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Data, Materials, and Software Availability: All study data are included in the article and/or supporting information available online at https://www.pnas.org/lookup/doi/10.1073/pnas.2220124120#supplementary-materials . Copyright © 2023 the Author(s). To address claims of human exceptionalism, we determine where humans fit within the greater mammalian distribution of reproductive inequality. We show that humans exhibit lower reproductive skew (i.e., inequality in the number of surviving offspring) among males and smaller sex differences in reproductive skew than most other mammals, while nevertheless falling within the mammalian range. Additionally, female reproductive skew is higher in polygynous human populations than in polygynous nonhumans mammals on average. This patterning of skew can be attributed in part to the prevalence of monogamy in humans compared to the predominance of polygyny in nonhuman mammals, to the limited degree of polygyny in the human societies that practice it, and to the importance of unequally held rival resources to women’s fitness. The muted reproductive inequality observed in humans appears to be linked to several unusual characteristics of our species—including high levels of cooperation among males, high dependence on unequally held rival resources, complementarities between maternal and paternal investment, as well as social and legal institutions that enforce monogamous norms. This work was conducted as a part of the “Emergence of Hierarchy and Leadership in Mammalian Societies” group at the National Institute for Mathematical and Biological Synthesis, supported by NSF Award DBI-1300426 and the University of Tennessee, Knoxville. It was supported by NSF awards SMA-1329089 and SMA-1743019, and the Santa Fe Institute, as well as the Max Planck Institute for Evolutionary Anthropology, Department of Human Behavior, Ecology and Culture. S.G. was supported by the US Army Research Office grants W911NF-14-1-0637, W911NF-17-1-0150, and the Office of Naval Research grant W911NF-18-1-0138. Additional funding for data collection was provided by the Wenner-Gren Foundation for Anthropological Research awards: 8913 and 7970, by NSF awards: BCS-0924630, BCS-0925910, BCS-0848360, BCS-0514559, BCS-0613226, BCS-0827277, SES-9870429, and DDRIG-1357209, by the National Geographic Society awards: HJ-099R-17, 20113909, 8671-09, and 7968-06, by the Kone Foundation awards: 086809, 088423, and 088423, and by the Jacobs Foundation, the UCSB Broom Center for Demography, and the UCSB Department of Anthropology.

We report functional relationships between humans and canines based on observations in the village of Santa Cruz (Toledo District, Belize), emphasizing the cultural ecology of dogs in this lowland tropical rainforest setting and milpa agriculture subsistence system. Dogs pursue animals threatening field crops; they deter forest herbivores by leaving their scent along the myriad trails from the village to the milpa field plots; and they guard the homestead and foods stored there. Dogs also aid in daytime hunts for species that can be cornered. They are less useful in pursuits of fast species like deer and are protected from pursuing especially dangerous species like anteater or warri. Litter survival rates are low, and the lifespan of hunting dogs is significantly shorter than that of guard dogs due to hazards of forest pursuit. Explicit training for hunting is limited and maintenance costs are low as dogs are fed a partial ration of tortillas and otherwise scavenge for their diet. The village population of dogs appears not to be under genetic selection for hunting skills. Our results advance the comparative ethnographic study of this important domesticate; they should aid in the formulation and assessment of hypotheses about dog domestication and co-evolution with human society.

Explaining variation in hunter-gatherer livelihoods hinges on our ability to predict the tradeoffs and opportunities of pursuing different kinds of prey. Central to this problem is the commonly held assumption that larger animals provide higher returns upon encounter than smaller ones. However, to test this assumption, actualistic observations of hunting payoffs must be comparable across different social, technological, and ecological contexts. In this meta-analysis, we revisit published and unpublished estimates of prey return rates (n = 217 from 181 prey types) to assess, first, whether they are methodologically comparable, and second, whether they correlate with body size. We find systematic inter-study differences in how carcass yield, energetic content, and foraging returns are calculated. We correct for these inconsistencies first by calculating new estimates of energetic yield (kcals per kg live weight) and processing costs for over 300 species of terrestrial and avian game. We then recalculate on-encounter returns using a standardized formula. We find that body size is a poor predictor of on-encounter return rate, while prey characteristics and behavior, mode of procurement, and hunting technology are better predictors. Although prey body size correlates well with processing costs and edibility, relationships with pursuit time and energetic value per kilogram are relatively weak.

Cesario et al. argue that benchmarking the relative counts of killings by police on relative crime rates, rather than relative population sizes, generates a measure of racial disparity in the use of lethal force that is unbiased by differential crime rates. Their publication, however, lacked any formal derivation showing that their benchmarking methodology has the statistical properties required to establish such a claim. We use the causal model of lethal force by police conditional on relative crime rates implicit in their analyses and prove that their benchmarking methodology does not, in general, remove the bias introduced by crime rate differences. Instead, it creates strong statistical biases that mask true racial disparities, especially in the killing of unarmed noncriminals by police. Reanalysis of their data using formally derived criminality-correcting benchmarks shows that there is strong and statistically reliable evidence of anti-Black racial disparities in the killing of unarmed Americans by police in 2015–2016.

AIM: As a response of pastoralists to climate change, nomadic migration deeply shaped Chinese history during the imperial era. Existing research on climate‐driven nomadic migration is conducted mainly on a national–continental scale. To advance the current work, we aim to resolve migratory movements at a provincial–regional scale using a large and long‐term historical dataset as a first attempt. The spatio‐temporal features of nomadic migration under climatic effects, specifically precipitation, are analysed in the theoretical context of behavioural ecology. LOCATION: China. TIME: Imperial era (220 BC–1910 AD). STUDY SUBJECT: Nomadic pastoralist minorities in imperial China. METHODS: We frame the analysis using an ideal free distribution model. A total of 1,842 historical location records of pastoralist immigration are empirically examined. Precipitation anomalies and nomadic migration are statistically assessed with nonparametric and Poisson regression methods, and temporal interdependencies among provincial–regional migratory movements are explored with a vector autoregressive model. RESULTS: We divide imperial China into six regions according to statistical results and geographic factors. Overall, decreased precipitation and drought provoked pastoralist migrations in a north‐to‐south direction. Northern nomads, with an apparent preference for central China as a major destination, triggered the most conflicts with resident agriculturalists. Nomads originating from the Tibetan minority regions moved north‐eastward into Qinghai Province as their main destination. MAIN CONCLUSIONS: Long‐term regional patterns of pastoralist migration are closely associated with drought‐induced ecological change in imperial China. Climate‐driven dynamics assessed with long‐term historical data facilitate the understanding of climate–ecology–society interactions in behavioural ecology and macroecology. Moreover, findings from imperial China may imply that cultural acceptance and communications could avoid conflicts between immigrants and original residents when facing mass migration, an issue of growing contemporary urgency in many parts of the world.

Author(s): Winterhalder, Bruce P.; Puleston, Cedric O. | Abstract: We adopt an imagined exchequer, the functionary responsible in an early polity for securing resources from its agrarian subjects, and we develop a feature-rich demographic and environmental model to explore the population ecology of agricultural production in the context of population growth, Malthusian constraints and economic exploitation. The model system allows us to (i) identify and characterize a peak of surplus production early in population growth, prior to density-dependent constraints and (ii) characterize the taxation potential of a population at its Malthusian equilibrium. For a fixed total level of taxation the exchequer has two options: a small population taxed at a high rate, unstable to small perturbations, or a larger population taxed at a lower rate, which is stable. In a small and growing population it is more effective to tax goods; as the population approaches its density-dependent equilibrium it becomes more effective to tax labor. We likewise show that early agrarian states afflicted by stochastic variation in agronomic output face an extinction risk dependent on the level of taxation and magnitude of yield variation. Successful agrarian states balanced resource exploitation against dynamic population ecology constraints; we propose that fiscal mismanagement should be among the hypotheses for polity failure.

Hunters exhibit high skill across the life span, individuals vary substantially in skill, and age-related peaks vary across sites., Human adaptation depends on the integration of slow life history, complex production skills, and extensive sociality. Refining and testing models of the evolution of human life history and cultural learning benefit from increasingly accurate measurement of knowledge, skills, and rates of production with age. We pursue this goal by inferring hunters’ increases and declines of skill from approximately 23,000 hunting records generated by more than 1800 individuals at 40 locations. The data reveal an average age of peak productivity between 30 and 35 years of age, although high skill is maintained throughout much of adulthood. In addition, there is substantial variation both among individuals and sites. Within study sites, variation among individuals depends more on heterogeneity in rates of decline than in rates of increase. This analysis sharpens questions about the coevolution of human life history and cultural adaptation.

© 2018 The Authors A theoretical and applied literature has suggested that foragers search using Lévy flights, since Lévy flights can maximize the efficiency of search in the absence of information on the location of randomly distributed prey. Foragers, however, often have available to them at least some information about the distribution of prey, gained either through evolved mechanisms, experience and memory, or social transmission of information. As such, we might expect selection for heuristics that make use of such information to further improve the efficiency of random search. Here we present a general model of random search behavior that includes as special cases: area-restricted search, correlated random walks, Brownian search, and Lévy flights. This generative model allows foragers to adjust search parameters based on encounter-conditional and other heuristics. Using a simulation model, we demonstrate the efficiency gains of these search heuristics, and illustrate the resulting differences in the distributions of step-size and heading angle change they imply, relative to Lévy flights. We conclude by presenting a statistical model that can be fit to empirical data and a set of testable, quantitative predictions that contrast our model of adaptive search with the Lévy flight foraging hypothesis.

Tl\X/ENTY An Ecological Model for the Emergence of Institutionalized Social Hierarchies qon California’s Northern Channel Islands Douglas]. Kennett, Bruce Winterhaldergjacob Bartruflf - and_/on A/I. Erlandson 0 N E O F T H E central questions in anthro- pological archaeology is how and why insti- tutionalized social hierarchies evident in ranked societies and chiefdoms developed indepen- dently i.n multiple locations around the world during the Holocene (Feinman and Manzanjlla zooo; Flannery I998)._ Status competition and social inequality exist in all human groups, re- gardless of size or mode of production (Fried I967; Boehm zooo; Diehl 2.000). However, ar- chaeological evidence for significant and institu- tionalized intragroup differences in status and wealth are confined to the last I3,ooo years, well after the first evidence for anatomically modern humans in Afiica (ca. 150,000 years ago) and their subsequent appearance throughout much of the Old and New Worlds (Klein 2.004). The preponderance of archaeological evidence sug- gests that for the majority of human history groups remained small, occupied relatively large territories at low. densities, and moved periodi- cally to adapt to spatial and temporal fluctuations ir1 resources. The record also indicates that group fissioning, environmental infilling, and emigra- tion to diverse habitats were generally favored over localized increases in group size and density or other forms of intensification. Under these conditions, institutionalized hereditary leader- ship and significant differences in status and wealth rarely emerged or persisted. Archaeological evidence for ranked societies is often found in conjunction with clear indications of localized population aggregation, economic intensification, and territorial circumscription (Blake and Clark 1999; Cameiro 1970; Clark and Blalce I994; Hayden I98I). In some instances, ranking follows heightened commitrnent to agri- culture (Price and Gebauer 1995), but similar de- velopments occurred among hunter-gatherers in areas where wild resources are concentrated, such as in marine and other aquatic habitats (Erlandson 2.001; Kennett 2oo5; Palsson I988; Yesner 1980). ‘In these contexts, certain group members were able to acquire greater wealth and status by (I) manipulating economic, social, and political relationships to their own benefit (Earle 1987); (2.) controlling the flow'of exotic goods used to signal status (Flannery I972) ,' (3) monop- olizing the labor of other group members (Earle I987; Arnold 2.ooI); and (4) creating ideologies 397

Author(s): Kennett, DJ; Anderson, A; Winterhalder, B | Editor(s): Kennett, Douglas J; Winterhalder, Bruce | Abstract: Islands in Oceania were some of the last habitable land masses on earth to be colonized by humans. Current archaeological evidence suggests that these islands were colonized episodically rather than continuously, and that bursts of migration were followed by longer periods of sedentism and population growth. The decision to colonize isolated, unoccupied islands and archipelagos was complex and dependent on a variety of social, technological and environmental variables. In this chapter we develop an integrative, multivariate approach to island colonization in Oceania based on a model from behavioral ecology known as the Ideal Free Distribution. This ecological model provides a framework that considers the dynamic character of island suitability along with density-dependent and density-independent variables influencing migratory behavior. Unique among existing models, it can account for the episodic nature of certain aspects of the colonization process. Within this context we critically evaluate the role of foraging, lowlevel food production, and ultimately intensive food production, as important contextual variables that influenced decisions to disperse. We argue that intensive food production was one variable that contributed to decreasing suitability of island habitats, stimulating dispersal, and ultimately migrations to more distant islands in Oceania. © 2006 by The Regents of the University of California.

This study provides an ecological explanation for the distribution of Arctic Small Tool tradition (ASTt) settlements in Alaska and the origin of their arctic maritime adaptation. Theoretically grounded in the ideal free distribution (IFD) model, which predicts that higher ranked habitats will be occupied first and most continuously, we contend that the location of large mammals was a major factor influencing human dispersal and settlement decisions in the arctic and subarctic ecosystems of Alaska. We rank habitat suitability based on historic mammal population densities from wildlife ecology reports across predefined ecological zones in Alaska; we multiply densities by average animal weights per species to determine suitability rankings. Coastal habitats in Alaska are higher ranked than adjacent tundra habitats, but the interior boreal forest may have been the highest ranked, considering technological constraints of hunting aquatic species. The ASTt migration into Alaska created population pressure that promoted the colonization of the unoccupied Arctic coast and development of the dual, terrestrial-maritime economy. When pan-Alaska human populations declined around 3200–2500 years ago low ranked tundra ecoregions were abandoned. As human populations recovered Alaska coasts became the most densely populated habitats. The adaptive logic entailed in the IFD provides a consistent evolutionary interpretation for settlement patterns documented in this region.

Significance Using GPS trackers, we followed Nahua mushroom collectors to study how experienced foragers efficiently search for resources. Locating patchily distributed resources while reducing traveling costs requires a forager to balance time spent searching for new patches and searching within known patches. We present an analytical model of foraging behavior in which foragers can detect and change the way they search by adjusting direction and speed as a function of time since last resource encounter. This model can be used to test theoretical predictions concerning how long foragers should remain inside a given patch. Elucidating how organisms efficiently search is of widespread interest across academic disciplines: the potential applications of the method explained here range from conservation biology to robotic design., We develop a method of analysis for testing the marginal value theorem (MVT) in natural settings that does not require an independent definition or mapping of patches. We draw on recent theoretical work on area-restricted search (ARS) that links turning-angle and step-size changes to geographically localized encounter-rates. These models allow us to estimate “giving-up times” using encounter-annotated GPS tracking data. Applied to a case study of Nahua mushroom foragers, these models identify distinct forms of intrapatch and interpatch search behavior, with intrapatch search transitioning to interpatch search after a predictable interval of time since the last encounter with a harvested mushroom. Our empirical estimate of giving-up time coincides with the theoretically optimal giving-up time derived under the MVT in the same environment. The MVT is currently underused in studies of human foraging and settlement patterns, due in large part to the difficulty of identifying discrete resource patches and quantifying their characteristics. Our methods mitigate the need to make such discrete maps of patches and thus have the potential to broaden the scope for empirical evaluations of the MVT and related theory in humans. Beyond studies of naturalistic foraging in humans and other animals, our approach has implications for optimization of search behavior in a range of applied fields where search dynamics must be adapted to shifting patterns of environmental heterogeneity affecting prey density and patchiness.

© 2018 Springer Science+Business Media, LLC, part of Springer Nature While archaeologists now have demonstrated that barter and trade of material commodities began in prehistory, theoretical efforts to explain these findings are just beginning. We adapt the central place foraging model from behavioral ecology and the missing-market model from development economics to investigate conditions favoring the origins of household-level production for barter and trade in premodern economies. Interhousehold exchange is constrained by production, travel and transportation, and transaction costs; however, we predict that barter and trade become more likely as the number and effect of the following factors grow in importance: (1) local environmental heterogeneity differentiates households by production advantages; (2) preexisting social mechanisms minimize transaction costs; (3) commodities have low demand elasticity; (4) family size, gender role differentiation, or seasonal restrictions on household production lessen opportunity costs to participate in exchange; (5) travel and transportation costs are low; and (6) exchange opportunities entail commodities that also can function as money. Population density is not a direct cause of exchange but is implicated inasmuch as most of the factors we identify as causal at the household level become more salient as population density increases. We review archaeological, ethnohistoric, and ethnographic evidence for premodern marketing, observing that the model assumptions, variables, and predictions generally receive preliminary support. Overall, we argue that case study and comparative investigation of the origins of marketing will benefit from explicit modeling within the framework of evolutionary anthropology.

Archaeology’s broad engagement with the long-term evolution of human subsistence systems and social forms hinges on understanding relationships among environment, demography, production, and society. Semiquantitative narrative accounts of interactions among these factors by Malthus and later by Boserup currently are being updated with more explicitly quantitative analytical and simulation models. We describe one of these approaches, food-limited demography, and present examples of how it is being used to interpret archaeological data on subsistence, settlement, and the sociopolitical evolution of Pacific and North American societies. We note that dynamic modeling can reveal system properties that run counter to commonly held beliefs about population ecology. In agrarian societies the weight of Malthusian constraints on population develop not gradually, but abruptly, with severe consequences for human welfare; inter-annual food storage mitigates some instances of famine but makes others more severe; the potential for surplus production is greatest when populations are relatively small; low tax rates applied to a large population of producers are more stable than a high rate applied to a smaller population; and, at population equilibrium, a tax on labor may be more efficient than one on agrarian goods. These and other insights from contemporary modeling of linkages among human demography, behavior, economy, and environment allow us to examine the consequences of assumptions about rates of birth and death, the allocation of wealth and power, and how resources and labor are utilized in the evolution of early agricultural societies.

Active search for prey is energetically costly, so understanding how foragers optimize search has been central to foraging theory. Some theoretical work has suggested that foragers of randomly distributed prey should search using Lévy flights, while work on area-restricted and intermittent search strategies has demonstrated that foragers can use the information provided by prey encounters to more effectively adapt search direction and velocity. Previous empirical comparisons of these search modes have tended to rely on distribution-level analyses, due to the difficulty of collecting event-level data on encounters linked to the GPS tracks of foragers. Here we use a preliminary event-level data-set (18.7 hours of encounter-annotated focal follows over 6 trips) to show that two Colombian blowgun hunters use adaptive encounter-conditional heuristics, not non-conditional Lévy flights, when searching for prey. Using a theoretically derived Bayesian model, we estimate changes in turning-angle and search velocity as a function of encounters with prey at lagged time-steps, and find that: 1) hunters increase average turning-angle in response to encounters, producing a more tortuous search of patches of higher prey density, but adopt more efficient uni-directional, inter-patch movement after failing to encounter prey over a sufficient period of time; and, 2) hunters reduce search velocity in response to encounters, causing them to spend more of their search time in patches with demonstrably higher prey density. These results illustrate the importance of using event-level data to contrast encounter-conditional, area-restricted search and Lévy flights in explaining the search behavior of humans and other organisms.

Analyses of racial disparities in police use-of-force against unarmed individuals are central to public policy interventions; however, recent studies have come to apparently paradoxical findings concerning the existence and form of such disparities. Although anti-black racial disparities in U.S. police shootings have been consistently documented at the population level, new work has suggested that racial disparities in encounter-conditional use of lethal force by police are reversed relative to expectations, with police being more likely to: (1) shoot white relative to black individuals, and (2) use non-lethal as opposed to lethal force on black relative to white individuals. Encounter- and use-of-force-conditional results, however, can be misleading if the rates with which police encounter and use non-lethal force vary across officers and depend on suspect race. We find that all currently described empirical patterns in the structuring of police use-of-force—including the “reversed” racial disparities in encounter-conditional use of lethal force—are explainable under a generative model in which there are consistent and systemic biases against black individuals. If even a small subset of police more frequently encounter and use non-lethal force against black individuals than white individuals, then analyses of pooled encounter-conditional data can fail to correctly detect racial disparities in the use of lethal force. In more technical terms, statistical assessments of racial disparities conditioned on problematic intermediate variables, such as encounters, which might themselves be a causal outcome of racial bias, can produce misleading inferences. Population-level measures of use-of-force by police are more robust indicators of the overall severity of racial disparities than encounter-conditional measures—since the later neglect the differential morbidity and mortality arising from differential encounter rates. As such, population-level measures should be used when evaluating the local-level public health implications of racial disparities in police use-of-force. Research on encounter-conditional use-of-force by police can also fruitfully contribute to public policy discussions, since population-level measures alone cannot address whether racial disparities are driven by disparities in encounters or disparities in use-of-force conditional on encounters. Tests for racial biases in the encounter-conditional use of lethal force, however, must account for individual-level variation across officers in terms of race-specific encounter rates or risk falling to Simpson’s paradox.

The sub-section 2.1 of the Supplementary Information file in the original article was incorrect. This whole sub-section has now been removed.

Drawing on Skellam׳s (1958) work on sampling animal populations using transects, we derive a behavioral ecological model of the choice between sit-and-wait and active-search hunting. Using simple, biologically based assumptions about the characteristics of predator and prey, we show how an empirically definable parameter space favoring active-search hunting expands as: (1) the average rate of movement of prey decreases, or (2) the energetic costs of hunter locomotion decline. The same parameter space narrows as: (3) prey skittishness increases as a function of a hunter׳s velocity, or (4) prey become less detectable as a function of a hunter׳s velocity. Under either search tactic, encounter rate increases as a function of increasing prey velocity and increasing detection zone radius. Additionally, we investigate the roles of habitat heterogeneity and spatial auto-correlation or grouping of prey on the optimal search mode of a hunter, finding that habitat heterogeneity has the potential to complicate application of the model to some empirical examples, while the effects of prey grouping lead to relatively similar model outcomes. As predicted by the model, the introduction of the horse to the Great Plains and the introduction of the snowmobile to Arctic foraging communities decreased the metabolic costs of active-search and led to a change in normative hunting strategies that favored active-search in place of sit-and-wait hunting.

Author(s): Ross, Cody T; Mulder, Monique Borgerhoff; Oh, Seung-Yun; Bowles, Samuel; Beheim, Bret; Bunce, John; Caudell, Mark; Clark, Gregory; Colleran, Heidi; Cortez, Carmen; Draper, Patricia; Greaves, Russell D; Gurven, Michael; Headland, Thomas; Headland, Janet; Hill, Kim; Hewlett, Barry; Kaplan, Hillard S; Koster, Jeremy; Kramer, Karen; Marlowe, Frank; McElreath, Richard; Nolin, David; Quinlan, Marsha; Quinlan, Robert; Revilla-Minaya, Caissa; Scelza, Brooke; Schacht, Ryan; Shenk, Mary; Uehara, Ray; Voland, Eckart; Willfuhr, Kai; Winterhalder, Bruce; Ziker, John | Abstract: With apologies, an incorrect author list was given in the article. An additional author, Chris von Rueden, (Jepson School of Leadership Studies, University of Richmond) also contributed to this work. Author Ryan Schacht's affiliation was out-of-date. His correct affiliation is: Department of Anthropology, East Carolina University.

© 2018 The Author(s) Published by the Royal Society. All rights reserved. Monogamy appears to have become the predominant human mating system with the emergence of highly unequal agricultural populations that replaced relatively egalitarian horticultural populations, challenging the conventional idea - based on the polygyny threshold model - that polygyny should be positively associated with wealth inequality. To address this polygyny paradox, we generalize the standard polygyny threshold model to a mutual mate choice model predicting the fraction of women married polygynously. We then demonstrate two conditions that are jointly sufficient to make monogamy the predominant marriage form, even in highly unequal societies. We assess if these conditions are satisfied using individual-level data from 29 human populations. Our analysis shows that with the shift to stratified agricultural economies: (i) the population frequency of relatively poor individuals increased, increasing wealth inequality, but decreasing the frequency of individuals with sufficient wealth to secure polygynous marriage, and (ii) diminishing marginal fitness returns to additional wives prevent extremely wealthy men from obtaining as many wives as their relative wealth would otherwise predict. These conditions jointly lead to a high population-level frequency of monogamy.

We present a quantitative account based on ethnographic and documentary research of the prevalence of female genital modification (FGMo) in the African diaspora and indigenous populations of Colombia. We use these data to test hypotheses concerning the cultural evolutionary drivers of costly trait persistence, attenuation, and intergroup transmission. The uptake of FGMo by indigenous populations in Colombia is consistent with frequency-dependent hypotheses for the social transmission of the FGMo trait from the African diaspora population in the period following the era of slavery in Colombia. The prevalence and severity of practices related to FGMo decline with level of sociocultural integration into mainstream Colombian culture. Our results provide empirical support for the cultural evolutionary models proposed by Ross et al. (2015) to describe the transmission dynamics of FGMo and other costly traits. Analysis of costly trait dynamics contributes knowledge useful to applied anthropology and may be of interest in policy design and human rights monitoring in Colombia and elsewhere.

Using complementary behavioural and population ecological models, we explore the role of production risk, normal surplus and inter-annual food storage in the adaptations of societies dependent on seasonal agriculture. We find that (a) household-level, risk-sensitive adaption to unpredictable environmental variation in annual agricultural yields is a sufficient explanation for the origins of normal agrarian surplus and, consequently, of household-level incentives for inter-annual food storage; and, (b) at the population level, density-dependent Malthusian processes tightly constrain the circumstances under which this same mechanism can be effective in smoothing inter-annual fluctuations in household food availability. Greater environmental variation and higher levels of fixed set-asides such as seed requirements or transfer obligations to political authorities lead to more severe, periodic famines; however, outside of famine events, these same factors improve average population welfare by suppressing population density to levels at which Malthusian constraints have lessened impact. The combination of behavioural and population ecological modelling methods has broad and complementary potential for illustrating the dynamic properties of complex, coupled human–natural systems.

Using a sample of 40 sources reporting milpa and mucuna-intercropped maize yields in Mesoamerica, we test Boserup’s (1965) prediction that fallow is reduced as a result of growing population density. We further examine direct and indirect effects of population density on yield. We find only mixed support for Boserupian intensification. Fallow periods decrease slightly with increasing population density in this sample, but the relationship is weak. Controlling for other covariates, fallow-unadjusted maize yields first rise then fall with population density. Fallow-adjusted maize yields peak at 390 kg/ha/yr for low population densities (8 persons / km2) and decline to around 280 kg/ha/yr for the highest population densities observed in our dataset. Fallow practices do not appear to mediate the relationship between population density and yield. The multi-level modeling methods we adopt allow for data clustering, accurate estimates of group-level variation, and they generate conditional predictions, all features essential to the comparative study of prehistoric and contemporary agricultural yields.

Methods: We adopt a Bayesian framework to estimate parasite prevalence rates in 51 districts in eight Latin American countries using the disease status of 170,220 individuals tested for infection with the intestinal roundworm Ascaris lumbricoides (H€ et al., [2011]: PLoS Negl Trop Dis 5:e1404). We then use district-level estimates of parasite prevalence and individual-level social data from 5,558 individuals in the same 51 districts (Latinobar� 2008) to assess claims of causal associations between parasite prevalence and sociocultural characteristics. Results: We find, contrary to Thornhill and Fincher, that parasite prevalence is positively associated with preferences for democracy, negatively associated with preferences for collectivism, and not associated with violent crime rates or gender inequality. A positive association between parasite prevalence and religiosity, as in Fincher and Thornhill (2012: Behav Brain Sci 35:61‐79), and a negative association between parasite prevalence and achieved education, as predicted by Eppig et al. (2010: Proc R S B: Biol Sci 277:3801‐3808), become negative and unreliable when reasonable controls are included in the model. We find support for all predictions derived from our hypothesis linking structural racism to both parasite prevalence and cultural outcomes. Conclusions: We conclude that best practices in biocultural modeling require examining more than one hypothesis, retaining individual-level data and its associated variance whenever possible, and adopting multilevel techniques