4.14—Classification and taxonomy

Taxonomy organises organisms into nested groups using similarities and differences in phenotype and genotype. The species concept is the base: members can usually produce fertile offspring; higher ranks group progressively broader relationships.

Molecular evidence can overturn a classification based only on appearance. Comparing DNA, RNA or proteins supports molecular phylogeny: greater sequence similarity generally indicates a more recent common ancestor.

The three-domain system separates Archaea, Bacteria and Eukarya because molecular evidence showed that “prokaryote” was not one evolutionary group. A new grouping should be critically evaluated by the scientific community.

Classification is a model of relationship, not a fixed list of visual labels. A similar phenotype can evolve independently, and a binomial name is not evidence that two organisms are the same species.