Genetic drift specifically refers to the change of allele frequencies because of random sampling of gametes. Essentially, this induces genetic bias for particular alleles and can lead to speciation events simply by the chance event of certain gametes producing offspring rather than others.

Changes in mutation frequencies, random mating, and natural selection may lead to changes in allele frequencies, but they are not necessarily the cause of genetic drift.

Genetic drift occurs when a gene's frequency is changed in a population due to pure chance. Consider a rock rolling down a hill and crushing all flowers that have white petals. The population will now have only red petals because the white ones were destroyed. Were the red petal flowers more suited to their environment? No, it just so happened that all of the white were removed from the gene pool. This shows that evolution can occur due to random chance as well as natural selection, and both forces can have an impact on a population.