 By comparing the homology between different species ' genomes , it is possible to calculate the evolutionary distance between them and when they may have diverged . Genetic comparisons are generally considered a more accurate method of characterizing the relatedness between species than the comparison of phenotypic characteristics . The evolutionary distances between species can be used to form evolutionary trees ; these trees represent the common descent and divergence of species over time , although they do not show the transfer of genetic material between unrelated species ( known as horizontal gene transfer and most common in bacteria ) . 
