In ethology and evolutionary biology, group living is defined as individuals of the same species (conspecifics), maintaining spatial proximity with one another over time with mechanisms of social attraction. Solitary life in animals is considered to be the ancestral state of living; and group living has thus evolved independently in many species of animals. Therefore, species that form groups through social interaction will result in a group of individuals that gain an evolutionary advantage, such as increased protection against predators, access to potential mates, increased foraging efficiency and the access to social information. Important aspects of group living include the frequency and type of social interactions (egoistic, cooperative, altruistic, revengeful) between individuals of a group (social life), the group size, and the organization of group members in the group. Terminology of animal groups also varies among different taxonomic groups. Groups of sheep are termed herds, whilst groups of birds are referred to as colonies, or flocks. Most studies on group living focus strictly on groups comprising a single species. However, many mixed-species groups commonly occur in nature. Examples of mixed-species groups include wildebeests forming groups with zebras, and different species of birds that form large foraging flocks. Group living may sometimes be confused with collective animal behavior. Collective animal behavior is the study of how the interactions between individuals of a group give rise to group level patterns and how these patterns have evolved. Examples include the marching of locusts and flocks of migrating birds. Group living however focuses on the long-term social interactions between individuals of a group and how animals have evolved from solitary living. Definition of group living It is extremely difficult to distinguish between solitary living and group living. Distinctions between the two are relatively artificial. This is because many species of animals who spend a majority of their life alone, at some point in their life, will join a group or engage in social behavior. Some examples of this happens during mating, parental care of their offspring, or even aggregations of conspecifics to an area to exploit resources of food or shelter. Therefore, multiple definitions of group living have been proposed. Differences in group living definitions vary dependent on the frequency and type of social interactions that members of a group display and the level of coordination and cohesion of group members. For example, Wilson (2000) defines a group as “any set of organisms, belonging