Group selection

From EvoWiki

Group selection refers to the idea that alleles can become fixed or spread because of the benefits they bestow on groups, regardless of the fitness of individuals within that group. Group selectionist ideas have been around since Darwin mentioned it in the 'Descent of Man' as a possible mechanism of evolution of human altruism but were further elaborated by V.C. Wynne-Edwards in the 1960s.

More correctly, group selection is defined as the differential survival and reproduction of groups (Wade 1977). A response to group selection occurs when the differences among groups has a heritable basis. For group selection this means not only single locus allelic differences, but also epistatic genetic differences, differences in genetically based interactions among individuals, and even potentially cultural differences. Thus, it is simplistic to speak of group selection simply in terms of the spread of an altruistic allele.

While theoretically possible, critiques, particularly by George C. Williams (1966), John Maynard Smith (1964) and C.M. Perrins (1964) cast serious doubt on group selection as a major mechanism in evolutionary history. These responses were part of the lead up to the Williams Revolution in which gene selection theory became the prominent paradigm.

Genetic variation, the raw material of selection, is much higher between individuals than it is between groups, particularly as groups grow larger. This tendency means that alleles are likely to be held on a population-wide level, leaving nothing for group selection to select for. In addition, most phenotypes, particularly physical ones, are not highly heritable in the first place.

Additionally, generation time is much longer for groups than it is for individuals. Assuming conflicting selection pressures, individual selection will occur much faster, swamping any changes potentially favored by group selection.

Experimental work tracing from Wade (1977), and continuing to the present, has shown that group selection is far more powerful than the models would predict. Indeed in numerous experiments the response to selection was so powerful that it surprised even the experimentalists (see Goodnight and Stevens 1997). The success of these experiments led to the obvious conclusions that the models of Williams and Maynard-Smith were wrong. Wade (1978) and later Goodnight and Stevens (1997) examined this and concluded that gene interaction (epistasis) and interactions among individuals (indirect genetic effects) were contributing to the response to group selection. These complex genetic interactions could not contribute to a response to individual selection, but could contribute to a response to group selection. The early models included only very simple genetic effects, which is what had led to the erroneous rejection of group selection as an important evolutionary force.

Recently Elliot Sober and David S. Wilson have argued that the case against group selection has been overstated. They focus their argument on whether groups can have functional organization in the same way individuals do, and consequently, if groups can also be "vehicles" for selection. For example, they suggest that humans do many things to reduce reproductive differences within groups, such as passing laws against polygamy. Alternatively, groups who cooperate better may have out-reproduced those which do not. Resurrected in this way, Sober & Wilson's new group selection is usually called multilevel selection theory.

Despite a serious attempt on their part, most interested parties remain unconvinced (see, for example, Cronk, 1994; Dawkins, 1994; Dennett, 1994). Nevertheless, modified group selection approaches in many cases have been found to be far more effective than individual selection in improving crops and agricultural animals (e.g., Griffing 1977, Muir 1985, Bijma et al. 2007a, 2007b). Apparently, a modified form of group selection has become the standard approach in Europe for improving egg production in cage reared chickens.

External Links and References

• Dennett, D.C. 1994. E Pluribus Unum? Commentary on Wilson & Sober: Group Selection. Behavioural and Brain Sciences. 17 (4): 617-618.
• Dawkins, R. 1994. Burying the Vehicle. Commentary on Wilson & Sober: Group Selection. Behavioural and Brain Sciences. 17 (4): 616-617.
• Wilson, D.S. & Sober, E. 1994. Reintroducing group selection to the human behavioral sciences. Behavioral and Brain Sciences 17 (4): 585-654.

Wade, M. J. 1977. An experimental study of group selection. Evolution 31: 134-153.

Wade, M. J. 1978. A critical review of the models of group selection. Qrt. Rev. Biol. 53: 101-114.

Goodnight, C. J. and L. Stevens 1997. Experimental studies of group selection: What do they tell us about group selection in nature. American Naturalist 150: S59-S79.

Griffing, B. 1977. Selection for populations of interacting genotypes. Proceedings of the International Congress on Quantitative Genetics, August 16-21, 1976. E. Pollak, O. Kempthorne and T. B. Bailey. Ames Iowa, Iowa State University Press: 413-434.

Muir, W. M. 1985. "Relative efficiency of selection for performance of birds housed in colony cages based on production in single bird cages." Poultry Science 64: 2239-2247.

Bijma, P., W. Muir, et al. 2007. Multilevel selection 1: Quantitative genetics of inheritance and response to selection. Genetics 175: 277-288.

Bijma, P., W. Muir, et al. 2007. Multilevel selection 2: Estimating the genetic parameters determining inheritance and response to selection. Genetics 175: 289-299.

Further Reading

• Dawkins, R., 1976. The Selfish Gene. OUP.
• Wynne-Edwards, V.C., 1986. Evolution Through Group Selection. Oxford: Blackwell.