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.