The variation in allele frequencies between several isolated populations can be due to genetic drift - VCE - SSCE Biology - Question 25 - 2003 - Paper 1

Genetic drift is a mechanism of evolution that refers to random changes in allele frequencies in a population, which can have significant effects especially in small populations. When a population is drastically reduced in size, for example due to a natural disaster or human activity, the genetic variation can be greatly affected. This scenario can lead to increased susceptibility to genetic drift as the remaining individuals may not represent the original gene pool. Thus, genetic drift is likely to be observed when a population is reduced to a few individuals.