We argue that although objectivist moral attitudes may facilitate cooperation, they are not necessary for the high levels of cooperation in humans. This is implied by evolutionary models that articulate a mechanism underlying Stanford's account, and is also suggested by the ability of merely conventional social norms to explain extreme human behaviors.
Handfield, Toby, John Thrasher, and Julian García. "Greenbeards and Signaling: Why Morality isn't Indispensable." Behavioral and Brain Sciences, vol. 41, 2018, e103. DOI: 10.1017/S0140525X18000080
Cambridge University Press