Effective population size

Effective population size is a population genetic parameter that is used to assess the impact of genetic drift on allele frequencies within a finite population. It is the number of breeding individuals within an idealized (Wright–Fisher) population. Within human populations, effective population size is generally smaller than the census size of adults. Effective population size is affected by a number of demographic factors including fluctuations in population size, variability in the number of offspring, and unequal sex proportions. The long‐term effective population size for humans, beginning in the Pleistocene, is estimated to include only 1,000–10,000 individuals.