"All your life you live so close to the truth, it becomes a permanent blur in the corner of your eye, and when something nudges it into outline it is like being ambushed by a grotesque" wrote Tom Stoppard in Rosencrantz and Guildenstern are Dead. Something I believe is true even though I cannot prove it, is that both cannibalism and slavery were prevalent in human prehistory. Neither belief commands specialist academic consensus and each phenomenon remains highly controversial, their empirical "signatures" in the archaeological record being ambiguous and fugitive.
Truth and belief are uncomfortable words in scholarship. It is possible to define as true only those things that can be proved by certain agreed criteria. In general, science does not believe in truth or, more precisely, science does not believe in belief. Understanding is understood as the best fit to the data under the current limits (both instrumental and philosophical) of observation. If science fetishized truth, it would be religion, which it is not. However, it is clear that under the conditions that Thomas Kuhn designated as " normal science" (as opposed to the intellectual ferment of paradigm shifts) most scholars are involved in supporting what is, in effect, a religion. Their best guesses become fossilized as a status quo, and the status quo becomes an item of faith. So when a scientist tells you that "the truth is . . .", it is time to walk away. Better to find a priest.
Until recently, most archaeologists would be inclined to say that the truths about cannibalism and about slavery are that each has been sharply historically limited and that each is a more or less aberrant cultural phenomenon. The reason for such a belief is that it is only in a small number of cases that either thing be proved beyond reasonable doubt. But I see the problem in the starting point.
If we shift our background expectations and say that coercing a living person to do one's bidding is perhaps the very first form of property ownership ("the slavery latent in the family" to use Marx and Engels' telling phrase), and that eating the dead (as very many wild vertebrates do) makes sense in nutritional and competitive terms, then the archaeologist's duty is to empirically establish those times and places where slavery and cannibalism had ceased to exist. The only reason we have hitherto insisted on proof-positive rather than proof-negative in relation to these phenomena is that both seem grotesque to us now, and we have rather a high opinion of our natural civility. This is the most interesting point, and the focus of my attention is how culturally-elaborated mechanisms of restraint and inter-personal respect emerged and allowed such refined scruples.