Which concept explains that an individual's fitness can be enhanced by the success of relatives?

• A. Inclusive fitness
• B. Kin selection
• C. Direct fitness
• D. Group selection

Answer: (A)

Inclusive fitness captures the idea that an individual's genetic success comes from both its own offspring and the impact it has on the reproduction of relatives who share genes with it. Because relatives carry copies of your genes, helping them survive and reproduce can spread your genes even if you don’t produce many offspring yourself. This idea is formalized by Hamilton’s rule, which says altruism is favored when the relatedness to the recipient times the benefit to them exceeds the cost to the actor (rB > C). For example, a worker bee or a caregiving relative may boost their own genetic legacy by helping relatives reproduce, rather than by reproducing themselves. Direct fitness counts only personal offspring, while group selection is a separate concept about group-level advantages. Kin selection explains the mechanism behind inclusive fitness, but the overarching concept describing fitness gains from relatives’ success is inclusive fitness.