The Coalescent Time in the Presence of Background Fertility Selection

Selection ultimately entails differential reproductive success over several generations. This can be measured as a correlation of the number of progeny an individual has with the number of progeny its parent had. This correlation could have a genetic or a cultural basis. The effect of such a correlation is to multiply the single generation sampling variance (Vδp) in the diffusion approximation for fixation time by (1−b)+b×(1+r)/(1−r), where b×rn is the correlation between the number of progeny of an individual and its ancestor n generations ago (e.g., b is the heritability and br is the resultant parent–offspring progeny number correlation if the progeny number is genetically determined). This results in a reduction of the fixation or coalescent time by division by this factor. Sex differences in this correlation have been observed, and this provides an explanation for the difference of coalescent times of y-chromosomes and mitochondria