Kin selection is explainable at the gene level. From this perspective, altruistic behavior is not altruistic but selfish. An alternative explanation for some altruistic behavior, not mentioned by Ridley, is that some altruistic behavior may result from genetic or developmental constraints on instincts. The issue of whether group selection ever produces adaptations for the benefit of groups has been controversial, though most biologists now think it is only a weak force in evolution. The distinction is that kin selection is understood to involve selection which benefits individuals carrying particular genes, not selection for the groups themselves.
Selection based individual advantage is presumed always to maximize reproductive capacity.
Some species do exhibit restrained reproductive capacity. At least some cases can be explained by individual advantage. To assure resources for reproduction, individuals defend territories. Within each territory, resources are limited. Individuals maximize their own individual reproductive potential by matching reproductive effort to available resources.