Sympatric speciation in the genomic era

Sympatric speciation has been of key interest to biologists investigating how natural and sexual selection drive speciation without the confounding variable of geographic isolation. The advent of the genomic era has provided a more nuanced and quantitative understanding of the different and often complex modes of speciation by which sympatric sister taxa arose, and a reassessment of some of the most compelling empirical case studies of sympatric speciation. However, I argue that genomic studies based on contemporary populations may never be able to provide unequivocal evidence of true primary sympatric speciation, and there is a need to incorporate palaeogenomic studies into this field. This inability to robustly distinguish cases of primary and secondary ‘divergence with gene flow’ may be inconsequential, as both are useful for understanding the role of large effect barrier loci in the progression from localised genic isolation to genome-wide reproductive isolation. I argue that they can be of equivalent interest due to shared underlying mechanisms driving divergence and potentially leaving similar patterns of coalescence.