| A | B |
|---|
| Gene flow | The process of genes moving from one population to another. |
| Genetic drift | The phenomenon by which allele frequencies in a population change as a result of random events. |
| Assortative mating | The selection of a mate based on similarity of characteristics. |
| Stabilizing selection | Individuals with an average form of a trait have the highest fitness. |
| Directional selection | Individuals that display a more extreme form of a trait have greater fitness than those with the average form of the trait. |
| Disruptive selection | Individuals with either extreme variation of a trait have greater fitness than individuals with the average form of the trait. |
| Sexual selection | When females tend to choose males they mate with based on certain traits. |
| Speciation | The process of species formation. |
| Morphology | Internal and external structure and appearance of an organism. |
| Biological species concept | A species is a population of organisms that can successfully interbreed but cannot breed with other groups. |
| Geographic isolation | The physical separation of members of a population. |
| Reproductive isolation | Barriers to successful breeding between population groups in the same area. |
| Prezygotic isolation | Isolation that occurs before fertilization. |
| Postzygotic isolation | Isolation that occurs after fertilization. |
| Gradualism | The theory that evolution occurs at a slow, gradual rate. |
| Punctuated equillibrium | The theory that evolution occurs rapidly followed by long periods of inactivity. |
