 W. D. Hamilton proposed kin selection as a resolution to the altruism puzzle (Hamilton 1964). If the population of ground squirrels above were related, then the genes associated with alarm calling could propagate in the group even if the altruistic ground squirrels were killed more often because their kin who shared the genes survived. G. C. Williams and Richard Dawkins subsequently generalized Hamilton’s observation, arguing that all of natural selection could be understood as operating at the genetic level (Williams 1966; Dawkins 1976). On this “gene’s-eye view of evolution”, natural selection targets genes (the “replicators” in Dawkins’ language), while organisms are the “vehicles” (or “interactors”) that carry around the genes and interact with the environment (entry:  replication and reproduction).