There are many myths about humans eating human flesh. While some historians believe that cannibalism was an accepted practice in some tribal societies, this view has been disputed by William Arens, an anthropologist at the State University of New York at Stony Brook.
In his 1980 book The Man-Eating Myth (Oxford University Press 1980), Arens challenges the claim that that cannibalism was ever a socially approved custom anywhere in the world. Arens doesn't deny that cannibalism has been practiced, but questions the assumption that it was ever routine, ritualized, or acceptable. Instead, incidents of cannibalism were driven by famine, mental illness, or aberrant belief in mysticism or religion.
As it turns out, one of the most famous cases of American cannibalism may not be true. In 2006, archaeologists who researched Alder Creek, Nevada - the site where the ill-fated Donner pioneer party became trapped during the winter of 1846 and allegedly resorted to cannibalism - announced that "there's no physical evidence that the family who gave the Donner Party its name had anything to do with cannibalism." The findings did not disprove the sensational stories that emerged after the survivors were rescued, but found no physical evidence to support the claims.