Taxa in the context of Carl Linnaeus

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 (synonyms: phylogenetic trees, phylogenies). Phylogenies have two components: branching order (showing group relationships, graphically represented in cladograms) and branch length (showing amount of evolution). Phylogenetic trees of species and higher taxa are used to study the evolution of traits (e.g., anatomical or molecular characteristics) and the distribution of organisms (biogeography). Systematics, in other words, is used to understand the evolutionary history of life on Earth.

The word systematics is derived from the Latin word of Ancient Greek origin systema, which means systematic arrangement of organisms. Carl Linnaeus used 'Systema Naturae' as the title of his book.

Injury is physiological damage to the living tissue of any organism, whether in humans, in other animals, or in plants.

Injuries can be caused in many ways, including mechanically with penetration by sharp objects such as teeth or with blunt objects, by heat or cold, or by venoms and biotoxins. Injury prompts an inflammatory response in many taxa of animals; this prompts wound healing. In both plants and animals, substances are often released to help to occlude the wound, limiting loss of fluids and the entry of pathogens such as bacteria. Many organisms secrete antimicrobial chemicals which limit wound infection; in addition, animals have a variety of immune responses for the same purpose. Both plants and animals have regrowth mechanisms which may result in complete or partial healing over the injury. Cells too can repair damage to a certain degree.

In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each other, further blurring any distinctions. Terms that are sometimes used synonymously but have more precise meanings are cryptic species for two or more species hidden under one species name, sibling species for two (or more) species that are each other's closest relative, and species flock for a group of closely related species that live in the same habitat. As informal taxonomic ranks, species group, species aggregate, macrospecies, and superspecies are also in use.

Two or more taxa that were once considered conspecific (of the same species) may later be subdivided into infraspecific taxa (taxa within a species, such as plant varieties), which may be a complex ranking but it is not a species complex. In most cases, a species complex is a monophyletic group of species with a common ancestor, but there are exceptions. It may represent an early stage after speciation in which the species were separated for a long time period without evolving morphological differences. Hybrid speciation can be a component in the evolution of a species complex.

A phenotypic trait, simply trait, or character state is a distinct variant of a phenotypic characteristic of an organism; it may be either inherited or determined environmentally, but typically occurs as a combination of the two. For example, having eye color is a character of an organism, while blue, brown and hazel versions of eye color are traits. The term trait is generally used in genetics, often to describe the phenotypic expression of different combinations of alleles in different individual organisms within a single population, such as the famous purple vs. white flower coloration in Gregor Mendel's pea plants. By contrast, in systematics, the term character state is employed to describe features that represent fixed diagnostic differences among taxa, such as the absence of tails in great apes, relative to other primate groups.

Scientific racism, sometimes termed biological racism, is the pseudoscientific belief that the human species is divided into biologically distinct taxa called "races", and that empirical evidence exists to support or justify racial discrimination, racial inferiority, or racial superiority. Before the mid-20th century, scientific racism was accepted throughout the scientific community, but it is no longer considered scientific. The division of humankind into biologically separate groups, along with the assignment of particular physical and mental characteristics to these groups through constructing and applying corresponding explanatory models, is referred to as racialism, racial realism, race realism, or race science by those who support these ideas. Modern scientific consensus rejects this view as being irreconcilable with modern genetic research.

Scientific racism misapplies, misconstrues, or distorts anthropology (notably physical anthropology), craniometry, evolutionary biology, and other disciplines or pseudo-disciplines through proposing anthropological typologies to classify human populations into physically discrete human races, some of which may be asserted to be superior or inferior to others.

Freshwater bivalves are molluscs of the order Bivalvia that inhabit freshwater ecosystems. They are one of the two main groups of freshwater molluscs, along with freshwater snails.

The majority of bivalve molluscs are saltwater species that live in the marine habitats, but a number of families have evolved to live in fresh water (and in some cases, also in brackish water). These belong to two different evolutionary lineages, i.e. freshwater mussels and freshwater clams, and the two groups are not closely related. Freshwater bivalves have a simple morphology that varies among taxa, and are distributed around most regions of the world.

Injury in animals is damage to the body caused by wounding, change in pressure, heat or cold, chemical substances, venoms and biotoxins. Injury prompts an inflammatory response in many taxa of animals; this prompts wound healing, which may be rapid, as in the Cnidaria.

In biology, a tribe is a taxonomic rank above genus, but below family and subfamily. It is sometimes subdivided into subtribes. By convention, all taxa ranked above species are capitalized, including both tribe and subtribe.

In zoology, the standard ending for the name of a zoological tribe is "-ini". Examples include the tribes Caprini (goat-antelopes), Hominini (hominins), Bombini (bumblebees), and Thunnini (tunas). The tribe Hominini is divided into subtribes by some scientists; subtribe Hominina then comprises "humans". The standard ending for the name of a zoological subtribe is "-ina".

The dingo (either included in the species Canis familiaris, or considered one of the following independent taxa: Canis familiaris dingo, Canis dingo, or Canis lupus dingo) is an ancient (basal) lineage of dog found in Australia. Its taxonomic classification is debated as indicated by the variety of scientific names presently applied in different publications. It is variously considered a form of domestic dog not warranting recognition as a subspecies, a subspecies of dog or wolf, or a full species in its own right.

The dingo is a medium-sized canine that possesses a lean, hardy body adapted for speed, agility, and stamina. The dingo's three main coat colourations are light ginger or tan, black and tan, or creamy white. The skull is wedge-shaped and appears large in proportion to the body. The dingo is closely related to the New Guinea singing dog: their lineage split early from the lineage that led to today's domestic dogs, and can be traced back through Maritime Southeast Asia to Asia. The oldest remains of dingoes discovered in Australia are around 3,500 years old.

In biology, homology is similarity in anatomical structures or genes between organisms of different taxa due to shared ancestry, regardless of current functional differences. Evolutionary biology explains homologous structures as retained heredity from a common ancestor after having been subjected to adaptive modifications for different purposes as the result of natural selection.

The term was first applied to biology in a non-evolutionary context by the anatomist Richard Owen in 1843. Homology was later explained by Charles Darwin's theory of evolution in 1859, but had been observed before this from Aristotle's biology onwards, and it was explicitly analysed by Pierre Belon in 1555. A common example of homologous structures is the forelimbs of vertebrates, where the wings of bats and birds, the arms of primates, the front flippers of whales, and the forelegs of four-legged vertebrates like horses and crocodilians are all derived from the same ancestral tetrapod structure.

Aquilegia, commonly known as columbines, is a genus of perennial flowering plants in the family Ranunculaceae (buttercups). The genus includes between 80 and 400 taxa (described species and subspecies) with natural ranges across the Northern Hemisphere. Natural and introduced populations of Aquilegia exist on all continents but Antarctica. Known for their high physical variability and ease of hybridization, columbines are popular garden plants and have been used to create many cultivated varieties.

Aquilegia typically possess stiff stems and leaves that divide into multiple leaflets. Columbines often have colorful flowers with five sepals and five petals. The petals generally feature nectar spurs which differ in lengths between species. In North America, morphological variations in spurs evolved to suit different pollinators. Some species and varieties of columbines are naturally spurless. In cultivation, varieties bearing significantly altered physical traits such as double flowering are prevalent.

Computational phylogenetics, phylogeny inference, or phylogenetic inference focuses on computational and optimization algorithms, heuristics, and approaches involved in phylogenetic analyses. The goal is to find a phylogenetic tree representing optimal evolutionary ancestry between a set of genes, species, or taxa. Maximum likelihood, parsimony, Bayesian, and minimum evolution are typical optimality criteria used to assess how well a phylogenetic tree topology describes the sequence data. Nearest Neighbour Interchange (NNI), Subtree Prune and Regraft (SPR), and Tree Bisection and Reconnection (TBR), known as tree rearrangements, are deterministic algorithms to search for optimal or the best phylogenetic tree. The space and the landscape of searching for the optimal phylogenetic tree is known as phylogeny search space.

Maximum Likelihood (also likelihood) optimality criterion is the process of finding the tree topology along with its branch lengths that provides the highest probability observing the sequence data, while parsimony optimality criterion is the fewest number of state-evolutionary changes required for a phylogenetic tree to explain the sequence data.