Equation 13 · Part 2 · Why We Punish Strangers: The Evolution of Human Cooperation
Symbol k
What this part means
k is one of the signed contributions combined to compute the quantity on the left.
Its job in the formula
k is one of the signed contributions combined to compute the quantity on the left.
Full expression→Symbol k→Article meaning
The passage around this formula
…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 state where
Learn the underlying idea
A function assigns an output to each allowed input. The expression f(x) means “apply f to x”.
Open the illustrated functions: inputs become outputs guide →
See this notation across published equations →
Sources cited in the surrounding passage
These citations provide research context; check each source for the exact claim it supports.