Is there an innate moral sense? The fashion has been to side with Nietzsche and say that there isn't, because the values of different cultures vary so widely. But, are these values really differing expressions of the same, underlying sense? In contrast, almost all human beings, who are not psychologically damaged, have a sex drive. But, there are, as we know, wildly different expressions of that sex drive. And those expressions also differ throughout cultures. Underlying them though is the same drive to rut.
So, what about empathy? The example that used to come up in philosophy was: "I can't imagine a culture in which it would be morally acceptable to throw a child into a burning building. Nor have I ever heard of one. Couldn't this just be a universal human belief?"
Psychology is taking up the question as well. Maybe certain emotional responses are wired into us. Maybe we are, after all, generally empathetic. It's certainly a good argument against belief systems.