Cannibalism, for instance. There are Neanderthal bones which do seem to have been stripped of their flesh as if for...well, dinner.
I could have had my Neanderthals constantly at war, but that would have muddied the other strands of the story. I needed a reason why my Neanderthals could be cannibals without being savages.
ThenI remembered the marvellous books by Sir Arthur Grimble about the Gilbert and Ellice Islands, and his account of ancestor worship there. Might not cannibalism be a form of respect shown to an ancestor?
It’s certainly be a form of practical recycling, if nothing else.
I also remembered Douglas Adams’ cow in The Restaurant at the End of the Universe.
And between my memories of the books of these two brilliant writers, the cannibalism of my Neanderthals began to make absolutely perfect sense.