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[[Image:Darwin_tree_4.jpg|left|thumb|"Darwin's Tree of Life: the first-known sketch by Charles Darwin of an evolutionary tree describing the relationships among groups of organisms."]

[[Image:Darwin_tree_4.jpg|left|"Darwin's Tree of Life: the first-known sketch by Charles Darwin of an evolutionary tree describing the relationships among groups of organisms."]

In [[biology]], '''evolution''' is the change in the [[heritability|inherited]] [[trait (biology)|traits]] of a [[population]] from generation to generation. These traits are the [[gene expression|expression]] of [[gene]]s that are copied and passed on to offspring during [[biological reproduction|reproduction]]. [[Mutation]]s in these genes can produce new or altered traits, resulting in heritable differences ([[genetic variation]]) between organisms. New traits can also come from transfer of genes between populations, as in [[migration]], or between species, in [[horizontal gene transfer]]. Evolution occurs when these heritable differences become more common or rare in a population, either non-randomly through [[natural selection]] or randomly through [[genetic drift]].

In [[biology]], '''evolution''' is the change in the [[heritability|inherited]] [[trait (biology)|traits]] of a [[population]] from generation to generation. These traits are the [[gene expression|expression]] of [[gene]]s that are copied and passed on to offspring during [[biological reproduction|reproduction]]. [[Mutation]]s in these genes can produce new or altered traits, resulting in heritable differences ([[genetic variation]]) between organisms. New traits can also come from transfer of genes between populations, as in [[migration]], or between species, in [[horizontal gene transfer]]. Evolution occurs when these heritable differences become more common or rare in a population, either non-randomly through [[natural selection]] or randomly through [[genetic drift]].