Some fictional cavemen knuckle-walk or drag the knuckles of their long arms on the ground, but scientists do not agree on whether human beings evolved from ancestors who really knuckle-walked on the ground the way gorillas do. One team of scientists said humans evolved from a tree-living ancestor, like chimpanzees did, because of the way our wrist bones are. Another team of scientists wrote that "Australopithecus anamensis" and "Australopithecus afarensis", extinct relatives of humans, probably knuckle-walked.