Sympatric Speciation

Sympatric speciation is the process by which new species evolve from a single ancestral species while inhabiting the same geographic region. Unlike allopatric speciation, which requires geographic isolation, sympatric speciation depends on disruptive selection or other mechanisms that create reproductive barriers without spatial separation. The concept is central to debates about the speed and predictability of evolutionary diversification, with some biologists arguing that sympatric speciation is rare and others contending it is underestimated because it produces cryptic species that are difficult to detect. The theoretical connection to adaptive dynamics is that branching points under disruptive selection provide the phenotypic divergence necessary for sympatric speciation to proceed. Whether this divergence reliably leads to complete reproductive isolation remains one of the open questions in evolutionary theory. Additional mechanisms such as assortative mating and habitat choice may interact with disruptive selection to complete the speciation process.