Final answer:
Selection may favor traits that reduce an individual's direct fitness if this leads to increased shared genetic success within a related population, a concept known as kin selection. This is apparent in the altruistic behaviors of social insects where certain actions benefit the reproductive success of relatives, ensuring the propagation of shared genes.
Step-by-step explanation:
Selection could favor traits that result in decreased personal fitness if certain social and genetic conditions are met. One such condition is kin selection, where behaviors that are seemingly detrimental to the individual's direct fitness could actually promote the passing of shared genes. This occurs when the cost to the actor is outweighed by the significantly higher benefit to the recipient who is closely related (a high coefficient of relatedness). Therefore, altruistic behavior can evolve because it increases inclusive fitness—the total effect an individual's actions have on the gene pool of its related population.
For instance, in a social insect colony, sterile workers sacrifice their own chance of reproduction in order to care for and protect the queen. Their altruism is explained by kin selection: by aiding the queen, who is closely related, they ensure that their genes persist in the gene pool. As the queen reproduces, the workers' genetic material is indirectly passed on to future generations. Hence, selection can favor traits that seem to decrease personal fitness when those traits enhance the survival and reproductive success of close relatives, effectively influencing population genetics by altering which individuals' genes are passed on.