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A form of natural selection that favors both extreme phenotypes over the intermediate phenotype. An example is the finch beak size in environments with two food sources of very different sizes.

A sharp reduction in the size of a population due to environmental events (like earthquakes, floods), which reduces genetic variation. An example is the Cheetah population bottleneck.

A change in the DNA sequence that can lead to genetic diversity. An example is the development of new alleles in a population.

A case of genetic drift that occurs after a small number of individuals colonize a new area, leading to a change in allele frequencies. An example is the relatively high frequency of the Ellis-van Creveld syndrome in the Amish population.

A type of natural selection that favors the average phenotype over the extreme varieties. An example is the birth weight in humans where too low or too high weight has lower survival rates.

A trait that increases an organism's ability to survive and reproduce in its environment. An example is the camouflage in stick insects.

The process by which populations evolve to become distinct species. An example is the emergence of different finch species in the Galapagos Islands.

The process by which genetic diversity is maintained in a population by selection due to heterozygote advantage or frequency-dependent selection. An example is the maintenance of multiple alleles for the beta-globin gene.

A random process that can cause gene frequencies to change over time, especially in small populations, leading to a loss of genetic variation. An example is the founder effect in island populations.

A process where organisms better adapted to their environment tend to survive and produce more offspring. An example is the development of antibiotic resistance in bacteria.

A mode of natural selection in which some individuals out-reproduce others because they are better at securing mates. An example is the bright plumage of male peacocks.

A principle stating that the genetic variation in a population will remain constant from one generation to another in the absence of disturbing factors. The equation is

A process in which an extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype. An example is the increase in body size in certain fish populations.

The transfer of genetic variation from one population to another. An example is the movement of pollen between plant populations by the wind.