The standard view in evolutionary anthropology is that human morality originated as an adaptation for solving problems of social living that early humans faced in the Pleistocene. This descriptive claim has been invoked to support the normative thesis of Ethical Pluralism (EP): the view that there is more than one valid morality. The logic is that if the justifiability of a moral system depends on how well it performs certain social functions, and if different human cultural ecologies call for different functional moralities, then at least a moderate version of EP may be true.
In this paper, we show that this simple evolutionary defense of EP fails because there is a yawning gap between a morality’s validity and its success in “solving problems of social living,” even if these functional solutions are not tied to effects on reproductive fitness. Although morality originated as an adaptation to solve certain problems of social living, it has since come to encompass features that are not explainable in any functionalist terms. We go on to construct a richer evolutionary argument for EP, one that draws upon two non-adaptive concepts from evolutionary biology: (1) the dynamic of plasticity paired with later rigidity in individual moral development, and (2) path-dependent constraints on the evolution of moral systems in which individual moral development occurs.
Taken together, these two phenomena suggest that there is more than one way of flourishing for human beings—and if conduciveness to flourishing or wellbeing is one plausible criterion for evaluating moralities, then it is likely that there is more than one valid morality. Finally, we examine the implications of this discussion for ideal moral theory. We conclude that even if there were only one uniquely valid moral theory, this would still be compatible with EP, given path-dependent constraints on the evolution of moralities.