Evolution can be thought of as a two-step process. First, genetic variation arises. Genetic variation has its origin in the processes of mutation, which produces new alleles, and recombination, which shuffles alleles into new combinations. Both of these processes are random and produce genetic variation continually, regardless of evolution’s requirement for it. The second step in the process of evolution is change in the frequencies of genetic variants. The various evolutionary forces discussed in the previous section cause some alleles in the gene pool to increase in frequency and other alleles to decrease in frequency. This shift in the composition of the gene pool constitutes evolutionary change.