The two different sources of variation is mutation and recombination. Mutations are changes in the DNA where a single change can have large effect in evolution when accumulated. It can stimulate rapid evolution of populations by providing new genetic variation on which natural selection, genetic drift, or gene flow can act.
Meanwhile, DNA recombination involves the exchange of genetic material either between multiple chromosomes or between different regions of the same chromosome through sexual reproduction where genetic shuffling occurs. This shuffling is important for evolution because it can introduce new combinations of genes in every generation.