Work time and market integration in the original affluent society.

Does integration into commercial markets lead people to work longer hours? Does this mean that people in more subsistence-oriented societies work less compared to those in more market-integrated societies? Despite their venerable status in both anthropology and economic history, these questions have been difficult to address due to a dearth of appropriate data. Here, we tackle the issue by combining high-quality time allocation datasets from 8 small-scale populations around the world (45,019 observations of 863 adults) with similar aggregate data from 14 industrialized (Organisation for Economic Co-operation and Development) countries. Both within and across societies, we find evidence of a positive correlation between work time and market engagement for men, although not for women. Shifting to fully commercial labor is associated with an increase in men's work from around 45 h per week to 55 h, on average; women's work remains at nearly 55 h per week across the spectrum. These results inform us about the socioeconomic determinants of time allocation across a wider range of human societies.

The Cultural Brain Hypothesis: How culture drives brain expansion, sociality, and life history.

In the last few million years, the hominin brain more than tripled in size. Comparisons across evolutionary lineages suggest that this expansion may be part of a broader trend toward larger, more complex brains in many taxa. Efforts to understand the evolutionary forces driving brain expansion have focused on climatic, ecological, and social factors. Here, building on existing research on learning, we analytically and computationally model the predictions of two closely related hypotheses: The Cultural Brain Hypothesis and the Cumulative Cultural Brain Hypothesis. The Cultural Brain Hypothesis posits that brains have been selected for their ability to store and manage information, acquired through asocial or social learning. The model of the Cultural Brain Hypothesis reveals relationships between brain size, group size, innovation, social learning, mating structures, and the length of the juvenile period that are supported by the existing empirical literature. From this model, we derive a set of predictions-the Cumulative Cultural Brain Hypothesis-for the conditions that favor an autocatalytic take-off characteristic of human evolution. This narrow evolutionary pathway, created by cumulative cultural evolution, may help explain the rapid expansion of human brains and other aspects of our species' life history and psychology.

Unselective Overimitators: The Evolutionary Implications of Children's Indiscriminate Copying of Successful and Prestigious Models.

Children are both shrewd about whom to copy-they selectively learn from certain adults-and overimitators-they copy adults' obviously superfluous actions. Is overimitation also selective? Does selectivity change with age? In two experiments, 161 two- to seven-year-old children saw videos of one adult receiving better payoffs or more bystander attention than another. Children then watched the adults perform unnecessary actions on novel transparent devices. Children preferred the adult who received greater payoffs or bystander attention when asked questions like "Who do you think is smarter?" but overimitated both adults' unnecessary actions equally. Although older children overimitated more, unselectivity was consistent across ages. This pattern hints at a plausible adaptive function of overimitation: acquiring rarely demonstrated behaviors by practising them immediately.

The Big Man Mechanism: how prestige fosters cooperation and creates prosocial leaders.

Anthropological evidence from diverse societies suggests that prestige-based leadership may provide a foundation for cooperation in many contexts. Here, inspired by such ethnographic observations and building on a foundation of existing research on the evolution of prestige, we develop a set of formal models to explore when an evolved prestige psychology might drive the cultural evolution of n-person cooperation, and how such a cultural evolutionary process might create novel selection pressures for genes that make prestigious individuals more prosocial. Our results reveal (i) how prestige can foster the cultural emergence of cooperation by generating correlated behavioural phenotypes, both between leaders and followers, and among followers; (ii) why, in the wake of cultural evolution, natural selection favours genes that make prestigious leaders more prosocial, but only when groups are relatively small; and (iii), why the effectiveness of status differences in generating cooperation in large groups depends on cultural transmission (and not primarily on deference or coercion). Our theoretical framework, and the specific predictions made by these models, sketch out an interdisciplinary research programme that cross-cuts anthropology, biology, psychology and economics. Some of our predictions find support from laboratory work in behavioural economics and are consistent with several real-world patterns.

Tackling group-level traits by starting at the start.

We agree that emergent group-level properties are important; however, we disagree that current approaches, especially culture-gene coevolutionary (CGC) approaches, have neglected them. We explain how CGC helps demystify the tumult of humans' group-level complexity by "starting at the start," and why (a) assuming undifferentiated individuals and (b) focusing on cooperation are actually powerful tools to this end.

Understanding the research program.

The target article misunderstands the research program it criticizes. The work of Boyd, Richerson, Fehr, Gintis, Bowles and their collaborators has long included the theoretical and empirical study of models both with and without diffuse costly punishment. In triaging the situation, we aim to (1) clarify the theoretical landscape, (2) highlight key points of agreement, and (3) suggest a more productive line of debate.

The prevalence of mind-body dualism in early China.

We present the first large-scale, quantitative examination of mind and body concepts in a set of historical sources by measuring the predictions of folk mind-body dualism against the surviving textual corpus of pre-Qin (pre-221 BCE) China. Our textual analysis found clear patterns in the historically evolving reference of the word xin (heart/heart-mind): It alone of the organs was regularly contrasted with the physical body, and during the Warring States period it became less associated with emotions and increasingly portrayed as the unique locus of "higher" cognitive abilities. We interpret this as a semantic shift toward a shared cognitive bias in response to a vast and rapid expansion of literacy. Our study helps test the proposed universality of folk dualism, adds a new quantitative approach to the methods used in the humanities, and opens up a new and valuable data source for cognitive scientists: the record of dead minds.

Culture-gene coevolution, norm-psychology and the emergence of human prosociality.

Diverse lines of theoretical and empirical research are converging on the notion that human evolution has been substantially influenced by the interaction of our cultural and genetic inheritance systems. The application of this culture-gene coevolutionary approach to understanding human social psychology has generated novel insights into the cognitive and affective foundations of large-scale cooperation, social norms and ethnicity. This approach hypothesizes a norm-psychology: a suite of psychological adaptations for inferring, encoding in memory, adhering to, enforcing and redressing violations of the shared behavioral standards of one's community. After reviewing the substantial body of formal theory underpinning these predictions, we outline how this account organizes diverse empirical findings in the cognitive sciences and related disciplines. Norm-psychology offers explanatory traction on the evolved psychological mechanisms that underlie cultural evolution, cross-cultural differences and the emergence of norms.

Evidence for a sensitive period for acculturation: younger immigrants report acculturating at a faster rate.

Though recent adult immigrants often seem less acculturated to their new society than people who immigrated as children, it is not clear whether this difference is driven by duration of exposure or exposure during a sensitive developmental period. In a study aimed at disambiguating these influences, community and student samples of Hong Kong immigrants to Vancouver, Canada, completed the Vancouver Index of Acculturation, a measure that assesses respondents' identification with their mainstream and heritage cultures. A longer duration of exposure was found to be associated with greater identification with Canadian culture only at younger ages of immigration, but not at later ages of immigration. Conversely, identification with Chinese culture was unaffected by either age of immigration or length of exposure to Canadian culture. These findings provide evidence for a sensitive period for acculturation: People are better able to identify with a host culture the longer their exposure to it, but only if this exposure occurs when they are relatively young.