Correct option is C
According to Hamilton’s Rule, a gene for altruism can spread in the population if the benefit to the recipient (B), weighted by the degree of relatedness (r), is greater than the cost (C) to the altruist:
rB > C
This means altruism can evolve not only through direct fitness (personal reproduction) but also through indirect fitness (helping relatives reproduce and thus passing shared genes). The sum of these two is called inclusive fitness.
Thus, altruistic behaviour can spread if it enhances either direct fitness or indirect fitness, or both. That’s why option 3 is the most accurate and complete reflection of kin selection theory.
Information Booster:
- Direct fitness refers to genes passed on through personal reproduction.
- Indirect fitness refers to genes passed on by helping relatives reproduce.
- Inclusive fitness = direct fitness + indirect fitness.
- Hamilton’s Rule (rB > C) predicts when altruism will be favored by natural selection.
- Kin selection explains altruism among closely related individuals like siblings, parents, or cousins.
- Alarm calling in animals (e.g., ground squirrels) and eusociality in insects (e.g., bees, ants) are classic examples of kin-selected behaviour.
- This theory revolutionized understanding of how altruism can evolve despite individual cost.
Additional Information:
- Option 1 (Only direct fitness): Incorrect, as it ignores the major contribution of indirect fitness, central to kin selection.
- Option 2 (Only indirect fitness): Incomplete, as altruistic genes can also be favored via direct fitness pathways.
- Option 4 (Altruistic genes cannot spread): Incorrect. Kin selection explicitly shows how altruistic traits can spread despite reducing individual fitness, provided inclusive fitness increases.
