Kin selection
Also known as: Inclusive fitness
Helping relatives spreads your genes, so altruism toward kin can evolve.
What it means
An evolutionary explanation for altruism in which a behavior that reduces an individual's own reproduction can still spread if it sufficiently benefits genetic relatives who share the same genes. Hamilton's rule states the condition precisely: altruism is favored when the relatedness between actor and recipient, times the benefit to the recipient, exceeds the cost to the actor (rb > c). It reframes the unit of selection from the individual to the gene and resolves the long-standing puzzle of self-sacrifice in social animals. It matters as a foundational pillar of cooperation theory in biology and a baseline against which uniquely human cooperation among non-kin is measured.
Examples
A ground squirrel gives an alarm call that endangers itself but warns nearby siblings and offspring carrying its genes.
A worker bee never reproduces yet spends her life feeding the queen's larvae — those larvae are her sisters, carrying her genes, so the labour still pays.
A grandmother who bankrolls her grandchildren's education gains nothing reproductively herself, but Hamilton's rule still counts the genes she shares with them.
First described in W. D. Hamilton (1964); J. B. S. Haldane.