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What the rule does not do is scale. Relatedness falls by half with each step of genealogical distance — a full sibling carries r = 0.5 , a first cousin r = 0.125 , and by the time two people are unrelated in any traceable genealogical sense, r is effectively zero. Set r 0 into Hamilton’s inequality and the right-hand side has to do all the work: either the benefit to the recipient must be extraordinary or the cost to the actor negligible, for almost every real transaction between strangers. That condition does hold for some human behavior — warning a stranger about to step in front of a car costs almost nothing and saves a great deal — but it manifestly does not hold for the…
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Equation 5 · Evolutionary Psychology
Why We Punish Strangers: The Evolution of Human Cooperation
This equation states an equality: the expressions on both sides have the same value under the article’s assumptions.
What the rule does not do is scale. Relatedness falls by half with each step of genealogical distance — a full sibling carries r = 0.5 , a first cousin r = 0.125 , and by the time two people are unrelated in any traceable genealogical sense, r is effectively zero. Set r 0 into Hamilton’s inequality and the right-hand side has to do all the work: either the benefit to the recipient must be extraordinary or the cost to the actor negligible, for almost every real transaction between strangers. That condition does hold for some human behavior — warning a stranger about to step in front of a car costs almost nothing and saves a great deal — but it manifestly does not hold for the…