Perfect Strangers: Moral Progress, Cultural Evolution, and the Inclusivist Anomaly

How does moral progress occur? This paper develops a naturalistic account grounded in cultural evolution. We argue that modern morality emerged through institutions facilitating cooperation among increasingly extensive networks of strangers. This process introduced a novel normative infrastructure including expanded moral status, social individualism, moral egalitarianism, political liberalism, and a robust is-ought distinction. We begin by addressing why evolutionary accounts historically struggled to explain moral traits, particularly altruism and cooperation beyond kin groups. We then characterize modern morality and its key features, focusing on the puzzle of the inclusivist anomaly: the granting of moral status to individuals independently of their strategic cooperation value. Drawing on recent research on kinship intensity and institutional development, we explain how the cultural evolution of impersonal prosociality emerged from the destruction of tight kinship institutions in Western and Central Europe over 1.5 millennia. Church policies against cousin marriage, polygamy, and other kinship practices weakened intensive kinship networks, enabling new forms of cooperation among unrelated strangers. Finally, we address whether this genealogical account debunks or vindicates modern morality. We argue that understanding the contingent historical origins of modern morality need not undermine its normative authority, while acknowledging ongoing challenges to its universalization.