The authors argue that behavioral scientists need to stop relying primarily on Western participants, particularly Western, educated, industrialized, rich, and democratic (WEIRD) societies, for their experiments. They highlight that a significant body of evidence suggests substantial variations in cognitive and affective processes across different populations, such as in visual perception, reasoning, fairness, cooperation, memory, and IQ heritability. This diversity challenges the assumption that findings from one population can be generalized to all humans. The authors provide examples of how analytical thinking and social behaviors related to fairness differ between Western and non-Western societies. They suggest that these differences are rooted in how populations have adapted to their culturally constructed environments. The authors offer four recommendations to improve the empirical basis of theories of human behavior and psychology, including encouraging researchers to support generalizations with evidence, recognizing diverse subject pools, prioritizing cross-disciplinary and cross-cultural research, and evaluating findings across different populations. They emphasize the importance of long-term, interdisciplinary research networks to better understand human diversity and its implications for understanding human nature.The authors argue that behavioral scientists need to stop relying primarily on Western participants, particularly Western, educated, industrialized, rich, and democratic (WEIRD) societies, for their experiments. They highlight that a significant body of evidence suggests substantial variations in cognitive and affective processes across different populations, such as in visual perception, reasoning, fairness, cooperation, memory, and IQ heritability. This diversity challenges the assumption that findings from one population can be generalized to all humans. The authors provide examples of how analytical thinking and social behaviors related to fairness differ between Western and non-Western societies. They suggest that these differences are rooted in how populations have adapted to their culturally constructed environments. The authors offer four recommendations to improve the empirical basis of theories of human behavior and psychology, including encouraging researchers to support generalizations with evidence, recognizing diverse subject pools, prioritizing cross-disciplinary and cross-cultural research, and evaluating findings across different populations. They emphasize the importance of long-term, interdisciplinary research networks to better understand human diversity and its implications for understanding human nature.