Genetic Drift
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In addition to the process of natural selection, naturally occurring catastrophic and human induced events as well as random environmental changes can result in alteration in the gene pools. Small populations are especially sensitive to these forces. A diverse gene pool is vital for the survival of species because environmental conditions change. Mutations in DNA and recombination during meiosis are sources of variation. Human-directed processes also result in new genes and combinations of alleles that confer new phenotype. Mathematical approaches are used to calculate changes in allele frequency, providing evidence for the occurrence of evolution in a population.