Morality is a system of values placed upon certain actions and opinions. An example would be that some people think that the marriage of a man to another man is moralbased on the principles of utilitarianism. However, others think that such a thing is immoral. Some people believe that marriage of any sort is amoral(without morality). Therefore, these people would have differing moral codes.
Some biologists argue that morality grew out of behavioral rules shaped by evolution. They see social behaviors displayed by some primates as the precursors of human morality. They cite examples such as rhesus monkeys which, when given a chance to get food by pulling a chain that delivers a shock to another monkey, have been known to starve themselves for a considerable time.<ref> "Primates and Philosophers" by Frans de Waal</ref>