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adaptive radiation

process by which a single species or small group of species evolves into several different forms that live in different ways; rapid growth in the diversity of a group of organisms

allopatric speciation

the formation of a new species as a result of an ancestral population's becoming isolated by a geographic barrier.

directional selection

occurs when natural selection favors one of the extreme variations of a trait

disruptive selection

natural selection that favors individuals with either extreme of a trait; tends to eliminate intermediate phenotypes

founder effect

when a few individuals become isolated from a larger population, this smaller group may establish a new population whose gene pool isn't reflective of the source population

genetic drift

The gradual changes in gene frequencies in a population due to random events


a model of evolution in which gradual change over a long period of time leads to biological diversity

hardy weinberg principle

principle that allele frequencies in a population will remain constant unless one or more factors cause the frequencies to change.

punctuated equilibrium

evolutionary model suggesting species often diverge in spurts of relatively rapid change, followed by long periods of little change

sexual selection

A form of selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates (example: bigger antlers on a deer make that deer more likely to attract a mate)

spontaneous generation

hypothesis (disproven) stating that life could arise from nonliving matter

stabilizing selection

natural selection that favors intermediate variants by acting against extreme phenotypes

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