Editing Speciation (section)

=== Allopatric ===
{{Main|Allopatric speciation}}

During allopatric (from the ancient Greek ''allos'', "other" + ''patrā'', "fatherland") speciation, a population splits into two geographically isolated populations (for example, by [[habitat fragmentation]] due to geographical change such as [[mountain formation]]). The isolated populations then undergo genotypic or [[Phenotype|phenotypic]] divergence as: (a) they become subjected to dissimilar [[Selection (biology)|selective]] pressures; (b) different [[mutation]]s arise in the two populations. When the populations come back into contact, they have evolved such that they are reproductively isolated and are no longer capable of exchanging [[gene]]s. [[Small population size#Genetic consequences|Island genetics]] is the term associated with the tendency of small, isolated genetic pools to produce unusual traits. Examples include [[insular dwarfism]] and the radical changes among certain famous island chains, for example on [[Komodo (island)|Komodo]]. The [[Galápagos Islands]] are particularly famous for their influence on Charles Darwin. During his five weeks there he heard that [[Galápagos tortoise]]s could be identified by island, and noticed that [[finch]]es differed from one island to another, but it was only nine months later that he speculated that such facts could show that species were changeable. When he returned to [[England]], his speculation on evolution deepened after experts informed him that these were separate species, not just varieties, and famously that other differing Galápagos birds were all species of finches. Though the finches were less important for Darwin, more recent research has shown the birds now known as [[Darwin's finches]] to be a classic case of adaptive [[evolutionary radiation]].<ref>{{cite journal |last=Sulloway |first=Frank J. |author-link=Frank Sulloway |date=September 30, 1982 |title=The ''Beagle'' collections of Darwin's finches (Geospizinae) |url=http://darwin-online.org.uk/content/frameset?viewtype=text&itemID=A86&pageseq=1 |journal=Bulletin of the British Museum (Natural History), Zoology |volume=43 |issue=2 |pages=49–58}}</ref>