Whether or not this is true, it doesn't affect the ontological status of "ought": the qualia of ought, like other qualia, are physically implemented, and not rationally derived. You can have all the intermediaries you want (I posited generalization, pattern-matching, and other rational analysis as intermediaries rather than "culture", because this is how we get good results out of our other intrinsic capabilities and instincts), but at the end what makes it an ought is the physical instantiation of a module that converts states of affairs into goal-directed action.

Any cognition that fails to be able to engage this mechanism tends to lose its status as an "ought". For instance, we tend not to be able to condone the agonizing torture of a modest number of our own children in order to considerably improve the well-being of billions of people. "This isn't how things actually work, so don't worry about it" is not a satisfactory way to assuage our revulsion. Instead, we stammer that while it is, by premise, an efficient way to accomplish a stated goal that seems suspiciously like a lot of goals that we endorse, we very much ought not condemn our own children to agonizing torture. ("Our own" is necessary because we can demonize "them" and then commit ghastly atrocities against "them".)

And then we turn around and think that we ought to punish transgressors in non-iterated prisoner's dilemma games (if we're allowed to punish, even at cost to ourselves, even if we can't ever interact with them again).

I don't think we've left these roots behind nearly as far as you say, and regardless, I don't think we have any choice but to be stuck being as naturally implemented as we actually are. We have a lot of latitude, it turns out, to regulate our idea of what is right and wrong, but we're ultimately constrained by the actual implementation of our sense of ought, even if we can use culture and whatnot to engage in understanding and regulation of that sense; and we are doomed to ultimately refer to the physical instantiation of ought to ground any reasoning about what we should or should not do, because there simply isn't anything else around.

(Also, I think the evolution of culture and behavioral modernity is not really traceable to the upper paleolithic to any great extent. Chimps and dolphins and crows, among others, have culture; and modernity is a sprawling mess of behaviors many of which have probably had various different degrees of selection far back into our evolutionary history. But that's another topic.)