Kin selection

Kin selection is evolutionary change caused by effects of behavior on the reproductive success of genetic relatives. It explains how traits that reduce an individual's reproduction can spread when they benefit relatives.

Inclusive fitness: An individual's direct and indirect contributions to the transmission of its genes to future generations. It combines an individual's own reproduction with effects on relatives that share genes.
Eusociality: A social system with cooperative brood care, overlapping generations, and reproductive division of labor. Sterile workers helping close relatives became a central case for kin-selection explanations.
W. D. Hamilton: A British evolutionary biologist who formulated inclusive fitness theory and Hamilton's rule. His 1964 papers established the mathematical framework for kin selection.
Multi-level selection: An account of evolution in which selection operates both within groups and among groups. It can describe the same social evolution that kin selection partitions through relatedness.
Hamilton's rule: A condition for altruism to be favored: relatedness times benefit exceeds the cost to the actor. It formalizes when a costly behavior toward relatives can evolve.
Honey bee: A social bee species whose colonies contain queens, workers, and drones. Haplodiploid inheritance once seemed to make worker-to-sister relatedness especially high.
George R. Price: A population geneticist who developed the Price equation and applied it to social evolution. His work gave a general mathematical description of selection among interacting individuals.
Reciprocal altruism: Cooperation in which individuals exchange benefits across interactions, often with future repayment. Unlike kin selection, it can explain cooperation between nonrelatives through repeated exchange.
Coefficient of relatedness: A measure of the probability that two individuals share an allele inherited from a common ancestor. Relatedness weights benefits to recipients in Hamilton's rule.
Alarm call: A signal that warns others of danger, sometimes exposing the caller to increased risk. Some alarm calls can protect nearby relatives while imposing costs on callers.

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