Editing Sympatric speciation (section)

===Current state of the controversy===
Evolutionary theory as well as mathematical models have predicted some plausible mechanisms for the divergence of species without a physical barrier.<ref name="Kondrashov & Kondrashov 1999"/> In addition there have now been several studies that have identified speciation that has occurred, or is occurring with gene flow (see section above: evidence). Molecular studies have been able to show that, in some cases where there is no chance for allopatry, species continue to diverge. One such example is a pair of species of isolated desert palms. Two distinct, but closely related species exist on the same island, but they occupy two distinct soil types found on the island, each with a drastically different pH balance.<ref name="Savolainen et al 2006"/> Because they are palms they send pollen through the air they could freely interbreed, except that speciation has already occurred, so that they do not produce viable hybrids. This is hard evidence for the fact that, in at least some cases, fully sympatric species really do experience diverging selection due to competition, in this case for a spot in the soil.

This, and the other few concrete examples that have been found, are just that; they're few, so they tell us little about how often sympatry actually results in speciation in a more typical context. The burden now lies on providing evidence for sympatric divergence occurring in non-isolated habitats. It is not known how much of the earth's diversity it could be responsible for. Some still say that panmixia should slow divergence, and thus sympatric speciation should be possible but rare (1). Meanwhile, others claim that much of the earth's diversity could be due to speciation without geographic isolation.<ref name="Nosil 2008">{{cite journal |doi=10.1111/j.1365-294X.2008.03715.x |title=Speciation with gene flow could be common |year=2008 |last1=Nosil |first1=Patrik |journal=Molecular Ecology |volume=17 |issue=9 |pages=2103–6 |pmid=18410295|s2cid=164288751 |doi-access=free |bibcode=2008MolEc..17.2103N }}</ref> The difficulty in supporting a sympatric speciation hypothesis has always been that an allopatric scenario could always be invented, and those can be hard to rule out – but with modern molecular genetic techniques can be used to support the theory.<ref name="Nosil 2008"/>

In 2015 [[Cichlid]] fish from a tiny volcanic crater lake in Africa were observed in the act of sympatric speciation using DNA sequencing methods. A study found a complex combination of ecological separation and [[mate choice]] preference had allowed two [[Ecomorphology|ecomorphs]] to genetically separate even in the presence of some genetic exchange.<ref>{{cite news |url=http://phys.org/news/2015-12-darwin-puddle-species-emerge-geographic.html |title='Darwin's puddle' shows how new species can emerge without geographic separation |date=18 December 2015 |work=Phyorg.com }}</ref><ref>{{cite journal |title=Genomic islands of speciation separate cichlid ecomorphs in an East African crater lake |last1=Malinsky |first1=M. |display-authors=etal |date=2015 |journal=Science |doi=10.1126/science.aac9927 |pmid= 26680190|volume=350 |issue=6267 |pages=1493–1498 |pmc=4700518|bibcode=2015Sci...350.1493M }}</ref>