Mesoamerican urbanism revisited: Environmental change, adaptation, resilience, persistence, and collapse.

Urban adaptation to climate change is a global challenge requiring a broad response that can be informed by how urban societies in the past responded to environmental shocks. Yet, interdisciplinary efforts to leverage insights from the urban past have been stymied by disciplinary silos and entrenched misconceptions regarding the nature and diversity of premodern human settlements and institutions, especially in the case of prehispanic Mesoamerica. Long recognized as a distinct cultural region, prehispanic Mesoamerica was the setting for one of the world's original urbanization episodes despite the impediments to communication and resource extraction due to the lack of beasts of burden and wheeled transport, and the limited and relatively late use of metal implements. Our knowledge of prehispanic urbanism in Mesoamerica has been significantly enhanced over the past two decades due to significant advances in excavating, analyzing, and contextualizing archaeological materials. We now understand that Mesoamerican urbanism was as much a story about resilience and adaptation to environmental change as it was about collapse. Here we call for a dialogue among Mesoamerican urban archaeologists, sustainability scientists, and researchers interested in urban adaptation to climate change through a synthetic perspective on the organizational diversity of urbanism. Such a dialogue, seeking insights into what facilitates and hinders urban adaptation to environmental change, can be animated by shifting the long-held emphasis on failure and collapse to a more empirically grounded account of resilience and the factors that fostered adaptation and sustainability.

Corrigendum: Greater post-Neolithic wealth disparities in Eurasia than in North America and Mesoamerica.

This corrects the article DOI: 10.1038/nature24646.

Greater post-Neolithic wealth disparities in Eurasia than in North America and Mesoamerica.

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.

Quantitative historical analysis uncovers a single dimension of complexity that structures global variation in human social organization.

Do human societies from around the world exhibit similarities in the way that they are structured, and show commonalities in the ways that they have evolved? These are long-standing questions that have proven difficult to answer. To test between competing hypotheses, we constructed a massive repository of historical and archaeological information known as "Seshat: Global History Databank." We systematically coded data on 414 societies from 30 regions around the world spanning the last 10,000 years. We were able to capture information on 51 variables reflecting nine characteristics of human societies, such as social scale, economy, features of governance, and information systems. Our analyses revealed that these different characteristics show strong relationships with each other and that a single principal component captures around three-quarters of the observed variation. Furthermore, we found that different characteristics of social complexity are highly predictable across different world regions. These results suggest that key aspects of social organization are functionally related and do indeed coevolve in predictable ways. Our findings highlight the power of the sciences and humanities working together to rigorously test hypotheses about general rules that may have shaped human history.

Imperial expansion, public investment, and the long path of history: China's initial political unification and its aftermath.

The Neolithic (ca. 8000-1900 B.C.) underpinnings of early Chinese civilization had diverse geographic and cultural foundations in distinct traditions, ways of life, subsistence regimes, and modes of leadership. The subsequent Bronze Age (ca. 1900-221 B.C.) was characterized by increasing political consolidation, expansion, and heightened interaction, culminating in an era of a smaller number of warring states. During the third century B.C., the Qin Dynasty first politically unified this fractious landscape, across an area that covers much of what is now China, and rapidly instituted a series of infrastructural investments and other unifying measures, many of which were maintained and amplified during the subsequent Han Dynasty. Here, we examine this historical sequence at both the national and macroscale and more deeply for a small region on the coast of the Shandong Province, where we have conducted several decades of archaeological research. At both scales, we examine apparent shifts in the governance of local diversity and some of the implications both during Qin-Han times and for the longer durée.

Cooperation, collective action, and the archeology of large-scale societies.

Archeologists investigating the emergence of large-scale societies in the past have renewed interest in examining the dynamics of cooperation as a means of understanding societal change and organizational variability within human groups over time. Unlike earlier approaches to these issues, which used models designated voluntaristic or managerial, contemporary research articulates more explicitly with frameworks for cooperation and collective action used in other fields, thereby facilitating empirical testing through better definition of the costs, benefits, and social mechanisms associated with success or failure in coordinated group action. Current scholarship is nevertheless bifurcated along lines of epistemology and scale, which is understandable but problematic for forging a broader, more transdisciplinary field of cooperation studies. Here, we point to some areas of potential overlap by reviewing archeological research that places the dynamics of social cooperation and competition in the foreground of the emergence of large-scale societies, which we define as those having larger populations, greater concentrations of political power, and higher degrees of social inequality. We focus on key issues involving the communal-resource management of subsistence and other economic goods, as well as the revenue flows that undergird political institutions. Drawing on archeological cases from across the globe, with greater detail from our area of expertise in Mesoamerica, we offer suggestions for strengthening analytical methods and generating more transdisciplinary research programs that address human societies across scalar and temporal spectra.

Archaeology as a social science.

Because of advances in methods and theory, archaeology now addresses issues central to debates in the social sciences in a far more sophisticated manner than ever before. Coupled with methodological innovations, multiscalar archaeological studies around the world have produced a wealth of new data that provide a unique perspective on long-term changes in human societies, as they document variation in human behavior and institutions before the modern era. We illustrate these points with three examples: changes in human settlements, the roles of markets and states in deep history, and changes in standards of living. Alternative pathways toward complexity suggest how common processes may operate under contrasting ecologies, populations, and economic integration.

The imprint of China's first emperor on the distant realm of eastern Shandong.

Imperial expansion is recurrent in human history. For early empires, such as in ancient China, this process generally is known from texts that glorify and present the perspective of vectors. The legacy of the Qin king, Shihuangdi, who first unified China in 221 BC, remains vital, but we have few details about the consequences of his distant conquests or how they changed the path of local histories. We integrate documentary accounts with the findings of a systematic regional survey of archaeological sites to provide a holistic context for this imperialistic episode and the changes that followed in coastal Shandong.

Navigating polycrisis: long-run socio-cultural factors shape response to changing climate.

Climate variability and natural hazards like floods and earthquakes can act as environmental shocks or socioecological stressors leading to instability and suffering throughout human history. Yet, societies experience a wide range of outcomes when facing such challenges: some suffer from social unrest, civil violence or complete collapse; others prove more resilient and maintain key social functions. We currently lack a clear, generally agreed-upon conceptual framework and evidentiary base to explore what causes these divergent outcomes. Here, we discuss efforts to develop such a framework through the Crisis Database (CrisisDB) programme. We illustrate that the impact of environmental stressors is mediated through extant cultural, political and economic structures that evolve over extended timescales (decades to centuries). These structures can generate high resilience to major shocks, facilitate positive adaptation, or, alternatively, undermine collective action and lead to unrest, violence and even societal collapse. By exposing the ways that different societies have reacted to crises over their lifetime, this framework can help identify the factors and complex social-ecological interactions that either bolster or undermine resilience to contemporary climate shocks. This article is part of the theme issue 'Climate change adaptation needs a science of culture'.

Disentangling the evolutionary drivers of social complexity: A comprehensive test of hypotheses.

During the Holocene, the scale and complexity of human societies increased markedly. Generations of scholars have proposed different theories explaining this expansion, which range from broadly functionalist explanations, focusing on the provision of public goods, to conflict theories, emphasizing the role of class struggle or warfare. To quantitatively test these theories, we develop a general dynamical model based on the theoretical framework of cultural macroevolution. Using this model and Seshat: Global History Databank, we test 17 potential predictor variables proxying mechanisms suggested by major theories of sociopolitical complexity (and >100,000 combinations of these predictors). The best-supported model indicates a strong causal role played by a combination of increasing agricultural productivity and invention/adoption of military technologies (most notably, iron weapons and cavalry in the first millennium BCE).

Assessing Classic Maya multi-scalar household inequality in southern Belize.

Inequality is present to varying degrees in all human societies, pre-modern and contemporary. For archaeological contexts, variation in house size reflects differences in labor investments and serves as a robust means to assess wealth across populations small and large. The Gini coefficient, which measures the degree of concentration in the distribution of units within a population, has been employed as a standardized metric to evaluate the extent of inequality. Here, we employ Gini coefficients to assess wealth inequality at four nested socio-spatial scales-the micro-region, the polity, the district, and the neighborhood-at two medium size, peripheral Classic Maya polities located in southern Belize. We then compare our findings to Gini coefficients for other Classic Maya polities in the Maya heartland and to contemporaneous polities across Mesoamerica. We see the patterning of wealth inequality across the polities as a consequence of variable access to networks of exchange. Different forms of governance played a role in the degree of wealth inequality in Mesoamerica. More autocratic Classic Maya polities, where principals exercised degrees of control over exclusionary exchange networks, maintained high degrees of wealth inequality compared to most other Mesoamerican states, which generally are characterized by more collective forms of governance. We examine how household wealth inequality was reproduced at peripheral Classic Maya polities, and illustrate that economic inequity trickled down to local socio-spatial units in this prehispanic context.

Rise of the war machines: Charting the evolution of military technologies from the Neolithic to the Industrial Revolution.

What have been the causes and consequences of technological evolution in world history? In particular, what propels innovation and diffusion of military technologies, details of which are comparatively well preserved and which are often seen as drivers of broad socio-cultural processes? Here we analyze the evolution of key military technologies in a sample of pre-industrial societies world-wide covering almost 10,000 years of history using Seshat: Global History Databank. We empirically test previously speculative theories that proposed world population size, connectivity between geographical areas of innovation and adoption, and critical enabling technological advances, such as iron metallurgy and horse riding, as central drivers of military technological evolution. We find that all of these factors are strong predictors of change in military technology, whereas state-level factors such as polity population, territorial size, or governance sophistication play no major role. We discuss how our approach can be extended to explore technological change more generally, and how our results carry important ramifications for understanding major drivers of evolution of social complexity.

Archaeological assessment reveals Earth's early transformation through land use.

Environmentally transformative human use of land accelerated with the emergence of agriculture, but the extent, trajectory, and implications of these early changes are not well understood. An empirical global assessment of land use from 10,000 years before the present (yr B.P.) to 1850 CE reveals a planet largely transformed by hunter-gatherers, farmers, and pastoralists by 3000 years ago, considerably earlier than the dates in the land-use reconstructions commonly used by Earth scientists. Synthesis of knowledge contributed by more than 250 archaeologists highlighted gaps in archaeological expertise and data quality, which peaked for 2000 yr B.P. and in traditionally studied and wealthier regions. Archaeological reconstruction of global land-use history illuminates the deep roots of Earth's transformation and challenges the emerging Anthropocene paradigm that large-scale anthropogenic global environmental change is mostly a recent phenomenon.

Implications of new petrographic analysis for the Olmec "mother culture" model.

Petrographic analysis of Formative Mexican ceramics by J. B. Stoltman et al. (see the companion piece in this issue of PNAS) refutes a recent model of Olmec "one-way" trade. In this paper, we address the model's more fundamental problems of sampling bias, anthropological implausibility, and logical non sequiturs. No bridging argument exists to link motifs on pottery to the social, political, and religious institutions of the Olmec. In addition, the model of unreciprocated exchange is implausible, given everything that the anthropological and ethnohistoric records tell us about non-Western societies of that general sociopolitical level.