The correct answer is taxonomy,
Taxonomy is a branch of biology that aims to to sort living thing into categories. In its early years, taxonomy was solely based on structural comparisons, mostly the anatomical similarities and differences between the organisms. However, with the discovery of the physiological processes and the genetic structures of organisms, the previous taxonomic knowledge was revised and changed in the light of the new scientific finds. Nowadays, taxonomy is primarily based on genetic similarities between the organisms.
