Cline (biology)
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In biology, a cline is a measurable gradient in a single characteristic of a species across its geographical range. Clines usually have a genetic, or phenotypic character. They can show either smooth,
Bergmann's Rule demonstrated showing the difference in size between a larger northern fox, whose range spans colder regions, and a smaller desert fox, whose range is primarily in hot regions
Reinforcement (speciation)
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Reinforcement is a process of speciation where natural selection increases the reproductive isolation between two populations of species. This occurs as a result of selection acting against the produc
Alfred Russel Wallace proposed in 1889 that isolation could be strengthened by a form of selection.
Darwin's finches by Gould