The moral principles of which you are talking about are simply a social convention. You could argue that this social convention is based on psychological traits that derive from our evolutionary history. However, both conventions and traits deriving from evolution are either "right" or "wrong" only when there is an external source of morality upon which they can be judged. Conventions and evolutionary traits are not sources of morality in themselves. For example, evolution has programmed my brain in such a way that I feel that eating fat is desirable. This is so because our ancestors struggled against starvation for most of their evolutionary history. However, since I am a rational being, I can get to the conclusion that this psychological trait is harmful given my present environment. Hence, I resist that which has been imposed on me by evolution. Likewise, I may resist my urges to be compassionate, if I realize that compassion is harmful to me or to my group. We must conclude therefore that psychological traits derived from evolution are not right or wrong in themselves. Also, slavery was an acceptable social convention in most of the world during most of the history of mankind. If social conventions were always right, and if the majority were always right when it comes to morality, we would be forced to conclude that all abolitionist movements were immoral throughout most of the history of mankind. That means that social conventions are neither wrong nor right in themselves.