Udayana,
I think it's just a case of tools for the job. As society changes different belief/mythology can be found to work better, some things don't work as well or fall out of fashion. Actually I think Harari describes this quite well in his broad brush history - though there is loads of detail to object to.
Yes, but I was pointing out the category difference: "this painting is beautiful" and "there's a dragon in my garage" could each be described as beliefs that work better or not, but one relates to a subjective opinion and the other to an objective fact. When there's no-one to express an opinion on the painting there is no opinion on the painting; when there's no-one to feed the dragon, he's still there (or not) regardless.
That's the issue with morality: it's in the former category, though some really, really want it to be in the latter - generally for very bad reasons, like the
argumentum ad consequentiam, as a proof for "God" etc.
Altruism is certainly a tool developed during evolution but how people behave just depends on how they feel and circumstances at any time. In many ways the most equal societies were those of the hunter gatherers but most of the time they seem to have been engaged in fierce warfare with competitive tribes (reading Jared Diamond rather than Harari).
But I don't think that the exercise of altruism "just depends on how they feel and circumstances at any time" at all. Rather it's instinctive and for the most part automatic, and it's been observed and documented in may species other than out own. It's also been modelled mathematically, and computer simulations show the "quants" programmed to have it to flourish better than those that do not. It takes a supervening factor to override that - dogma being one such, and religious dogma being the example that's most relevant here.