Center for Invertebrate Biology


Allopatric Speciation: The development of new species due to the complete geographic and genetic isolation of populations from the original population.

Analogy: Functional or structural similarity of structures that perform a similar function but are not related through inheritance from a common ancestor. (See convergence).

Autapomorphy: A unique character found only within a particular taxon. These characters do not provide phylogenetic information but can be used to distinguish the taxonomic group.

Biological Species Concept (Isolation Species Concept): A species is a group of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups.(See Species Concepts)

Convergence: Structural similarity involving the evolution of similar traits in organisms that do not share a common ancestor but are developing similar structures to solve similar evolutionary problems. Examples include: Shark and Dolphin flippers, Bird and Bat wings. (See Analogy)

Evolution: The process by which populations change over time and new species develop. Originally defined by Darwin and Wallace as "descent with modification."

Evolutionary Species Concept (Phylogenetic Species Concept): A species consists of a population or group of populations that share a common evolutionary fate through time. (See Species Concepts)

Homology: Structural similarity of traits due to the inheritance of the trait from a common ancestor.

Monophyletic: A taxonomic group of organisms that contains the most recent ancestor of the group and all of its descendants.

Natural selection: The "natural" process that selects those individuals that are better fit to survive in the environment due to inherent differences in morphology as related to their genetic makeup. "Also known as the survival of the fittest."

Parapatric Speciation: Speciation that occurs at the edge of the range of the original population without geographic isolation.

Paraphyletic: A taxonomic group of organisms that contains the most recent ancestor of the group but not all of its descendants.

Phylogeny: 1. The evolutionary history of a group of organisms showing the evolutionary relationships of ancestors and descendants. 2. The evolutionary 'lineage' of a group of organisms.

Polyphyletic: A taxonomic group of organisms that does not contain the most recent ancestor of the group and can contain multiple lineages of organisms.

Population: A group of organisms composed of individuals of the same species living within a specific geographic region.

Speciation: The evolutionary process that results in the development of new species from an original population or species.

Species Concepts: There are several current scientific definitions of a species, all with some slight differences and with differing applications.

Sympatric Speciation: The establishment of a new species within the range of the original population due to mutations or other changes that result in reproductive isolation.

Symplesiomorphy: A shared ancestral character that is common to a taxonomic group of organisms and does not provide information about phylogenetic relationships within the group.

Synapomorphy: A shared derived character. An evolutionarily derived character that is found in the ancestor and its descendants that can be used to reconstruct phylogenetic relationships.

Systematics: The science of the classification of organisms, including the naming and maintaining of specimens in herbaria and museums, reconstructing the phylogenetic(evolutionary) relationships of organisms and maintaining records of all known organisms.

Taxon: (Taxon singular, Taxa plural) A group of organisms that are related through shared ancestry.

Total Evidence Hypothesis: 1. The hypothesis that proposes that all available types of characters no matter how they were generated should be used in combination to reconstruct the phylogenetic relationships of organisms.
2. Species are a mosaic of both morphological and genetic characteristics. All characters describing a species have been simultaneously acted upon by natural selection and represent the evolutionary history (phylogeny) of a given species. Because they have the same evolutionary history they should show the same phylogenetic relationships and therefore should be combined into one data set to reconstruct a phylogeny and not used separately. To use different types of characters (proteins, DNA, morphology) in exclusion of, or to "prove" the other, is making a false distinction between characters and placing a potentially biased weight on one type of information over another. In addition congruence tests used to produce a phylogenetic tree showing 'congruent' portions of multiple trees may introduce additional error and bias into a phylogenetic study of a group of organisms.

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