Every living organism contains DNA, RNA, and proteins.
Closely related organisms generally 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.
Molecular phylogeny uses such data to build a "relationship tree" that shows the probable evolution of various organisms.
Molecular phylogenetics attempts to determine the rates and patterns of change occurring in DNA and proteins and to reconstruct the evolutionary history of genes and organisms.
Two general approaches may be taken to obtain this information.
In the first approach, scientists use DNA to study the evolution of an organism.
In the second approach, different organisms are used to study the evolution of DNA.
Whatever the approach, the general goal is to infer process from pattern: the processes of organismal evolution deduced from patterns of DNA variation and processes of molecular evolution inferred from the patterns of variations in the DNA itself.
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