View source for Effective population size

'''Effective population size''' ($N_e$) is a concept in [[population genetics]] that measures the size of an idealized population that would experience the same magnitude of [[genetic drift]] as the actual population under study. The actual population may be larger than $N_e$ due to factors that reduce genetic diversity: unequal sex ratios, variation in family size, population bottlenecks, and non-random mating.

The effective population size determines the balance between [[natural selection]] and [[genetic drift]]. When $N_e$ is large, selection dominates and advantageous alleles spread reliably. When $N_e$ is small, drift can overpower selection and drive alleles to fixation regardless of their fitness effects. This is why [[balancing selection]] can maintain polymorphisms in large populations but may fail in small ones.

The concept was developed by [[Sewall Wright]] and remains central to understanding how population structure shapes evolutionary outcomes. In conservation biology, $N_e$ is the key parameter for predicting the viability of endangered populations; in evolutionary theory, it sets the threshold for when selection becomes effective.

[[Category:Population Genetics]] [[Category:Evolutionary Biology]]