Hamilton’s Rule, explained.
Hamilton’s rule gives a marginal condition favouring a social act when relatedness-weighted reproductive benefit exceeds reproductive cost: rB > C.
Why it happens
Five stipulated acts supply r, B and C. The player predicts whether each passes the simple condition, then inspects rB−C and the actual prediction ledger.
Hamilton’s rule gives a marginal condition favouring a social act when relatedness-weighted reproductive benefit exceeds reproductive cost: rB > C.
Read the result
Correct classifications refer only to the supplied marginal fitness condition. They are not ethical scores or predictions about what a person will choose.
A worked example
Compare relatedness-weighted benefit with cost
For the first act multiply relatedness one-half by benefit three.
Compare 1.5 with cost one and classify the simple condition as favouring the act.
Contrast the one-eighth-relatedness act with benefit four and cost one, where the weighted benefit is only one-half.
OPTIONAL DEEPER DETAILGo deeper: inside the model
Inside this model
Five stipulated acts supply r, B and C. The player predicts whether each passes the simple condition, then inspects rB−C and the actual prediction ledger.
Where this idea is useful
A practical use
Separate a biological fitness comparison from a moral claim that people ought to help only relatives.
A common misconception
“Hamilton’s rule is a moral instruction to favour family.”
The inequality is a biological reproductive-fitness condition under assumptions; it does not determine moral obligations or human motives.
What this explanation leaves out
- Comparable marginal reproductive effects and the stated relatedness measure are assumed. Nonadditive effects and complex population structure require care beyond this exercise.
Why are B and C not measured in money?
They represent stipulated comparable marginal reproductive effects, not personal utility or a household financial payoff.
Are the benefit, cost and relatedness defined on compatible biological terms?
Associated thinkers
Associations marked provisional are awaiting source review.
Further reading
Explore the original research or the teaching reference behind this experiment.