Editing Natural selection (section)

===Speciation===
{{Main|Speciation}}
Speciation requires a degree of [[reproductive isolation]]—that is, a reduction in gene flow. However, it is intrinsic to the concept of a [[species]] that [[hybrid (biology)|hybrids]] are selected against, opposing the evolution of reproductive isolation, a problem that was recognised by Darwin. The problem does not occur in [[allopatric]] speciation with geographically separated populations, which can diverge with different sets of mutations. [[E. B. Poulton]] realized in 1903 that reproductive isolation could evolve through divergence, if each lineage acquired a different, incompatible allele of the same gene. Selection against the heterozygote would then directly create reproductive isolation, leading to the [[Bateson–Dobzhansky–Muller model]], further elaborated by [[H. Allen Orr]]<ref>{{cite journal | last1=Orr | first1=H.A. |author-link=H. Allen Orr| title=Dobzhansky, Bateson, and the Genetics of Speciation | journal=Genetics | volume=144 | issue=4 | pages=1331–1335 | year=1996 | doi=10.1093/genetics/144.4.1331 | pmc=1207686 | pmid=8978022 }}</ref> and [[Sergey Gavrilets]].<ref>{{citation |last=Gavrilets |first=S. |title=Fitness Landscapes and the Origin of Species |year=2004 |publisher=Princeton University Press |isbn=978-0-691-11983-0}}</ref> With [[Reinforcement (speciation)|reinforcement]], however, natural selection can favour an increase in pre-zygotic isolation, influencing the process of speciation directly.<ref name="Modes and Mechanisms of Speciation">{{cite journal |title=Modes and Mechanisms of Speciation |author1=Schuler, Hannes |author2=Hood, Glen R. |author3=Egan, Scott P. |author4=Feder, Jeffrey L. | journal=Reviews in Cell Biology and Molecular Medicine | year=2016 | volume=2 | issue=3 | pages=60–93 }}</ref>