Equation 13 · Part 3 · Why We Punish Strangers: The Evolution of Human Cooperation
Symbol x
What this part means
the writing.
Its job in the formula
x is one of the signed contributions combined to compute the quantity on the left.
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Where the article explains it
Writing x for the frequency of cooperators, y for the frequency of punishers, and k for the cost of punishing a single defector, the punisher’s expected fitness penalty is approximately .
The passage around this formula
…defectors become rare within a group, the punisher’s fitness disadvantage relative to a non-punishing cooperator shrinks toward zero even while the plain cooperator’s disadvantage relative to a defector does not. Writing x for the frequency of cooperators, y for the frequency of punishers, and k for the cost of punishing a single defector, the punisher’s expected fitness penalty is approximately . which falls as the residual pool of defectors, 1 - x - y , shrinks. Once a group happens to reach a…
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Sources cited in the surrounding passage
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