"Cladistics is a method of analyzing the evolutionary relationships between groups to construct their family tree. It has been around for almost fifty years, but has really become popular in the past two decades. The principle behind it is that organisms should be classified according to their evolutionary relationships, and that the way to discover these relationships is to analyze what are called primitive and derived characters. Primitive characters are those attributes of a plant or animal which all members of the group possess. Derived characters are advanced traits which only appear in some members of the group."