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| evolution | a heritable change in the characteristics within a population from one generation to the next; the development of new types of organisms from preexisting organisms over time |
| natural selection | the process by which individuals that are better adapted to their environment survive and reproduce more successfully than less well adapted individuals do ; a theory to explain the mechanism for evolution |
| fitness | in evolutionary theory, a measure of an individual's hereditary contribution tot he next generation |
| vestigial structures | a structure in an organism that is reduced in size and function and that may have been complete and functional in the organism's ancestors |
| fossil | the trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock |
| homologous structures | a physical characteristic in different organisms that is similar because it was inherited from a common ancestor |
| analogous structures | a physical structure, present in multiple species, that is similar in function but different in form and inheritance |
| microevolution | a change int he allele frequencies of a population of organisms from generation to generation |
| gene pool | all of the genes of the reproductively active members of a population |
| allele frequency | the proportion of gene copies in a population of a given allele, expressed as a percentage |
| phenotype frequency | the ration of individuals with a particular phenotype to the total number of individuals in a population |
| Hardy-Weinberg genetic equilibrium | the principle that states that the frequency of allels in a population does not change over generations unless outside forces act on the population |
| Immigration | the movement of an individual or group into a population |
| Emigration | the movement of an individual or group out of a population |
| Gene flow | the movement of genes into our out of a population due to inbreeding |
| Genetic drift | the random change in allele frequency in a population |
| Founder effect | a decrease in genetic variation caused by the formation of a new population by a small number of individuals from a larger population |
| sexual selection | an evolutionary mechanism by which traits that increase the ability of individuals to attract or acquire mates appear with increasing frequency in a population; selection in which a mate is chosen on the basis of a particular trait or traits |
| speciation | the formation of a new species as a result of evolution |
| morphology | the study of the structure and form of an organism |
| biological species concept | the concept that a species is a population of organisms that can interbreed but cannot breed with other populations |
| geographic isolation | the physical separation of populations due to geographic barriers that prevent interbreeding |
| reproductive isolation | the inability of members of a population to successfully interbreed with members of another population of the same or a related species |
| gradualism | a model of evolution in which gradual change over a long period of time leads to biological diversity |
| punctuated equilibrium | a model of evolution in which short periods of drastic change in species, including mass extinctions and rapid speciation, are separated by long periods of little or no change |
