  group selection refers to one mechanism of evolution in which natural selection acts at the level of the group instead of at the more conventional level of the individual. many species have a social structure in which individuals form groups and interaction among members within each group is much more frequent than interaction of individuals across groups. when selection for a biological trait, often altruism, in such populations depends on the difference between groups rather than individual differences within a group, it is described as group selection in evolutionary biology. group selection in this sense is often called multi-level selection, because it posits social organization with a complexity above simple interactions of individuals. group selection theories argue that a behavior may spread in a population because of the benefits they bestow on groups even though they cause the individuals who exhibit this behavior to sacrifice fitness by aiding the group. group selection was used as a popular explanation for adaptations, especially by v. c. wynne-edwards.wynne-edwards, v.c. (1962). animal dispersion in relation to social behaviour. edinburgh: oliver & boyd.wynne-edwards, v. c. (1986) evolution through group selection, blackwell. isbn 0-632-01541-1 for several decades, however, critiques, particularly by george c. williams,williams, g.c. (1972) adaptation and natural selection: a critique of some current evolutionary thought. princeton university press.isbn 0-691-02357-3 john maynard smith and c.m. perrins (1964), historically cast serious doubt on group selection as a major mechanism of evolution. however, some scientists have pursued the idea over the last few decades, and group selection models have seen a resurgence since the mid-1990s with increasing popularity.koeslag, j.h. (1997). sex, the prisoner's dilemma game, and the evolutionary inevitability of cooperation. j. theor. biol. 189, 53--61koeslag, j.h. (2003). evolution of cooperation: cooperation defeats defection in the cornfield model. j. theor. biol. 224, 399-410{{cite journal|last=
Population_genetics Selection