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group of organisms so similar to one another that they can breed and produce fertile offspring


trace of an organism from the past


theory that states that natural disasters such as floods and volcanic eruptions shaped Earth's landforms and caused the extinction of some species (Cuvier)


principle that states that the changes in landforms result from slow changes over a long period of time (Hutton)


theory that states that the geologic processes that shape Earth are uniform through time (Lyell)


differences in physical traits of an individual from the group to which it belongs


inherited trait that is selected over time because it allows organisms to better survive in their environment

artificial selection

process by which humans modify a species by breeding it for certain traits


all of the individuals of a species that live in the same area


measure of an organism's ability to survice and produce offspring relative to other members of a population


the study of the distribution of organisms around the world

homologous structure

body part that is similar in structure on different organisms, but performs different functions (ex. limbs of humans and bat wings)

analogous structure

body part that is similar in function as a body part of another organism, but is structurally different (ex. moth wings and bird wings)

vestigial structure

remnants of an organ or structure that functioned in an earlier ancestor (ex. wisdom teeth or tail bones)


study of fossils or extinct organisms

gene pool

collection of alleles found in all of the individuals of a population

allele frequency

proportion of one allele, compared with all the alleles for that trait, in the gene pool


observable change in the allele frequency of a population over a few generations

directional selection

pathway of natural selection in which one uncommon phenotype is selected over a more common phenotype

stabilizing selection

pathway of natural selection in which intermediate phenotypes are selected over phenotypes at both extremes

disruptive selection

pathway of natural selection in which two opposite, but equally uncommon, phenotypes are selected over the most common phenotype

gene flow

physical movement of alleles from one population to another

genetic drift

change in allele frequencies due to chance alone, occurring most commonly in small populations

bottleneck effect

genetic drift from an event that drastically reduces the size of a population

founder effect

genetic drift that occurs after a small number of individuals colonize a new area

sexual selection

selection in which certain traits enhance mating success, traits are, therefore, passed on to offspring

reproductive isolation

finals stage in speciation, in which members of isolated populations are either no longer able to mate or mo longer able to produce viable offspring

behavioral isolation

isolation between populations due to differences in courtship or mating behavior

geographic isolation

isolation between populations due to physical barriers

temporal isolation

isolation between populations due to barriers related to time, such as differences in mating periods or differences in the time of day that individuals are most active

convergent evolution

evolution toward similar characteristics in unrelated species, resulting from adaptations to similar environmental conditions

divergent evolution

evolution of one or more closely related species into different species; resulting from adaptations to different environmental conditions


process in which two or more species evolve in response to changes in each other

punctuated equilibrium

theory that states that speciation occurs suddenly and rapidly followed by long periods of little evolutionary change


evolution of two or more species from ome ancestral species

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