ALDH1B1 is present in mammals but missing from birds and fish. The high degree of AA sequence conservation between ALDH2 and ALDH1B1 suggests that the latter may be the product of a gene duplication event that occurred some time after the avian-land animal split around 310 MYA. Future analyses should consider other species, including amphibians and reptiles, in order to verify and more accurately pinpoint this evolutionary event.
