The ancestors of the bison, or buffaloes, of Catalina Island off the California coast arrived as movie extras in 1924. Scientists have always thought they were more likely to be pure-bred than many of the other buffalo that roam North America, because they’ve effectively been in isolation. Turns out it ain’t so. Nearly half the animals shipped off the island have maternal cow genes. Scientists believe the cross breeding probably occurred before the buffalo were shipped to Catalina — and nothing since 1924 has selected against it.
P.S. As the commenter to our original piece pointed out, nobody seems to have looked for bison genes in cattle. Why not?