According to a study published in the latest issue of Current Anthropology
Homo antecessor who lived in Europe a million years ago ate members of competing clans just as another item on the menu. Remains found in a cave near Burgos, Spain reportedly showed that the processing of cannibalistic meals was no different than any other (i.e., not ritual oriented) and that lesser animal forms were available for food (i.e., cannibalism not from starvation). Homo antecessor was the last common ancestor of the lineage to Neanderthal and the African lineage that gave rise to modern man.
The humans-as-food determination negates other possibilities, such as cannibalism for ritual's sake, or cannibalism due to starvation. In this oldest known case of humans eating humans, other food was available to the diners, but human flesh was just part of their meat mix.
Homo antecessor facts:
Homo antecessor picture: