Abstract: The widely accepted viewpoint that feralization is the reverse of domestication requires that the feralization process be restricted to populations of animals and, therefore, cannot occur in individuals. An alternative, ontogenetic approach is presented in which feralization is defined as the process by which individual domestic animals either become desocialized from humans, or never become socialized, and thus behave as untamed, non-domestic animals. Feralization will vary among species and, intraspecifically, will depend upon an individual's age and history of socialization to humans. Because feralization is not equated with morphological change resulting from evolutionary processes, species formation is not an accurate indicator of feral condition.