Caste Development Research Articles

Group Selection and Its Significance for Ecology

Selection can be said to operate at the group level and deserves to be called group selection, when it affects two or more members of a lineage group as a unit. Just above the level of the individual we can delimit various of these lineage groups: a set of sibs, parents, and their offspring, a close-knit tribe of families related by at least the degree of third cousin, and so on. If selection operates on any of the groups as a unit, the process is referred to as kin selection. At a higher level, an entire breeding population may be the unit, so that populations (i.e., demes) possessing different genotypes are diminished or extinguished differentially, in which case we speak of interdemic (or interpopulation) selection. hierarchy of ascending levels of selection is visualized in Figure 1. concept of group selection was introduced by Darwin in The Origin of Species to account for the evolution of sterile castes in social insects. term intergroup selection, in the sense of interdemic selection defined here, was used by Sewall Wright in 1945. Essentially the same expression (Gruppenauslese), was used independently and with the same meaning by Olavi Kalela (1954, 1957), while the phrase kin selection was coined by J. Maynard Smith (1964). classification adopted here is approximately that recommended by J. L. Brown (1966). Selection can also operate at the level of species or entire clusters of related species. process, well known to paleontologists and biogeographers, is responsible for the familiar patterns of dynastic succession of major groups such as ammonites, sharks, graptolites, and dinosaurs through geologic time (Simpson 1953, P. J. Darlington 1971). It is even possible to conceive of the differential extinction of entire ecosystems, involving all trophic levels (Dunbar 1960). However, selection at these highest levels is not likely to be important in the evolution of altruism, for the following simple reason. In order to counteract individual