Barbarians at the gate

Kevin Lewis

November 19, 2017

Annual War Deaths in Small-Scale versus State Societies Scale with Population Size Rather than Violence
Dean Falk & Charles Hildebolt
Current Anthropology, forthcoming


In The Better Angels of Our Nature: Why Violence has Declined, psychologist Steven Pinker cites mean ratios of war (battle) deaths suffered annually per 100,000 individuals as evidence for concluding that people who live in states are less violent than those who live or lived in “hunting, gathering, and horticultural societies in which our species spent most of its evolutionary history.” Because such ratios are blind to actual population sizes, it remains to be seen whether the apparent decrease in contemporary violence is an artifact of scaling factors. Here scaling of war deaths is quantified relative to actual population sizes for 11 chimpanzee communities, 24 human nonstates, and 19 and 22 countries that fought in World War I and World War II, respectively. Mean annual battle deaths expressed as percentages of population sizes scale inversely with population sizes in chimpanzees and humans, indicating increased vulnerability rather than increased violence in smaller populations. However, the absolute number of mean annual war deaths increases exponentially (superlinearly) and nearly identically with population sizes across human groups but not chimpanzees. These findings suggest that people evolved to be more violent than chimpanzees and that humans from nonstates are neither more nor less violent than those from states.

Greater post-Neolithic wealth disparities in Eurasia than in North America and Mesoamerica
Timothy Kohler et al.
Nature, forthcoming


How wealth is distributed among households provides insight into the fundamental characters of societies and the opportunities they afford for social mobility. However, economic inequality has been hard to study in ancient societies for which we do not have written records, which adds to the challenge of placing current wealth disparities into a long-term perspective. Although various archaeological proxies for wealth, such as burial goods or exotic or expensive-to-manufacture goods in household assemblages, have been proposed, the first is not clearly connected with households, and the second is confounded by abandonment mode and other factors. As a result, numerous questions remain concerning the growth of wealth disparities, including their connection to the development of domesticated plants and animals and to increases in sociopolitical scale. Here we show that wealth disparities generally increased with the domestication of plants and animals and with increased sociopolitical scale, using Gini coefficients computed over the single consistent proxy of house-size distributions. However, unexpected differences in the responses of societies to these factors in North America and Mesoamerica, and in Eurasia, became evident after the end of the Neolithic period. We argue that the generally higher wealth disparities identified in post-Neolithic Eurasia were initially due to the greater availability of large mammals that could be domesticated, because they allowed more profitable agricultural extensification, and also eventually led to the development of a mounted warrior elite able to expand polities (political units that cohere via identity, ability to mobilize resources, or governance) to sizes that were not possible in North America and Mesoamerica before the arrival of Europeans. We anticipate that this analysis will stimulate other work to enlarge this sample to include societies in South America, Africa, South Asia and Oceania that were under-sampled or not included in this study.

Optimising human community sizes
Robin Dunbar & Richard Sosis
Evolution and Human Behavior, forthcoming


We examine community longevity as a function of group size in three historical, small scale agricultural samples. Community sizes of 50, 150 and 500 are disproportionately more common than other sizes; they also have greater longevity. These values mirror the natural layerings in hunter-gatherer societies and contemporary personal networks. In addition, a religious ideology seems to play an important role in allowing larger communities to maintain greater cohesion for longer than a strictly secular ideology does. The differences in optimal community size may reflect the demands of different ecologies, economies and social contexts, but, as yet, we have no explanation as to why these numbers seem to function socially so much more effectively than other values.

Fortifications and Democracy in the Ancient Greek World
Josiah Ober & Barry Weingast
Stanford Working Paper, October 2017


In the modern world, access-limiting fortification walls are not typically regarded as promoting democracy. But in Greek antiquity, increased investment in fortifications was correlated with the prevalence and stability of democracy. This paper sketches the background conditions of the Greek city-state ecology, analyzes a passage in Aristotle’s Politics, and assesses the choices of Hellenistic kings, Greek citizens, and urban elites, as modeled in a simple game. The paper explains how city walls promoted democracy and helps to explain several other puzzles: why Hellenistic kings taxed Greek cities at lower than expected rates; why elites in Greek cities supported democracy; and why elites were not more heavily taxed by democratic majorities. The relationship between walls, democracy, and taxes promoted continued economic growth into the late classical and Hellenistic period (4th-2nd centuries BCE), and ultimately contributed to the survival of Greek culture into the Roman era, and thus modernity. We conclude with a consideration of whether the walls-democracy relationship holds in modernity.

Trade, Merchants, and the Lost Cities of the Bronze Age
Gojko Barjamovic et al.
NBER Working Paper, November 2017


We analyze a large dataset of commercial records produced by Assyrian merchants in the 19th Century BCE. Using the information collected from these records, we estimate a structural gravity model of long-distance trade in the Bronze Age. We use our structural gravity model to locate lost ancient cities. In many instances, our structural estimates confirm the conjectures of historians who follow different methodologies. In some instances, our estimates confirm one conjecture against others. Confronting our structural estimates for ancient city sizes to modern data on population, income, and regional trade, we document persistent patterns in the distribution of city sizes across four millennia, even after controlling for time-invariant geographic attributes such as agricultural suitability. Finally, we offer evidence in support of the hypothesis that large cities tend to emerge at the intersections of natural transport routes, as dictated by topography.

Pre-Neolithic evidence for dog-assisted hunting strategies in Arabia
Maria Guagnin, Angela Perri & Michael Petraglia
Journal of Anthropological Archaeology, forthcoming


The function of prehistoric dogs in hunting is not readily visible in the archaeological record; interpretations are thus heavily reliant on ethnographic data and remain controversial. Here we document the earliest evidence for dogs on the Arabian Peninsula from rock art at the sites of Shuwaymis and Jubbah, in northwestern Saudi Arabia. Hunting scenes depicted in the rock art illustrate dog-assisted hunting strategies from the 7th and possibly the 8th millennium BC, predating the spread of pastoralism. Though the depicted dogs are reminiscent of the modern Canaan dog, it remains unclear if they were brought to the Arabian Peninsula from the Levant or represent an independent domestication of dogs from Arabian wolves. A substantial dataset of 147 hunting scenes shows dogs partaking in a range of hunting strategies based on the environment and topography of each site, perhaps minimizing subsistence risk via hunting intensification in areas with extreme seasonal fluctuations. Particularly notable is the inclusion of leashes on some dogs, the earliest known evidence in prehistory. The leashing of dogs not only shows a high level of control over hunting dogs before the onset of the Neolithic, but also that some dogs performed different hunting tasks than others.

Volcanic suppression of Nile summer flooding triggers revolt and constrains interstate conflict in ancient Egypt
Joseph Manning et al.
Nature Communications, October 2017


Volcanic eruptions provide tests of human and natural system sensitivity to abrupt shocks because their repeated occurrence allows the identification of systematic relationships in the presence of random variability. Here we show a suppression of Nile summer flooding via the radiative and dynamical impacts of explosive volcanism on the African monsoon, using climate model output, ice-core-based volcanic forcing data, Nilometer measurements, and ancient Egyptian writings. We then examine the response of Ptolemaic Egypt (305–30 BCE), one of the best-documented ancient superpowers, to volcanically induced Nile suppression. Eruptions are associated with revolt onset against elite rule, and the cessation of Ptolemaic state warfare with their great rival, the Seleukid Empire. Eruptions are also followed by socioeconomic stress with increased hereditary land sales, and the issuance of priestly decrees to reinforce elite authority. Ptolemaic vulnerability to volcanic eruptions offers a caution for all monsoon-dependent agricultural regions, presently including 70% of world population.

Estimating mobility using sparse data: Application to human genetic variation
Liisa Loog et al.
Proceedings of the National Academy of Sciences, 14 November 2017, Pages 12213–12218


Mobility is one of the most important processes shaping spatiotemporal patterns of variation in genetic, morphological, and cultural traits. However, current approaches for inferring past migration episodes in the fields of archaeology and population genetics lack either temporal resolution or formal quantification of the underlying mobility, are poorly suited to spatially and temporally sparsely sampled data, and permit only limited systematic comparison between different time periods or geographic regions. Here we present an estimator of past mobility that addresses these issues by explicitly linking trait differentiation in space and time. We demonstrate the efficacy of this estimator using spatiotemporally explicit simulations and apply it to a large set of ancient genomic data from Western Eurasia. We identify a sequence of changes in human mobility from the Late Pleistocene to the Iron Age. We find that mobility among European Holocene farmers was significantly higher than among European hunter–gatherers both pre- and postdating the Last Glacial Maximum. We also infer that this Holocene rise in mobility occurred in at least three distinct stages: the first centering on the well-known population expansion at the beginning of the Neolithic, and the second and third centering on the beginning of the Bronze Age and the late Iron Age, respectively. These findings suggest a strong link between technological change and human mobility in Holocene Western Eurasia and demonstrate the utility of this framework for exploring changes in mobility through space and time.

Parallel palaeogenomic transects reveal complex genetic history of early European farmers
Mark Lipson et al.
Nature, 16 November 2017, Pages 368–372


Ancient DNA studies have established that Neolithic European populations were descended from Anatolian migrants who received a limited amount of admixture from resident hunter-gatherers. Many open questions remain, however, about the spatial and temporal dynamics of population interactions and admixture during the Neolithic period. Here we investigate the population dynamics of Neolithization across Europe using a high-resolution genome-wide ancient DNA dataset with a total of 180 samples, of which 130 are newly reported here, from the Neolithic and Chalcolithic periods of Hungary (6000–2900 BC, n = 100), Germany (5500–3000 BC, n = 42) and Spain (5500–2200 BC, n = 38). We find that genetic diversity was shaped predominantly by local processes, with varied sources and proportions of hunter-gatherer ancestry among the three regions and through time. Admixture between groups with different ancestry profiles was pervasive and resulted in observable population transformation across almost all cultural transitions. Our results shed new light on the ways in which gene flow reshaped European populations throughout the Neolithic period and demonstrate the potential of time-series-based sampling and modelling approaches to elucidate multiple dimensions of historical population interactions.

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