Practice question

Altruism reduces the actor's direct fitness while increasing the recipient's fitness, giving a (-,+) actor-recipient outcome. It can evolve when indirect fitness benefits compensate for the cost, as formalized by Hamilton's rule: related recipients may carry copies of the same alleles, so helping them can increase inclusive fitness. Reciprocal interactions, reputation, and group-structured processes can also maintain apparently altruistic behavior under particular conditions. This differs from mutual benefit, selfish behavior in which the actor gains while another loses, and spite in which both pay costs. The classification concerns fitness consequences rather than conscious intention, making it applicable to behaviors ranging from alarm calls to sterile worker assistance. Ecological categories are simplified models, yet they remain valuable when their assumptions are stated. The selected description captures the dominant net effect, while real systems may vary with density, habitat, life stage, and environmental conditions. This reasoning connects organismal behavior with broader ecological consequences. A mechanism that changes encounter rates, resource use, or reproductive success can scale up to alter population trajectories and the structure of species interactions.