NOTE 19CC: Maynard and Haigh (1974) were originally motivated by the need to explain why random drift seems to occur even in very large populations, so that genetic diversity is not extremely high. This point of view has been extended recently by Gillespie (2000a,b). Gillespie terms the cumulative effect of hitch-hiking “genetic draft,” in contrast to “random drift.” Although the rate of increase of variance in allele frequency is the same, for the same effective population size, the two processes are otherwise very different, and can in principle be distinguished by comparing patterns of variation (see pp. 536–538).