A recent study found genetic evidence of multiple instances and species combinations where genetic material has passed the species boundary in bears (a process called introgression by geneticists). Specifically, species with evidence of past intermingling were (1) brown bear and American black bear, (2) brown bear and polar bear, (3) American black bear and Asian black bear, (4) bears currently distributed in Asia (sloth bear, Malayan sun bear and Asian black bear). Overall, this study shows that evolution in the bear family ("Ursidae") has not been strictly , but instead showed complex evolutionary relationships.