Humans ate Neanderthals.

From LiveScience:

Nobody's sure why [Neanderthals] disappeared... Some say climate change did them in. Other scientists figure competition with humans was the issue.

But Fernando Rozzi, of Paris's Centre National de la Recherche Scientifique, say our ancestors ate them. The evidence: a Neanderthal jawbone with marks similar to those left on bones of deer and other animals that Stone Age humans butchered, according to the Daily Mail.

"Neanderthals met a violent end at our hands and in some cases we ate them," Rozzi says.

Not everyone is ready to buy the theory yet.

And lest you pity the Neanderthals, know that they are thought to have resorted to cannibalism in tough times, too. "There is strong evidence suggesting that these Neanderthals were eaten" by their own kind, said Antonio Rosas of the Museo Nacional de Ciencias Naturales in Madrid back in 2006 (regarding his completely separate study). "That is, long bones and the skull were broken for extraction of the marrow, [which] is very nutritious." Mmm.