Recombinational Speciation: hybridization between 2 species gives rise to a new lineage that is both fertile and true breeding, but is reproductively isolated from both parental species.
Forms novel genotype that is homozygous for several chromosome arrangements that differentiate the parental species
Certain rare hybrid genotypes can be fitter than parentals, though most hybrids are less fit / at some kind of disadvantage.
Can be produced in lab with many generations of artificial selection.
It is also possible in nature. The well-documented cases are flowers, but it also seems possible in animals. More study is needed to confirm the animal cases, however. Amazon mollies are hybrids, aren’t they?
Hybrids between parentals are almost* completely sterile, but surviving F2 and later generations gradually increase in fertility. The hybrid species can actually be stabilized in a few generations. The new species are usually ecologically isolated from the parentals.
*If all hybrids between the species were completely sterile, then recombinational speciation would not be possible.
