I propose that we consider a trait natural to an individual just in case it arises in that individual through a normal process of development in a normal, nutritive environment, rather than as a result of injury, acquired disease, malnutrition, or (especially) external imposition.
With this understanding of the “natural” in hand, let me reframe the key idea of the previous section. A relatively stable social system is part of a normal, nutritive environment for human beings (and for all social animals).
The core question on which they disagree, I would suggest, is this: Is morality something imposed on people from outside (Xunzi) or something that arises in the normal process of human development if people are encouraged to reflect for themselves (Mencius)? In other words, is moral development a process more of indoctrination or self-discovery?
Besides the researchers on moral development cited above who seem to favor views roughly of this sort, let me mention the work on early childhood sympathy by Zahn-Waxler and others; de Waal’s work on the origins of morality in non-human primates; Arendt’s suggestion that evil tends to flow from a failure to think in her study of Eichmann; and work on juvenile delinquency that suggests reduced recidivism when offenders are encouraged to reflect.