Kin selection
Summary
Kin selection is the evolutionary idea that a behavior costly to the individual can spread if it helps genetic relatives survive and reproduce, raising inclusive fitness. Testable point: help is predicted to be greater toward closer kin, when rB > C (Hamilton's rule).
Detail
Meaning: Kin selection is natural selection favoring behavior that helps genetic relatives survive and reproduce, even when it costs the helper. Relatives share copies of genes, so helping them can raise the helper's inclusive fitness (its own offspring plus its effect on relatives' offspring). It is a major evolutionary explanation for altruism such as alarm calls, sterile worker insects, and helping raise siblings' young.
Equation: rB > C, where r is the coefficient of relatedness (unitless, 0 to 1), B is the fitness benefit to the recipient, and C is the fitness cost to the actor (both in offspring, unitless count). Helping is favored when rB exceeds C.
On the MCAT: A passage describes an animal that helps or warns others, and you predict who gets the most help. Expect more help toward closer kin: r is 0.5 for parent–child and full siblings, 0.25 for half siblings and grandparent–grandchild, and 0.125 for first cousins.
Common confusion: Kin selection does not require conscious choice, and it is not behavior for the good of the species; it follows from shared genes. Helping unrelated individuals for a later return is reciprocal altruism, a separate account.
Sources
- Campbell Biology
- Exploring Psychology
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.