Kin selection

Definition

An evolutionary mechanism by which a trait spreads because it increases the reproductive success of an organism's relatives, even when it reduces the actor's own direct fitness. Kin selection favors genes that promote altruistic or cooperative behaviors toward genetic relatives, with the magnitude of selection proportional to relatedness (r) and the benefit to recipients (B) relative to the cost to the actor (C), as formalized in Hamilton's rule (rB > C). The concept bridges individual and gene-level perspectives on adaptation and explains the evolution of sociality, sterility, and self-sacrifice in organisms where direct reproduction is limited or impossible.

Etymology

From kin (Middle English, of Germanic origin, meaning family or relatives) + selection (Latin selectio, from seligere, to choose). Coined by evolutionary biologists in the 1960s to distinguish selection acting through relatives from individual or group selection.

Example

In haplodiploid Hymenoptera such as honey bees (Apis mellifera), workers are more closely related to their sisters (r = 0.75) than to their own potential offspring (r = 0.5), favoring the evolution of worker sterility and cooperative brood care through kin selection. Similarly, in the eusocial naked mole-rat (Heterocephalus glaber) and many cooperative spiders (e.g., Stegodyphus dumicola), individuals forgo reproduction to raise kin, with colony genetic structure mediating the intensity of altruistic behavior.

Synonyms

• inclusive fitness selection

Related Terms

• inclusive fitness
• Hamilton's rule
• Altruism
• eusociality
• Haplodiploidy
• coefficient of relatedness
• selfish gene
• Group selection
• reciprocal altruism

Usage Notes

Often contrasted with group selection (selection among populations) and reciprocal altruism (cooperation among non-kin with expected return benefits). Kin selection operates through genetic relatedness by common descent; the broader definition including selection on shared genes regardless of ancestry is less commonly invoked in entomological literature. The term is sometimes used interchangeably with inclusive fitness theory, though purists reserve kin selection for the process and inclusive fitness for the quantity maximized. In arthropod studies, kin selection predictions are tested by manipulating relatedness (e.g., mixed versus full-sibling colonies) and measuring behavioral or fitness outcomes.