MENTAL MODEL · M2044

Hamilton's Rule

TechnicalHigh supportEvolutionary Biology

Included

Version 1.0.0 · Updated 2026-07-30

CORE DEFINITION

Altruistic behavior (sacrificing oneself to help others) occurs when $rB > C$. - $r$ = coefficient of relatedness (genetic similarity, siblings are 0.5) - $B$ = benefit to the recipient - $C$ = cost to the altruist -

SCAFFOLDING EFFECT

psychology

Reduce cognitive load

The cold equation of love. - This is the mathematical basis of "love" in the biological world. Why would you unhesitatingly save your child ($r=0.5$), but saving a stranger ($r \approx 0$) would

anchor

Anchor fast decisions

Altruistic behavior benefits at the genetic level when rB > C: the relatedness r times the benefit to the recipient B exceeds the cost to the altruist C, then helping relatives reproduce allows more of one's own genes to be passed on (inclusive fitness). It reduces "altruism" to a rational equation of "inclusive fitness."

MINIMUM ACTION

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Practice this model in one real situation:

When analyzing altruistic/cooperative behavior, first estimate r (relatedness), B, and C. The closer the kinship, the higher the benefit, and the lower the cost, the more likely altruism appears. This framework can be used to explain social behaviors (including human mutual aid and organizational loyalty), noting that "inclusive fitness" is not limited to blood ties.

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Source support: Explicit

link
en.wikipedia.orghttps://en.wikipedia.org/wiki/Kin_selectionZH · Explicit
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