The genetic model of speciation requires physical (geographical) isolation of populations as a sine qua non for the formation of new species. Only under geographical isolation spontaneous changes in DNA (genes, regulatory sequences, etc) can accumulate and finally lead to the reproductive (postzygotic) isolation of the populations when they come in contact again. The genetic model implies that speciation, formation of new species, can occur only in allopatry, i.e. when species-to-be populations are physically isolated so that they form and maintain diverging gene pools until the accumulated genetic changes make impossible reproduction of hybrids between two populations.
This theoretical assumption is rejected by facts in nature: vast empirical evidence unambiguously show that sympatric speciation occurs, new species are formed from populations living in the same range, i.e. populations that are not physically prevented from interbreeding. Empirical evidence for sympatric speciation is more solid than for allopatric speciation. Further, this evidence proves that no accumulation of gene changes occur or is necessary for formation of new species. That changes in genes are not involved in formation of sympatric species is also proven by the fact that under favorable conditions these species produce reproductively viable offspring.
How does the speciation occur if no changes in genes are involved in the process?
Examination of verified cases of sympatric speciation shows that the isolation of popula tions in sympatry is related to changes in mate preferences for certain characters (or changes in host preferences as it occurred in formation of new insect species) in a group of individuals within the original population. Both changes in mate preferences and host preferences are determined by epigenetic changes (don’t forget that no changes in genes are involved in these cases of speciation) in neural circuits responsible for both changes in mate preferences and changes in host preferences. Since mechanisms of speciation in cases of sympatric speciation are neural mechanisms, we call this form of speciation sensorydriven- or neuro-cognitive sympatric speciation.