Molecular systematics is the use of molecular genetics to study the evolution of relationships among individuals and species. The goal of systematic studies is to provide insight into the history of groups of organisms and the evolutionary processes that create diversity among species. Molecular biology has revolutionized the field of systematics. DNA evolves by mutations being incorporated in the DNA and fixed in populations. This will lead to divergence of DNA sequences in different species. Although diverged, we can refer to two DNA sequences as homologous (just as we would for any morphological trait such as forelimbs. Nicely demonstrates descent with modification as a definition of evolution. For this reason, DNA should be an excellent tool for inferring phylogenies: large number of homologous characters that should be less subject to convergent evolution than other characters that might lead to a confusion of grade and clade. In general, molecular systematics provides a powerful statistical framework for hypothesis testing and the estimation of evolutionary processes, including the estimation of divergence times among taxa. The field of molecular systematics has experienced a revolution in recent years, and, although there are still methodological problems and pitfalls, it has become an essential tool for the study of evolutionary patterns and processes at different levels of biological organization.
