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| Speciation | An evolutionary process in which one species splits into two or more species |
| Microevolution | Evolution change below the species level; change in the allele frequencies in a population over generation |
| Macroevolution | Evolutionary change above the species level. Examples of macroevolutionary change include the origin of a new group of organisms through a series of speciation events and the impact of mass extinction on the diversity of life and its subsequent recovery |
| Biological Species Concept | Definition of a species as a group of population whose members have the potential to interbreed in nature and produce viable, fertile offspring, but do not produce viable, fertile offspring with members of the other such groups |
| Reproductive Isolation | The existence of biological factors the impede members of two species from producing viable, fertile offspring |
| Hybrid | Offspring that results from the mating of individuals from two different species or from two true breeding varieties of the same species |
| Prezygotic barrier | A reproductive barrier that impedes mating between species or hinder fertilization if interspecific mating is attempted |
| Postzygotic | A reproductive barrier that prevents hybrid zygotes produced by two different species from developing i to viable, fertile adults |
| Morphological Species Concept | A definition of species in terms of measurable anatomical criteria |
| Ecological Species Concept | A definition of species in terms of ecological niche, the sum of how members of the species interact with the nonliving and living of their environment |
| Allopatric Speciation | The formation of new species in populations that are geographically isolated from one another. |
| Sympatric Speciation | The formation of new species in populations that live in the same geographic area. |
| Polyploidy | A chromosomal alteration in which the organism possesses more than two complete chromosome sets. It is the result of an accident of cell division. |
| Autopolyploid | An individual that has more than two chromosome sets that are derived from a single species. |
| Allopolyploid | A fertile individual that has more than two chromosome sets as a result of two different species interbreeding and combining their chromosome. |
| Hybrid Zone | A geographic region in which members in which members of different species meet and mate, producing at least some offspring of mixed ancestry. |
| Reinforcement | In evolutionary biology, a process in which a process in which natural selection strengthens prezygotic barriers to reproduction, thus reducing the chances of hybrid formation. Such a process is likely to occur only if hybrid offspring are less fit than members of the parent species. |
| Punctuated equilibria | In the fossil record, long periods of apparent stasis, in which a species undergoes little or no morphological change, interrupted by relatively brief periods of sudden change. |
