Evolutionary psychology promotes a functional conceptualization of human morality. A key insight from evolutionary studies on morality is that natural selection should favor both diversity and fluidity in morality. Moral diversity is evidenced by moral psychological research on within- and cross-society variations in the endorsement of moral concerns. Moral fluidity is exhibited in the conditional expression of moral hypocrisy, situational effects on intuitive versus rational moral processing, and environmental effects on the degree of prosociality. From this perspective, empirical methods and evolutionary models can be combined in future research to better explicate how morality develops and manifests in various environments. (PsycInfo Database Record (c) 2020 APA, all rights reserved) Public Significance Statement—From an evolutionary perspective, we review and explicate evidence of the cross-society diversity, individual differences, and within-person plasticity of moral thinking and behaviors. This view of morality as diversified and fluid potentially serves as a framework for developing interventions to prevent antisocial actions and transgressions, as well as to encourage prosocial actions and altruism.