A sense of morality can be explained by natural selection as I posted in your previous thread. Simply put: species that killed each other died off, leaving only those that don't kill each other.
I don't know about the former part of this statement, but stem cells come from more than aborted babies
But who decides how the proper way is to behave? People all have different ideas of what's in the best interest of species survival though. For example you could say that killing elderly or disabled people is morally acceptable because they hold back the rest of society by draining the species' resources and contributing nothing (this matter was also the subject
of a well-written Star Trek episode). Many things that people would consider to be a moral-based matter have nothing to do with species survival, such as whether it's morally wrong to torture animals, eat human flesh, wear no clothes in public, physically punish your children, or be involved in petty theft.
I simply don't think Natural Selection is sufficient to explain morality as we know it in the real world. It's not even consistent when it comes to the subject of murder, because everywhere you go, the definition of murder can also be different. In the US i'd be fairly certain virtually everyone (as well as the written laws) would agree that being killed for peacefully protesting - with no malicious behavior - is an act of murder, while in North Korea or Iran it would be just considered a justified death because you went against the State, as the State would be considered the means of ethnic or social survival (so going against it could be interpreted by them as going against the survival of your people).
Meanwhile religions such as Christianity and Islam are eager to specifically define what they do and don't consider murder, and careful study of their texts can give you a fairly specific picture of what is and isn't okay to do under the rules of those religions.
