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analogous structure

structures that do not have a common evolutionary origin but are similar in function

artificial selection

process of breeding organisms with specific traits in order to produce offspring with identical traits


structural adaptation that enables species to blend with their surroundings; allows a species to avoid detection by predators


earliest stage of growth and development of both plants and animal

homologous structure

structures with common evolutionary origins


structural adaptation that enables one species to resemble another species; may provide protection from predators or other advantages

natural selection

process by which individuals that are better suited to their environment survive and reproduce most successfully, also called survival of the fittest

vestigial structure

structure in a present-day organism that no longer serves its natural purpose, but was probably useful to an ancestor

adaptive radiation

divergent evolution in which ancestral species evolve into an array of species to fit a number of diverse habitats

allelic frequency

percentage of any specific allele in a population's gene pool

convergent evolution

evolution in which distantly related organisms evolve similar traits

directional selection

natural selection that favors one of the extreme variations of a trait

disruptive selection

natural selection that favors individuals with either extreme of a trait

divergent evolution

evolution in which species that once were similar to an ancestral species diverge

gene pool

all of the alleles in a population's genes

genetic drift

alteration of allelic frequencies in a population by chance events

genetic equilibrium

condition in which the frequency of alleles in a population remains the same over generations

geographic isolation

occurs whenever a physical barrier divides a population, which results in individuals no longer being able to mate; can lead to the formation of a new species


idea that species originate through a gradual change of adaptations


any species with multiple sets of the normal set of chromosomes; results from errors during mitosis or meiosis

punctuated equilibrium

idea that periods of speciation occur relatively quickly with long periods of genetic equilibrium in between

reproductive isolation

occurs when formerly interbreeding organisms can no longer mate and produce fertile offspring


process of evolution of new species that occurs when members of similar populations no longer interbreed to produce fertile offspring within their natural environment

stabilizing selection

natural selection that favors average individuals in a population

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