Sympatric Speciation / Reproductive Isolation

Sympatric speciation is a mode of speciation in which a new species forms from within a single ancestral species while both the ancestral and the newly forming species continue to occupy the very same geographical region — that is, speciation happens without any physical/geographic separation being involved. It requires that a genetically modified subgroup, favoured by natural selection, becomes reproductively unable to breed successfully with the rest of the parent population even while living alongside it; because there is no physical barrier to prevent occasional contact between the diverging groups, sexual (reproductive) isolation has to be the strongest and most decisive barrier at work here, since it is the only thing actually keeping the gene pools from merging back together. Phenotypic plasticity — the capacity of a single genotype to produce more than one distinct phenotype depending on conditions — has been identified as a potentially important first step that can initiate this kind of …