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. 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. It contrasted the popular hypothesis that evolution of such social behavior was based on mutual benefits to the population.

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