Group-level selection favors tribes whose members sacrifice for the common good

Evidence

Put another way, when competition between groups is intense, and when other factors such as war technology and population size are similar, groups that happen to have members who acquire traits favoring self-sacrifice and subordinate self-interest for group interests—that is, groups with stronger social solidarity—will tend to win out. Of course, when a whole group wins out, the individuals in that group win out as well, and the self-sacrificial strategies that led to their groups’ success spread. … It must not be forgotten that although a high standard of morality gives but a slight or no advantage to each individual man and his children over the other men of the same tribe, yet that an advancement in the standard of morality and an increase in the number of well-endowed men will certainly give an immense advantage to one tribe over another. There can be no doubt that a tribe including many members who, from possessing in a high degree the spirit of patriotism, fidelity, obedience, courage, and sympathy, were always ready to give aid to each other and to sacrifice themselves for the common good, would be victorious over other tribes; and this would be natural selection. — Norenzayan, Ara, Big gods - how religion transformed…, 453

Categorization

• XREF: Group-selection mechanism that predicts which religious communities survive — ties to partner-choice logic for why sacrifice signals pay off. — connects to: Human sacrifice was rational necessity when groups could only survive by eating human flesh; Sacred-value commitment produces costly sacrifice that lets weak groups beat stronger foes. — Scott Atran, The Devoted Actor: Unconditional…, 1; States co-opt evolved kin and in-group tendencies to manufacture devoted actors. — Scott Atran, The Devoted Actor: Unconditional…, 27 (+1 more)
• BMF: Tribe-level selection via self-sacrifice for the common good evokes the clan dynamics in Things Fall Apart — where Umuofia’s solidarity-driven strength and its erosion under colonial pressure hinge on exactly this kind of collective self-sacrifice.