Table 1.

Hypothetical evolutionary stages with empirical examples along the ‘extended speciation continuum', with effects under secondary contact and hybridization, with special attention on undifferentiated and differentiated sex chromosomes. This table is supposed to show evolutionary tendencies as described in the text. Note that stages along the ‘extended speciation continuum' do not necessarily correspond to absolute divergence times as in some species, speciation proceeds more rapidly than in others, i.e. stages should be preferentially compared within a certain radiation of organisms. Evidence for Aspidoscelis lizards is equivocal since sex chromosomes are only known in very few species.