Evolution: Difference between revisions

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{{evolution3}}

In [[biology|Biologicallybiology]], '''evolution''' is change in the [[heritability|inherited]] [[trait (biology)|traits]] of a [[population]] of organisms from one generation to the next. These changes are caused by a combination of three main processes: variation, reproduction, and [[natural selection]]. [[Gene]]s that are passed on to an organism's offspring [[gene expression|produce]] the inherited traits that are the basis of evolution. These traits vary within populations, with organisms showing [[genetic variation|heritable differences]] in their traits. When organisms reproduce, their offspring may have new or altered traits. These new traits arise in two main ways: either from [[mutation]]s in genes, or from the transfer of genes between populations and between species. In species that [[sexual reproduction|reproduce sexually]], new combinations of genes are also produced by [[genetic recombination]], which can increase variation between organisms. Evolution occurs when these heritable differences become more common or rare in a population.

Two major mechanisms drive evolution. The first is [[natural selection]], a process causing heritable traits that are helpful for survival and reproduction to become more common in a population, and harmful traits to become more rare. This occurs because individuals with advantageous traits are more likely to reproduce, so that more individuals in the next generation inherit these traits.<ref name=Futuyma/><ref name=Lande>{{cite journal |author=Lande R, Arnold SJ |year=1983 |title=The measurement of selection on correlated characters |journal=Evolution |volume=37 |pages=1210&ndash;26} |doi=10.2307/2408842}}</ref> Over many generations, [[adaptation]]s occur through a combination of successive, small, random changes in traits, and natural selection of those variants best-suited for their environment.<ref name="Ayala">{{cite journal |author=Ayala FJ |title=Darwin's greatest discovery: design without designer |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=104 Suppl 1 |issue= |pages=8567–73 |year=2007 |pmid=17494753 |url=http://www.pnas.org/content/104/suppl.1/8567.full |doi=10.1073/pnas.0701072104}}</ref>