Inclusive fitness (Hamilton 1964) = direct fitness + Σᵢ rᵢ·bᵢ, where rᵢ is relatedness
to recipient i and bᵢ is benefit bestowed. Unlike kin selection framing, inclusive fitness is a property
of an individual's genotype across all interactions. Direct fitness: own reproduction.
Indirect fitness: copies of your genes in relatives, weighted by r.
Together they fully account for all natural selection at a locus.