The global geography of human subsistence

Climate, climate change and the global diversity of human houses

Globally, human house types are diverse, varying in shape, size, roof type, building materials, arrangement, decoration and many other features. Here we offer the first rigorous, global evaluation of the factors that influence the construction of traditional (vernacular) houses. We apply macroecological approaches to analyse data describing house features from 1900 to 1950 across 1000 societies. Geographic, social and linguistic descriptors for each society were used to test the extent to which key architectural features may be explained by the biophysical environment, social traits, house features of neighbouring societies or cultural history. We find strong evidence that some aspects of the climate shape house architecture, including floor height, wall material and roof shape. Other features, particularly ground plan, appear to also be influenced by social attributes of societies, such as whether a society is nomadic, polygynous or politically complex. Additional variation in all house features was predicted both by the practices of neighouring societies and by a society's language family. Collectively, the findings from our analyses suggest those conditions under which traditional houses offer solutions to architects seeking to reimagine houses in light of warmer, wetter or more variable climates.

Humanity's diverse predatory niche and its ecological consequences

Although humans have long been predators with enduring nutritive and cultural relationships with their prey, seldom have conservation ecologists considered the divergent predatory behavior of contemporary, industrialized humans. Recognizing that the number, strength and diversity of predator-prey relationships can profoundly influence biodiversity, here we analyze humanity's modern day predatory interactions with vertebrates and estimate their ecological consequences. Analysing IUCN 'use and trade' data for ~47,000 species, we show that fishers, hunters and other animal collectors prey on more than a third (~15,000 species) of Earth's vertebrates. Assessed over equivalent ranges, humans exploit up to 300 times more species than comparable non-human predators. Exploitation for the pet trade, medicine, and other uses now affects almost as many species as those targeted for food consumption, and almost 40% of exploited species are threatened by human use. Trait space analyses show that birds and mammals threatened by exploitation occupy a disproportionally large and unique region of ecological trait space, now at risk of loss. These patterns suggest far more species are subject to human-imposed ecological (e.g., landscapes of fear) and evolutionary (e.g., harvest selection) processes than previously considered. Moreover, continued overexploitation will likely bear profound consequences for biodiversity and ecosystem function.

From Food to Gods to Food to Waste

The present global food waste problem threatens food systems sustainability and our planet. The generation of food waste stems from the interacting factors of the need for food production, food access and availability, motivations and ignorance around food purchase and consumption, and market constraints. Food waste has increased over time. This is related to the change in how humans value food through the generations and altered human food consumption and food discard behaviors. There is also a lack of understanding of the impacts of current food production, processing and consumption patterns on food waste creation. This review examines the cultural, religious, social and economic factors influencing attitudes to food and their effects on food waste generation. The lessons from history about how humans strove toward zero waste are covered. We review the important drivers of food waste: waste for profit, food diversion to feed, waste for convenience, labeling, food service waste and household food waste. We discuss strategies for food waste reduction: recovery of food and food ingredients, waste conversion to energy and food, reducing waste from production/processing and reducing consumer food waste, and emphasize the need for all stakeholders to work together to reduce food waste.

Pathways to social inequality

Social inequality is ubiquitous in contemporary human societies, and has deleterious social and ecological impacts. However, the factors that shape the emergence and maintenance of inequality remain widely debated. Here we conduct a global analysis of pathways to inequality by comparing 408 non-industrial societies in the anthropological record (described largely between 1860 and 1960) that vary in degree of inequality. We apply structural equation modelling to open-access environmental and ethnographic data and explore two alternative models varying in the links among factors proposed by prior literature, including environmental conditions, resource intensification, wealth transmission, population size and a well-documented form of inequality: social class hierarchies. We found support for a model in which the probability of social class hierarchies is associated directly with increases in population size, the propensity to use intensive agriculture and domesticated large mammals, unigeniture inheritance of real property and hereditary political succession. We suggest that influence of environmental variables on inequality is mediated by measures of resource intensification, which, in turn, may influence inequality directly or indirectly via effects on wealth transmission variables. Overall, we conclude that in our analysis a complex network of effects are associated with social class hierarchies.

The potential to infer the historical pattern of cultural macroevolution

Phylogenetic analyses increasingly take centre-stage in our understanding of the processes shaping patterns of cultural diversity and cultural evolution over time. Just as biologists explain the origins and maintenance of trait differences among organisms using phylogenetic methods, so anthropologists studying cultural macroevolutionary processes use phylogenetic methods to uncover the history of human populations and the dynamics of culturally transmitted traits. In this paper, we revisit concerns with the validity of these methods. Specifically, we use simulations to reveal how properties of the sample (size, missing data), properties of the tree (shape) and properties of the traits (rate of change, number of variants, transmission mode) might influence the inferences that can be drawn about trait distributions across a given phylogeny and the power to discern alternative histories. Our approach shows that in two example datasets specific combinations of properties of the sample, of the tree and of the trait can lead to potentially high rates of Type I and Type II errors. We offer this simulation tool to help assess the potential impact of this list of persistent perils in future cultural macroevolutionary work. This article is part of the theme issue 'Foundations of cultural evolution'.

Psychology as a Historical Science

Psychology has traditionally seen itself as the science of universal human cognition, but it has only recently begun seriously grappling with cross-cultural variation. Here we argue that the roots of cross-cultural variation often lie in the past. Therefore, to understand not only how but also why psychology varies, we need to grapple with cross-temporal variation. The traces of past human cognition accessible through historical texts and artifacts can serve as a valuable, and almost completely unutilized, source of psychological data. These data from dead minds open up an untapped and highly diverse subject pool. We review examples of research that may be classified as historical psychology, introduce sources of historical data and methods for analyzing them, explain the critical role of theory, and discuss how psychologists can add historical depth and nuance to their work. Psychology needs to become a historical science if it wants to be a genuinely universal science of human cognition and behavior.

Cultural transmission and ecological opportunity jointly shaped global patterns of reliance on agriculture

The evolution of agriculture improved food security and enabled significant increases in the size and complexity of human groups. Despite these positive effects, some societies never adopted these practices, became only partially reliant on them, or even reverted to foraging after temporarily adopting them. Given the critical importance of climate and biotic interactions for modern agriculture, it seems likely that ecological conditions could have played a major role in determining the degree to which different societies adopted farming. However, this seemingly simple proposition has been surprisingly difficult to prove and is currently controversial. Here, we investigate how recent agricultural practices relate both to contemporary ecological opportunities and the suitability of local environments for the first species domesticated by humans. Leveraging a globally distributed dataset on 1,291 traditional societies, we show that after accounting for the effects of cultural transmission and more current ecological opportunities, levels of reliance on farming continue to be predicted by the opportunities local ecologies provided to the first human domesticates even after centuries of cultural evolution. Based on the details of our models, we conclude that ecology probably helped shape the geography of agriculture by biasing both human movement and the human-assisted dispersal of domesticates.

The emergence of locally adaptive institutions: Insights from traditional social structures of East African pastoralists

Humans inhabit the widest range of ecological and social niches of any mammal. Yet each ecological and social environment presents a set of challenges that we must solve in order to successfully inhabit it. We are able to do so by building institutions that can flexibly respond to changing circumstances. Institutions that solve adaptive challenges necessary for human sociality, such as how to resolve conflicts, find mates, and extract and distribute resources, are termed locally adaptive institutions. The design of locally adaptive institutions promotes coordination and cooperation among unrelated individuals, reflecting the constraints of the particular ecological and social challenges to which they are responsive. Institutions generally are enabled by a suite of social and psychological mechanisms, including norm compliance, self-interested design, selective imitation, and cultural group selection among others. The development of locally adaptive institutions are likely to be especially shaped by self-interested design in which agents are sensitive to the payoffs from various norms and choose to enforce and follow those which they anticipate to be most beneficial to themselves. Exogenous shocks, including the advent of material and cultural technologies, population pressures, or even group conflict can contribute to the modification of existing social institutions and the development of new social structures. Using several case examples from traditional east African pastoralist societies, I illustrate how ecological and social pressures shape the development of social norms that underlie locally adaptive social institutions and facilitate continued cooperation in the face of change at scales ranging from local to global.

Cultural influences on word meanings revealed through large-scale semantic alignment

If the structure of language vocabularies mirrors the structure of natural divisions that are universally perceived, then the meanings of words in different languages should closely align. By contrast, if shared word meanings are a product of shared culture, history and geography, they may differ between languages in substantial but predictable ways. Here, we analysed the semantic neighbourhoods of 1,010 meanings in 41 languages. The most-aligned words were from semantic domains with high internal structure (number, quantity and kinship). Words denoting natural kinds, common actions and artefacts aligned much less well. Languages that are more geographically proximate, more historically related and/or spoken by more-similar cultures had more aligned word meanings. These results provide evidence that the meanings of common words vary in ways that reflect the culture, history and geography of their users.

Cultural group selection and human cooperation: a conceptual and empirical review

Cultural group selection has been proposed as an explanation for humans' highly cooperative nature. This theory argues that social learning mechanisms, combined with rewards and punishment, can stabilise any group behaviour, cooperative or not. Equilibrium selection can then operate, resulting in cooperative groups outcompeting less-cooperative groups. This process may explain the widespread cooperation between non-kin observed in humans, which is sometimes claimed to be altruistic. This review explores the assumptions of cultural group selection to assess whether it provides a convincing explanation for human cooperation. Although competition between cultural groups certainly occurs, it is unclear whether this process depends on specific social learning mechanisms (e.g. conformism) or a norm psychology (to indiscriminately punish norm-violators) to stabilise groups at different equilibria as proposed by existing cultural group selection models. Rather than unquestioningly adopt group norms and institutions, individuals and groups appear to evaluate, design and shape them for self-interested reasons (where possible). As individual fitness is frequently tied to group fitness, this often coincides with constructing group-beneficial norms and institutions, especially when groups are in conflict. While culture is a vital component underlying our species' success, the extent to which current conceptions of cultural group selection reflect human cooperative evolution remains unclear.

The ecological drivers of variation in global language diversity

Language diversity is distributed unevenly over the globe. Intriguingly, patterns of language diversity resemble biodiversity patterns, leading to suggestions that similar mechanisms may underlie both linguistic and biological diversification. Here we present the first global analysis of language diversity that compares the relative importance of two key ecological mechanisms - isolation and ecological risk - after correcting for spatial autocorrelation and phylogenetic non-independence. We find significant effects of climate on language diversity, consistent with the ecological risk hypothesis that areas of high year-round productivity lead to more languages by supporting human cultural groups with smaller distributions. Climate has a much stronger effect on language diversity than landscape features, such as altitudinal range and river density, which might contribute to isolation of cultural groups. The association between biodiversity and language diversity appears to be an incidental effect of their covariation with climate, rather than a causal link between the two.