The neutral theory in an infinite population

Selective substitutions at one locus induce stochastic dynamics at a linked neutral locus that resemble genetic drift even when the population size is infinite. This new stochastic force, which is called genetic draft, causes genetic variation at the neutral locus to decrease with population size an d the rate of deleterious substitution to increase with population size. Th e fact that heterozygosities in natural populations are only weakly depende nt on population size suggests that genetic draft may be a much more import ant stochastic force than genetic drift in natural populations. Some of the mathematical properties of genetic draft are explored. (C) 2000 Elsevier S cience B.V. All rights reserved.