Robert L. Trivers (1971), The Quarterly Review of Biology 46(1): 35–57 — DOI-10.1086/406755
Key takeaways
- Altruism between non-kin can be favoured by selection when the benefit to the recipient exceeds the cost to the giver, the same individuals meet many times, they are exposed to such situations roughly symmetrically, and altruists curtail help to non-reciprocators (The Model).
- Moral emotions have functions: moralistic aggression protects the altruist against cheaters, gratitude and sympathy track the cost/benefit ratio of acts, guilt motivates reparation once cheating is discovered, and selection then favours sham versions of each and the ability to detect them (pp. 47–53).
- With language, multiparty systems can detect cheating as “infraction of … a rule of conduct”: “selection may favor the elaboration of norms of reciprocal conduct” (p. 52).
Standing in the record
Filed on 2026-10-02 at the owner’s request, as one of the evolutionary sources of morality-as-cooperation. The lineage paragraph of NOTE-034 names “reciprocal altruism (Trivers)” second, and Curry’s 2016 statement of the theory (LIT-503) cites it, with Axelrod, for its exchange domain.
NOTE-402 is the close reading of 2026-10-02, and it placed the work: Active. Of the biological sources of morality-as-cooperation it is the one that is itself about morality. Its human section gives an adaptive function to moralistic aggression, guilt, gratitude and sympathy and to the detection of their counterfeits, and predicts that rules of reciprocal conduct will be elaborated once language allows multiparty enforcement.
What it grounds is the exchange domain, and it gives that domain more than morality-as-cooperation later uses: an account of the moral emotions that regulate exchange. The “injustice, unfairness” it discusses is inequity in exchange (subtle cheating, unequal food-sharing), not the division of a disputed resource that MAC calls fairness. Its remarks on dominance and aid in combat are preconditions for reciprocity, not an account of hawkish or dovish displays. Its “multiparty” and “generalized altruism” passages are the seed of indirect reciprocity, which Alexander (LIT-495) made the basis of moral systems and Nowak (LIT-501) gave a rule.
Two further connections. Reciprocity is what Tomasello’s account of obligation (LIT-125) argues cannot generate obligation (claim C6 of its reading, NOTE-185): Trivers’s guilt is reparation to keep an exchange going, Tomasello’s obligation is pressure from a joint “we”. And Fitouchi, André & Baumard’s moral disciplining (LIT-101) rests on the premise that reciprocal cooperation requires delaying gratification (assumption A1 of its reading, NOTE-132), which is Trivers’s time lag between giving and return.
Topic. natural-sciences first: the model and two of its three cases
are animal biology. moral-psychology because the human section is an
account of moral emotion and norms and their evolution, which is that
word’s blurb; it is second because the paper’s own subject is the
evolution of altruism, and “cheating” is used “solely for convenience …
no conscious intent or moral connotation is implied” (p. 36).
emotion-and-affect for the functional account of gratitude, sympathy,
guilt and liking. social-science for its use of the experimental and
ethnographic literature on human reciprocity.
Anthology. No instruction for machine-learning practice; not held there.