Is stranger/separation anxiety in infancy the onset of territoriality and in-group favoritism?

Humans instinctively tend to favor members of their own group more than members of other groups. The evolution of this in-group preference in connection with the basic instinct of territoriality is emphasized. By reinterpreting stranger/separation anxiety in infancy as the onset of territoriality and the in-group favoritism, we bring the seemingly distinct psychological behaviors into a unified framework that also sheds light on the evolutionary origin of the correlated traits. This interpretation predicts the existence of an evolved unified neural circuitry, starting around six months of age that is responsible for the exhibition of coevolved behaviors of stranger/separation anxiety, territoriality, and in-group favoritism throughout a human’s life.