| Term | Definition |
|---|
| Adaptive radiation | The emergence of numerous species from a common ancestor introduced into an environment that presents a diversity of new opportunities and problems. |
| Allometric growth | The variation in the relative rates of growth of various parts of the body, which helps shape the organism. |
| Allopatric speciation | A mode of speciation induced when an ancestral population becomes segregated by a geographic barrier or is itself divided into two geographically isolated subpopulations. |
| Allopolyploid | A common type of polyploid species resulting from two different species interbreeding and combining their chromosomes. |
| Autopolyploid | An individual that has more than two chromosome sets, all derived from a single species. |
| Biological species concept | Definition of a species as a group of populations whose members can produce fertile offspring. |
| Ecological species concept | Defining species in terms of ecological roles (niches). |
| Heterochrony | Evolutionary change in the timing or rate of an organism's development. |
| Homeotic gene | Any of the genes that control the overall body plan of animals and plants by controlling the developmental fate of groups of cells. |
| Macroevolution | Evolutionary change above the species level. |
| Microevolution | Evolutionary change below the species level. |
| Morphological species concept | Defining species by measurable anatomical criteria. |
| Paedomorphosis | The retention in an adult organism of the juvenile features of its evolutionary ancestors. |
| Paleontological species concept | Definition of species based on morphological differences known only from the fossil record. |
| Phylogenetic species concept | Definition of a species as a set of organisms with a unique genetic history- that is, as one branch on the tree of life. |
| Polyploidy | A chromosomal alteration in which the organism possess more than two complete chromosome sets. |
| Postzygotic barrier | Any of several species-isolating mechanisms that prevent hybrids produced by two different species from developing into fertile adults. |
| Prezygotic barrier | A reproductive barrier that impedes mating between species or hinders fertilization of ova if interspecific mating is attempted. |
| Reproductive isolation | The existence of biological factors (barriers) that impede members of two species from producing fertile hybrids. |
| Speciation | The origin of new species in evolution |
| Species | A group whose members possess similar anatomical characteristics and have the ability to interbreed. |
| Species selection | A theory maintaining that species living the longest and generating the greatest number of species determine the direction of major evolutionary trends. |
| Sympatric speciation | A mode of speciation occurring as a result of radical change in the genome of a subpopulation, reproductively isolating the subpopulation from the parent population. |
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