Why do humans follow the same morals as each other?

The same reason wolves and dolphins (and all pack animals) have the same basic rules (morals) no matter which pack or group. We are pack animals and we evolved our morals because they are what's in our best interest to survive. Natural selection picks what works, not what is bad for a species. What group is more likely to survive, one that cares about the rest of the pack and works as a team, or one that only looks out for number 1?