I can't really pick between the evolution one and the nihilist one. I believe it developed as instinctual behaviors necessary for social animals that was just enhanced by our sentience. I don't think that there are any universal moral laws that transcend intelligence or humanity. For instance a planet of aliens that originated completely differently and interact in a very different way would have different morals than us.
I don't think that defining it as an evolutionary process really illuminates anything about morality, because everything is an evolutionary process. Morality is one's conception of how things ought to be, particularly about human behavior. It can be based purely on instinct or it can be the product of a long, reasoned thinking process.
Morality is a limitation that does not always produce the desired result in the situation . Morality is largly a trait associated with kahnism ( ethics ). I prefer applying the result I would like to the situation and act on that .