Cladistics refers to a biological classification system that involves the categorization of organisms based on shared traits. Organisms are typically grouped by how closely related they are and thus, cladistics can be used to trace ancestry back to shared common ancestors and the evolution of various characteristics. Although the classification of organisms began in the early 1900’s, cladistic analysis and specific methodology first originated in the 1960’s by Willi Hennig, referred to as “phylogenetic systematics”. This process involves creating phylogenies using morphological and molecular data to visualize evolutionary history and relationships between species.
You are watching: What is the goal of cladistics
Cladistic methodologies involve the application of various molecular, anatomical, and genetic traits of organisms. Therefore, with the advent of computational modelling and molecular techniques (e.g., polymerase chain reaction
Cladistic Character States
In the field of cladistics, specific terminology is used to describe particular characteristics, termed “character states” among groups of organisms. The following are common terms used to describe such character states (illustrated below):
Plesiomorphy refers to the ancestral traits that a taxon retains throughout evolution. Two or more taxa can share plesiomorphies but reside in different groups. When this occurs, this is termed “symplesiomorphies”. An example of a symplesiomorphy is quadrupedalism, or the ability to walk on four legs. Since this is an ancestral trait exhibited by reptiles, amphibians, and other taxa, this is a symplesiomorphy for mammals. Therefore, while symplesiomorphies can show distant evolutionary trends, it cannot be used to demonstrate more recently evolved characteristics.
Apomorphy refers to a derived state used to define specific clades. Apomorphy can be further subdivided into “autapomorphies” and “synapomorphies”. Autapomorphies refer to traits that are exhibited only by one species or group, whereas synapomorphies refer to entire clades which can be classified by the presence of a particular trait. An example of synapomophy includes the presence of digits, shared by all tetrapods. An example of an autapomorphy is the capacity of human verbal speech, which is not exhibited by other primates, and is thus, a distinguishing human trait.