Broadening horizons: Sample diversity and socioecological theory are essential to the future of psychological science.

The present lack of sample diversity and ecological theory in psychological science fundamentally limits generalizability and obstructs scientific progress. A focus on the role of socioecology in shaping the evolution of morphology, physiology, and behavior has not yet been widely applied toward psychology. To date, evolutionary approaches to psychology have focused more on finding universals than explaining variability. However, contrasts between small-scale, kin-based rural subsistence societies and large-scale urban, market-based populations, have not been well appreciated. Nor has the variability within high-income countries, or the socioeconomic and cultural transformations affecting even the most remote tribal populations today. Elucidating the causes and effects of such broad changes on psychology and behavior is a fundamental concern of the social sciences; expanding study participants beyond students and other convenience samples is necessary to improve understanding of flexible psychological reaction norms among and within populations. Here I highlight two examples demonstrating how socioecological variability can help explain psychological trait expression: () the role of environmental harshness and unpredictability on shaping time preference and related traits, such as impulsivity, vigilance, and self-efficacy; and () the effects of industrialization, market integration, and niche complexity on personality structure. These cases illustrate how appropriate theory can be a powerful tool to help determine choices of diverse study populations and improve the social sciences.