Income and Sex Moderate the Association Between Population Density and Reproduction: A Multilevel Analysis of Life History Strategies Across 23 Nations.

While previous studies guided by evolutionary life history theory have revealed several important socioecological moderators of the influence of population density (PD) on reproduction, absent is an understanding of how individual-level factors such as personal resources and sex differences might interact and play a role. Using data from a large sample of clients (N = 4,432,440) of an online dating company spanning 317 states nested within 23 countries, we contributed a robust multilevel analysis of life history effects by assessing the interaction between state-level PD and individual-level income on offspring quantity, and we further qualified this analysis by sex. Consistent with previous research, PD was negatively correlated with having children. Consistent with our novel hypotheses, this negative relationship was moderated by income such that the link between PD and low fertility became weaker with increasing levels of income and these patterns were stronger for men than for women. These results held despite controlling for a variety of country-level, state-level, and individual-level confounds. Findings are discussed together with theoretical and practical implications for the management of fertility based on evolutionary life history perspectives.

Stunted upward mobility in a learning environment reduces the academic benefits of growth mindsets.

Does stunted upward mobility in an educational system impede beneficial psychological processes of learning? We predicted that growth mindsets of intelligence, a well-established psychological stimulant to learning, would be less potent in low-mobility, as compared to high-mobility, learning environments. An analysis of a large cross-national dataset and a longitudinal experiment accumulated converging evidence for this hypothesis. Study 1 examined data from 15-y-old students across 30 countries (n = 235,141 persons). Replicating past findings, growth mindsets positively predicted students' math, science, and reading literacy. More importantly, the country-level indicator of educational mobility (i.e., the percentage of children from low-education households to graduate from tertiary education) moderated the effect of growth mindsets. Depending on the subject, the gain in predicted academic performance from a one-unit increase in growth mindsets was reduced by 42 to 45% from a high-mobility to a low-mobility country. Results were robust with or without important covariates. Study 2 experimentally manipulated people's perception of mobility in a carefully constructed learning environment. The moderating role of educational mobility was replicated and extended to learning behavior, which subsequently predicted performance. Evidence further suggests that in high-mobility environments, both advantaged and disadvantaged learners benefited from growth mindsets, albeit likely through diverging mechanisms; when the effect of growth mindsets was attenuated in low-mobility environments, the potential for the disadvantaged to overcome the performance gap was also limited. Implications for galvanizing the upward mobility of the disadvantaged, evaluating the effectiveness of mindset interventions, and conceptualizing social mobility from a psychological perspective are discussed.