiently in southern Africa about 45,000 years earlier. We show that demography is a major determinant in the maintenance of cultural complexity and that variation in regional subpopulation density and/or migratory activity results in spatial structuring of cultural skill accumulation. Genetic estimates of regional population size over time show that densities in early Upper Paleolithic Europe were similar to those in sub-Saharan Africa when modern behavior first appeared. Demographic factors can thus explain geographic variation in the timing of the first appearance of modern behavior without invoking increased cognitive capacity.

Demography and cultural innovation: A model and its implications for the emergence of modern human culture

In recent years there has been a major growth of interest in exploring the analogies between the genetic transmission of information from one generation to the next and the processes of cultural transmission, in an attempt to obtain a greater understanding of how culture change occurs. This article uses computer simulation to explore the implications of a specific model of the relationship between demography and innovation within an evolutionary framework. The consequences of innovation appear far more successful in larger populations than in smaller ones. In conclusion, it is suggested that the model has major implications for the origins of modern human culture in the last 50,000 years, which may be seen not as the result of genetic mutations leading to improved cognitive capacities of individuals, but as a population consequence of the demographic growth and increased contact range which are evident at this time. It is also proposed that the model may be of general relevance for understanding the process of cultural evolution in modern and pre-modern humans.

Random drift and culture change

We show that the frequency distributions of cultural variants, in three different real–world examples—first names, archaeological pottery and applications for technology patents—follow power laws that can be explained by a simple model of random drift. We conclude that cultural and economic choices often reflect a decision process that is value–neutral; this result has far–reaching testable implications for social–science research.

Regional population collapse followed initial agriculture booms in mid-Holocene Europe

Following its initial arrival in SE Europe 8,500 years ago agriculture spread throughout the continent, changing food production and consumption patterns and increasing population densities. Here we show that, in contrast to the steady population growth usually assumed, the introduction of agriculture into Europe was followed by a boom-and-bust pattern in the density of regional populations. We demonstrate that summed calibrated radiocarbon date distributions and simulation can be used to test the significance of these demographic booms and busts in the context of uncertainty in the radiocarbon date calibration curve and archaeological sampling. We report these results for Central and Northwest Europe between 8,000 and 4,000 cal. BP and investigate the relationship between these patterns and climate. However, we find no evidence to support a relationship. Our results thus suggest that the demographic patterns may have arisen from endogenous causes, although this remains speculative.

Population, culture history, and the dynamics of culture change

If archaeology is to succeed in explaining culture change, it must view the archaeological record from the perspective of cultural “descent with modification,” in so doing returning to many of the issues addressed by the culture‐history agenda rejected 30–40 years ago. This involves a consideration of the processes affecting cultural transmission. Many of these are strongly affected by the history of the biological populations in which cultural transmission occurs. It can be shown that prehistoric populations fluctuated much more than used to be thought and that these fluctuations can be hard to detect archaeologically. They can often be associated with cultural changes, and, in fact, the size of populations affects the nature of cultural processes in a variety of ways. These general points are illustrated with reference to a case study from the circum‐Alpine Neolithic, where dendrochronology provides high‐resolution dating.

Neolithic transition in Europe: the radiocarbon record revisited

Understanding the introduction of farming and the adoption of Neolithic culture continues to be a major research objective in Europe. The authors make use of a new database of radiocarbon dates from Mesolithic and Neolithic sites to map the transition. While the overall effect is still a diffusion into Europe from the south-east, detailed spatial analysis reveals fascinating local variations: in some places change was rapid, and one population replaced another, in others it was gradual and owed to incoming ideas rather than people.

Archaeobotanical evidence for the spread of farming in the eastern Mediterranean

A major topic of debate in Old World prehistory is the relative importance of population movement versus cultural diffusion in explaining the spread of agriculture into and across Europe following its inception in southwestern Asia. An important set of data that has surprisingly been largely absent from this debate is the preserved crops and associated weeds of the earliest farmers. An analysis of archaeobotanical data from 40 aceramic Neolithic sites in southwestern Asia and southeastern Europe shows that there are vegetational signatures that characterize the different geographical regions occupied by the Early Neolithic farmers. On this basis it is argued that the compositional similarities of the crop package between the Levantine core, Cyprus, and Greece are indicative of both the routes of migration of early farming groups and the early agricultural practices of Europes first farmers.

The Development of Social Stratification in Bronze Age Europe [and Comments and Reply]

The emergence of a hereditary elite class in Bronze Age Europe is now widely interpreted in terms of the redistributive activities of a managerial ruling class. This fuctionalist account of elite origins goes against a uniformitarian understanding of what ruling classes do in complex societies. It also is poorly suited to the concrete evidence for Bronze Age cultures in Europe. The rise of hereditary, superordinate social strata in prehistoric Europe is better understood as a consequence of the development of capital-intensive subsistence techniques. Plow agriculture, Mediterranean polyculture, irrigation, and offshore fishing limited the possibility of group fission and thereby gave leaders the opportunity to exploit basic producers over the long term. The observations that capital-intensification preceded elite emergence and that areas with greater intensification exhibited greater social inequalities confirm this nonfuctionalist account of the development of stratification in later prehistoric Europe.

Cultural transmission and stochastic network growth

Archaeological theory has traditionally presupposed the existence of “battleship curves” in stylistic evolution, with little understanding about what governs the width (variant frequency) or length (variant lifespan) of these curves. In terms of these variables, we propose that there is a testable difference between independent decisions, unbiased transmission, and biased transmission in cultural evolution. We expect independent decision making to be represented by an exponential distribution of variant prevalence in the population. In contrast, unbiased transmission tends to be characterized by a power law or log-normal distribution of prevalence, while biased transmission should deviate significantly from the unbiased case. The difference between these categories may be fundamental to how cultural traits spread and persist. In order to make analytical predictions for unbiased transmission, we adapt a model of stochastic network growth that, by quantitatively demonstrating the inherent nonlinearity in unbiased transmission, can explain why a few highly popular styles can be expected to emerge in the course of cultural evolution. For the most part, this model predicts the frequencies of pottery decorations remarkably well over a 400-year span of Linearbandkeramik settlement in the Merzbach valley. Because the highest frequencies of actual motifs are somewhat less than predicted by our unbiased transmission model, we identify an anti-conformist, or pro-novelty, bias in the later phases of the Neolithic Merzbach Valley.

Early farmers from across Europe directly descended from Neolithic Aegeans

Significance One of the most enduring and widely debated questions in prehistoric archaeology concerns the origins of Europe’s earliest farmers: Were they the descendants of local hunter-gatherers, or did they migrate from southwestern Asia, where farming began? We recover genome-wide DNA sequences from early farmers on both the European and Asian sides of the Aegean to reveal an unbroken chain of ancestry leading from central and southwestern Europe back to Greece and northwestern Anatolia. Our study provides the coup de grâce to the notion that farming spread into and across Europe via the dissemination of ideas but without, or with only a limited, migration of people. Farming and sedentism first appeared in southwestern Asia during the early Holocene and later spread to neighboring regions, including Europe, along multiple dispersal routes. Conspicuous uncertainties remain about the relative roles of migration, cultural diffusion, and admixture with local foragers in the early Neolithization of Europe. Here we present paleogenomic data for five Neolithic individuals from northern Greece and northwestern Turkey spanning the time and region of the earliest spread of farming into Europe. We use a novel approach to recalibrate raw reads and call genotypes from ancient DNA and observe striking genetic similarity both among Aegean early farmers and with those from across Europe. Our study demonstrates a direct genetic link between Mediterranean and Central European early farmers and those of Greece and Anatolia, extending the European Neolithic migratory chain all the way back to southwestern Asia.