Concerted evolution is the phenomenon where paralogous genes within one species are more closely related to one another than to members of the same gene family in closely related species. It is possible that this might occur even if the gene duplication event preceded the speciation event. High sequence similarity between paralogs may be maintained by homologous recombination events that lead to gene conversion, effectively copying some sequence from one and overwriting the homologous region in the other. Another possible hypothesis that has yet to be disproved is that rapid waves of gene duplication are responsible for the apparently "concerted" homogeneity of tandem and unlinked repeats seen in concerted evolution.