21.5 Migration, Mutation, Genetic Drift, and Non-Random Mating

Selection is evolution’s major driving force, enriching each new generation for the mutations that best fit organisms to their environments. However, as we have seen, it is not the only evolutionary mechanism. There are other mechanisms that can cause allele and genotype frequencies to change. These are migration, mutation, genetic drift, and non-random mating. Like natural selection, these mechanisms can cause allele frequencies to change. Unlike natural selection, they do not lead to adaptations.