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Hard and Soft Selection Revisited

Bruce Wallace
Evolution
Vol. 29, No. 3 (Sep., 1975), pp. 465-473
DOI: 10.2307/2407259
Stable URL: http://www.jstor.org/stable/2407259
Page Count: 9
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Hard and Soft Selection Revisited
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Abstract

The concepts of hard and soft selection (Wallace, 1968, 1970) have been reviewed. Juvenile mortality as well as rigid and flexible selection (Dobzhansky, 1962, 1970) have been shown to be unrelated to the ideas illustrated by the published examples of soft selection. The following definitions are suggested: hard selection is both density and frequency independent; soft selection is both density and frequency dependent. Under this classification, selection that is now referred to as 'density-dependent' would be frequency-independent while that known as 'frequency-dependent' would be density-independent (Fig. 1). An analysis of an ecological model presented by Clarke (1973a, b) reveals that under certain conditions α-, k-, and w-selection all qualify as soft selection. Clarke's α-selection is always soft; his k-selection may at times be density-dependent only.

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