Page "Molecular phylogenetics" Paragraph 2

Every living organism contains DNA, RNA, and proteins.

In general, closely related organisms have a high degree of agreement in the molecular structure of these substances, while the molecules of organisms distantly related usually show a pattern of dissimilarity.

Conserved sequences, such as mitochondrial DNA, are expected to accumulate mutations over time, and assuming a constant rate of mutation provides a molecular clock for dating divergence.

Molecular phylogeny uses such data to build a " relationship tree " that shows the probable evolution of various organisms.

Not until recent decades, however, has it been possible to isolate and identify these molecular structures.