Data A systematist gathers data. Any scientific approach to classification needs evidence and systematics is that branch of science that provides the data and evidence needed to justify decissions taken later. Organisms are examined from as many points of view as possible.
All branches of science contribute.
Everyone has something to contribute. Thousands of facts about each creature studied are assembled and amassed into data banks. A popular item of data these days are DNA electrophoretic patterns generated by cutting up the hereditary apparatus of an organism with special enzymes and then separating the fragments by length. These patterns can give a lot of data about the present and past state of the organims carrying them, and strong similarities in DNA patterns argue for a close relationship. Such a close resemblence between the DNA of the two species suggests that humans and chimpanzees should occupy either the same, or very closely related groups in any classification scheme.