Editing Sexual selection (section)

=== Toolkit of natural selection ===

[[File:Protarchaeopteryx 4713.JPG|thumb|''[[Protarchaeopteryx]]'' was flightless, but had feathers, perhaps used in courtship, that [[Exaptation|pre-adapted]] it for flight.|alt=Artist's reconstruction of a proto-bird fossil as if it used its small wings in courtship display]]

Sexual selection may explain how characteristics such as feathers had survival value at an early stage in their evolution. The earliest proto-birds such as ''[[Protarchaeopteryx]]'' had well-developed feathers but could not fly. The feathers may have served as insulation, helping females incubate their eggs, but if proto-bird courtship combined displays of forelimb feathers with energetic jumps, then the [[Origin of avian flight|transition to flight]] could have been relatively smooth.<ref name="Clarke 2013">{{cite journal |last=Clarke |first=J. |title=Feathers Before Flight |journal=Science| volume=340 | issue=6133 |date=9 May 2013 |doi=10.1126/science.1235463 |pages=690–692 |pmid=23661746 |bibcode=2013Sci...340..690C |s2cid=31802107 }}</ref>

Sexual selection may sometimes generate features that help cause a species' extinction, as has historically been suggested for the giant antlers of the [[Irish elk]] (''Megaloceros giganteus'') that became extinct in [[Holocene]]<ref>{{Cite journal |last1=van der Plicht |first1=J. |last2=Molodin |first2=V. I. |last3=Kuzmin |first3=Y. V. |last4=Vasiliev |first4=S. K. |last5=Postnov |first5=A. V. |last6=Slavinsky |first6=V. S. |date=15 April 2015 |title=New Holocene refugia of giant deer (Megaloceros giganteus Blum.) in Siberia: updated extinction patterns |url=https://www.sciencedirect.com/science/article/pii/S027737911500075X |journal=Quaternary Science Reviews |volume=114 |pages=182–188 |doi=10.1016/j.quascirev.2015.02.013 |bibcode=2015QSRv..114..182V |issn=0277-3791}}</ref> Eurasia<ref name="Gould 1974">{{cite journal |last=Gould |first=Stephen Jay |author-link=Stephen Jay Gould |year=1974 |title=Origin and Function of 'Bizarre' Structures – Antler Size and Skull Size in 'Irish Elk', Megaloceros giganteus |journal=Evolution |volume=28 |issue=2 |pages=191–220 |doi=10.2307/2407322 |pmid=28563271 |jstor=2407322 }}</ref> (although climate-induced habitat deterioration and anthropogenic pressure are now considered more likely causes).<ref>{{Cite journal |last1=Lister |first1=Adrian M. |last2=Stuart |first2=Anthony J. |date=2019-01-01 |title=The extinction of the giant deer Megaloceros giganteus (Blumenbach): New radiocarbon evidence |url=https://www.sciencedirect.com/science/article/pii/S1040618219300333 |journal=Quaternary International |series=SI: Quaternary International 500 |volume=500 |pages=185–203 |doi=10.1016/j.quaint.2019.03.025 |bibcode=2019QuInt.500..185L |issn=1040-6182}}</ref> It may, however, also do the opposite, driving species divergence—sometimes through elaborate changes in [[sex organs|genitalia]]<ref>{{Cite journal |last=Eberhard |first=William G. |date=24 March 2009 |title=Evolution of genitalia: theories, evidence, and new directions |url=https://repository.si.edu/bitstream/handle/10088/9845/stri_Eberhard_2010.pdf |journal=Genetica |volume=138 |issue=1 |pages=5–18 |doi=10.1007/s10709-009-9358-y |pmid=19308664 |s2cid=1409845 }}</ref>—such that new species emerge.<ref>Hosken, David J.; Stockley, Paula. "[http://www.sexologia.ulusofona.pt/biblio/Indice_files/Sexual%20selection%20and%20genital%20evolution.pdf Sexual selection and genital evolution] {{webarchive |url=https://web.archive.org/web/20171012045147/http://www.sexologia.ulusofona.pt/biblio/Indice_files/Sexual%20selection%20and%20genital%20evolution.pdf |date=12 October 2017}}." ''Trends in Ecology & Evolution'' 19.2 (2004): 87–93.</ref><ref>Arnqvist, Göran. "[http://heart.sdsu.edu/~website/biology_307/pdfs/genitalia.pdf Comparative evidence for the evolution of genitalia by sexual selection] {{webarchive |url=https://web.archive.org/web/20120127135826/http://heart.sdsu.edu/~website/Biology_307/pdfs/genitalia.pdf |date=27 January 2012}}." Nature 393.6687 (1998): 784.</ref>   Sexual selection often interacts with natural selection to drive [[speciation]].<ref>Maan, M.E.; Seehausen, O. "Ecology, sexual selection and speciation". ''Ecology Letters'', 2011 Jun; 14(6). pp. 591-602. doi: 10.1111/j.1461-0248.2011.01606.x. PMID 21375683.</ref>