Editing Natural selection (section)

===By resource being competed for===

[[File:Pavo cristatus in Barbados Wildlife Reserve 12.jpg|thumb|upright=1.2|right|The [[Peafowl|peacock]]'s elaborate plumage is mentioned by Darwin as an example of [[sexual selection]],<ref name=DarwinSexualSelection>Darwin, Charles (1859). On the Origin of Species (1st edition). Chapter 4, page 88. "And this leads me to say a few words on what I call Sexual Selection. This depends ..." http://darwin-online.org.uk/content/frameset?viewtype=side&itemID=F373&pageseq=12</ref> and is a classic example of [[Fisherian runaway]],<ref name=Greenfield/> driven to its conspicuous size and [[animal coloration|coloration]] through [[mate choice]] by females over many generations.]]
{{Further|Sexual selection}}

Finally, selection can be classified according to the [[Resource (biology)|resource]] being competed for. Sexual selection results from competition for mates. Sexual selection typically proceeds via fecundity selection, sometimes at the expense of viability. [[Ecological selection]] is natural selection via any means other than sexual selection, such as kin selection, competition, and [[Infanticide (zoology)|infanticide]]. Following Darwin, natural selection is sometimes defined as ecological selection, in which case sexual selection is considered a separate mechanism.<ref>{{harvnb|Mayr|2006}}</ref>

Sexual selection as first articulated by Darwin (using the example of the [[Peafowl|peacock]]'s tail)<ref name=DarwinSexualSelection/> refers specifically to competition for mates,<ref>{{harvnb|Andersson|1994}}</ref> which can be ''intrasexual'', between individuals of the same sex, that is male–male competition, or ''intersexual'', where one gender [[mate choice|chooses mates]], most often with males displaying and females choosing.<ref name="Hosken2011">{{cite journal |last1=Hosken |first1=David J. |last2=House |first2=Clarissa M. |title=Sexual Selection |journal=Current Biology |date=January 2011 |doi=10.1016/j.cub.2010.11.053 |pmid=21256434 |volume=21 |issue=2 |pages=R62–R65|s2cid=18470445 |doi-access=free |bibcode=2011CBio...21..R62H }}</ref> However, in some species, mate choice is primarily by males, as in some fishes of the family [[Syngnathidae]].<ref name="Eens">{{cite journal |last1=Eens |first1=Marcel |last2=Pinxten |first2=Rianne |date=5 October 2000 |title=Sex-role reversal in vertebrates: behavioural and endocrinological accounts |journal=Behavioural Processes |volume=51 |issue=1–3 |pages=135–147 |doi=10.1016/S0376-6357(00)00124-8 |pmid=11074317|s2cid=20732874 }}</ref><ref name="Barlow">{{cite journal |last=Barlow |first=George W. |date=March 2005 |title=How Do We Decide that a Species is Sex-Role Reversed? |journal=[[The Quarterly Review of Biology]] |volume=80 |issue=1 |pages=28–35 |doi=10.1086/431022 |pmid=15884733|s2cid=44774132 }}</ref>

<!--[[File:Alligator Pipefish 2.jpg|upright=1.2|thumb|[[Alligator pipefish]] males select females.]]-->
Phenotypic traits can be [[signalling theory|displayed]] in one sex and desired in the other sex, causing a [[positive feedback]] loop called a [[Fisherian runaway]], for example, the extravagant plumage of some male birds such as the peacock.<ref name=Greenfield>{{cite journal |author1=Greenfield, M.D. |author2=Alem, S. |author3=Limousin, D. |author4=Bailey, N.W. |title=The dilemma of Fisherian sexual selection: Mate choice for indirect benefits despite rarity and overall weakness of trait-preference genetic correlation |journal=Evolution |date=2014 |volume=68 |issue=12 |pages=3524–3536 |doi=10.1111/evo.12542 |pmid=25308282 |s2cid=2619084 |doi-access=free }}</ref> An alternate theory proposed by the same [[Ronald Fisher]] in 1930 is the [[sexy son hypothesis]], that mothers want promiscuous sons to give them large numbers of grandchildren and so choose promiscuous fathers for their children. Aggression between members of the same sex is sometimes associated with very distinctive features, such as the antlers of [[Deer|stags]], which are used in combat with other stags. More generally, intrasexual selection is often associated with [[sexual dimorphism]], including differences in body size between males and females of a species.<ref name="Hosken2011"/>