Phylogenetic systematics is a method of classification based on the evolutionary history of organisms, dividing organisms into meaningful groups and subgroups. It was developed by Willi Hennig , an entomologist, in 1950, but was not well accepted until decades later. Evolution results in modifications of characteristics over time. A cladogram is a branching diagram that depicts species divergence from common ancestors. They show the distribution and origins of shared characteristics.
Cladograms are testable hypotheses of phylogenetic relationships.
The members of a monophyletic group are closely related to each other. A monophyletic group is called a clade. An example of a monophyletic group is mammals. A paraphyletic group consists of a common ancestor and some, but not all, of its descendants. These are incomplete groups based primarily on physical characteristics rather than directly on evolutionary relationships.