Evolutionary Psychology or Evolutionary Psychological Reasoning of Morality?

Many evolutionary psychologists are explaining the origins of morality and revealing things about what probably happened in the plister scene. This is quite unnerving in some ways atd perhaps it shows that our moral beliefs are just really the sorts of things which small groups of early hominids evolved to believe there's no objective morality. But i don't think all such arguments simply commit the genetic fallacy. To say that is too quick. And yet, on the other hand, it is very difficult to explain just why evolutionary psychology should, in fact, undermine our moral convictions ar our moral beliefs.