Cladistics is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived characteristics (synapomorphies) that are not present in more distant groups and ancestors. However, from an empirical perspective, common ancestors are inferences based on a cladistic hypothesis of relationships of taxa whose character states can be observed. Theoretically, a last common ancestor and all its descendants constitute a (minimal) clade. Importantly, all descendants stay in their overarching ancestral clade. For example, if the terms worms or fishes were used within a strict cladistic framework, these terms would include humans. Many of these terms are normally used paraphyletically, outside of cladistics, e.g. as a 'grade', which are fruitless to precisely delineate, especially when including extinct species. Radiation results in the generation of new subclades by bifurcation, but in practice sexual hybridization may blur very closely related groupings.
In biological phylogenetics, a clade, also known as a monophyletic group or natural group, is a grouping of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. In the taxonomical literature, sometimes the Latin form cladus is used rather than the English form.
In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade — that is, a grouping of taxa which meets these criteria:
- the grouping contains its own most recent common ancestor, i.e. excludes non-descendants of that common ancestor
- the grouping contains all the descendants of that common ancestor, without exception
In biology, phylogenetics is the study of the evolutionary history and relationships among or within groups of organisms. These relationships are determined by phylogenetic inference methods that focus on observed heritable traits, such as DNA sequences, protein amino acid sequences, or morphology. The result of such an analysis is a phylogenetic tree—a diagram containing a hypothesis of relationships that reflects the evolutionary history of a group of organisms.
In biology, phenetics, also known as taximetrics, is an attempt to classify organisms based on overall similarity, usually in morphology or other observable traits, regardless of their phylogeny or evolutionary relation. It is closely related to numerical taxonomy which is concerned with the use of numerical methods for taxonomic classification. Many people contributed to the development of phenetics, but the most influential were Peter Sneath and Robert R. Sokal. Their books are still primary references for this sub-discipline, although now out of print.
Biological systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees. Phylogenies have two components: branching order and branch length. Phylogenetic trees of species and higher taxa are used to study the evolution of traits and the distribution of organisms (biogeography). Systematics, in other words, is used to understand the evolutionary history of life on Earth.
Emil Hans Willi Hennig was a German biologist and zoologist who is considered the founder of phylogenetic systematics, otherwise known as cladistics. In 1945 as a prisoner of war, Hennig began work on his theory of cladistics, which he published in German in 1950, with a substantially revised English translation published in 1966. With his works on evolution and systematics he revolutionised the view of the natural order of beings. As a taxonomist, he specialised in dipterans.
Evolutionary taxonomy, evolutionary systematics or Darwinian classification is a branch of biological classification that seeks to classify organisms using a combination of phylogenetic relationship, progenitor-descendant relationship, and degree of evolutionary change. This type of taxonomy may consider whole taxa rather than single species, so that groups of species can be inferred as giving rise to new groups. The concept found its most well-known form in the modern evolutionary synthesis of the early 1940s.
In phylogenetics, an apomorphy is a novel character or character state that has evolved from its ancestral form. A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have evolved in their most recent common ancestor. In cladistics, synapomorphy implies homology.
Norman Ira Platnick was an American biological systematist and arachnologist. At the time of his death, he was a professor emeritus of the Richard Gilder Graduate School and Peter J. Solomon Family Curator Emeritus of the invertebrate zoology department of the American Museum of Natural History. A 1973 Ph.D. recipient at Harvard University, Platnick described over 1,800 species of spiders from around the world, making him the second most prolific spider taxonomist in history, behind only Eugène Simon. Until 2014 he was also the maintainer of the World Spider Catalog, a website formerly hosted by the AMNH which tracks the arachnology literature, and attempts to maintain a comprehensive list, sorted taxonomically, of every species of spider which has been formally described. In 2007 he received the International Society of Arachnology's Bonnet award, named for Pierre Bonnet, in recognition of his work on the catalog.
Adolf Naef was a Swiss zoologist and palaeontologist who worked on cephalopods and systematics. Although he struggled with academic politics throughout his career and difficult conditions during World War I and II, his work had lasting influences on the fields of phylogenetics, morphology, and embryology.
Phylogenetic nomenclature is a method of nomenclature for taxa in biology that uses phylogenetic definitions for taxon names as explained below. This contrasts with the traditional approach, in which taxon names are defined by a type, which can be a specimen or a taxon of lower rank, and a description in words. Phylogenetic nomenclature is currently regulated by the International Code of Phylogenetic Nomenclature (PhyloCode).
Coleorrhyncha or Peloridiomorpha, also known as moss bugs or beetle bugs, are a suborder of Hemiptera and represent an ancient lineage of moss-feeding insects. They show some similarities to the Heteroptera but have been considered distinct. It has a single extant family, the Peloridiidae. They are 2 to 5 millimetres in length, and feed on moss and liverworts. They have wings in some species which are reduced in others but all species are flightless and live in damp moss habitats and are associated with the distribution of Nothofagus trees in Australia, New Zealand, New Caledonia, and South America, which all were formerly part of the supercontinent Gondwana.
The Willi Hennig Society "was founded in 1980 with the expressed purpose of promoting the field of phylogenetic systematics." The society is represented by phylogenetic systematists managing and publishing in the peer-reviewed journal titled Cladistics. The society is named after Willi Hennig, a German systematic entomologist who developed the modern methods and philosophical approach to systematics in the 1940s and 1950s. The society is also involved in reconstructing the tree of life. The current president, Prof. Dr. Stefan Richter of Universitat Rostock, was elected in 2022, succeeding Prof. Dr. Christiane Weirauch.
Arnold G. Kluge is professor emeritus of zoology and curator emeritus of amphibians and reptiles at the University of Michigan, Museum of Zoology. Kluge authored over 140 journal articles. He served as past president of the Willi Hennig Society and as editor-in-chief of its journal Cladistics. He served at the University of Michigan from 1965 until his retirement in 2003.
The Society of Systematic Biologists (SSB) started as the Society of Systematic Zoology in 1947. A temporary constitution was adopted at the first meeting on 28 December 1947. The updated "biologists" organization become incorporated on August 9, 1971.
The Systematics Association is a charitable organisation based in the UK founded in 1937 for the promotion of the study of systematics and taxonomy. It publishes research, organises conferences, and provides competitive research funds for systematics research.
Transformed cladistics, also known as pattern cladistics is an epistemological approach to the cladistic method of phylogenetic inference and classification that makes no a priori assumptions about common ancestry. It was advocated by Norman Platnick, Colin Patterson, Ronald Brady and others in the 1980s, but has few modern proponents. The book, Foundations of Systematics and Biogeography by David Williams and Malte Ebach provides a thoughtful history of the origins of this point of view.
Ole Engel Heie was a Danish biology professor and entomologist who specialized in the Aphidomorpha. He published a highly influential six-part monograph on the aphids as part of the Fauna Entomologica Scandinavica published from 1980 - 1995.
Delbert Dwight Davis, was an American comparative anatomist and curator of zoology at the Chicago Natural History Museum.
