Editing Selfish genetic element (section)

=== Species extinction ===
Perhaps one of the clearest ways to see that the process of natural selection does not always have organismal fitness as the sole driver is when selfish genetic elements have their way without restriction. In such cases, selfish elements can, in principle, result in species extinction. This possibility was pointed out already in 1928 by Sergey Gershenson<ref name=":5" /> and then in 1967, [[W. D. Hamilton|Bill Hamilton]]<ref>{{cite journal | vauthors = Hamilton WD | title = Extraordinary sex ratios. A sex-ratio theory for sex linkage and inbreeding has new implications in cytogenetics and entomology | journal = Science | volume = 156 | issue = 3774 | pages = 477–88 | date = April 1967 | pmid = 6021675 | doi = 10.1126/science.156.3774.477}}</ref> developed a formal population genetic model for a case of segregation distortion of sex chromosomes driving a population to extinction. In particular, if a selfish element should be able to direct the production of sperm, such that males bearing the element on the Y chromosome would produce an excess of Y-bearing sperm, then in the absence of any countervailing force, this would ultimately result in the Y chromosome going to fixation in the population, producing an extremely male-biased sex ratio. In ecologically challenged species, such biased sex ratios imply that the conversion of resources to offspring becomes very inefficient, to the point of risking extinction.<ref>{{Cite book|title=Allee effects in ecology and conservation|last=Franck.|first=Courchamp|date=2009|publisher=Oxford University Press|isbn=978-0199567553|oclc=929797557}}</ref>