That's a really tough one.. as we have no proof either way, it's always going to be debatable.... and a big debate at that!
I think certain things are logic.. in terms or morality.. we do know it varies from culture .. for instance most people believe killing is immoral... but cannibals and head-hunters did it.. However, even they didn't do it or want it done to their family... so there was still some moral sense there?
Animals have varying but still strong codes of behaviour and almost ethics...