Selfish herd theory

The selfish herd theory states that individuals within a population attempt to reduce their predation risk by putting other conspecifics between themselves and predators.^[1] A key element in the theory is the domain of danger, the area of ground in which every point is nearer to a particular individual than to any other individual. Such antipredator behavior inevitably results in aggregations. The theory was proposed by W. D. Hamilton in 1971 to explain the gregarious behavior of a variety of animals.^[1] It contrasted the popular hypothesis that evolution of such social behavior was based on mutual benefits to the population.^[1]

The basic principle governing selfish herd theory is that in aggregations, predation risk is greatest on the periphery and decreases toward the center.^[1] More dominant animals within the population are proposed to obtain low-risk central positions, whereas subordinate animals are forced into higher risk positions.^[2] The hypothesis has been used to explain why populations at higher predation risk often form larger, more compact groups.^[3] It may also explain why these aggregations are often sorted by phenotypic characteristics such as strength.^[4]