A collective group of people will be more successful than an individual alone, in terms of survival of the fittest. In order to be a productive, successful, efficient, and advanced society, we must cooperate efficiently; it is essential to the survival of the society. You could say that the individual's greatest interest is his own achievement due to our inherent goal of being the dominant man, but in order to succeed to one's fullest potential, the individual must be a part of the society. Everyone in society would face conflict if they did not take into consideration the fact that everyone's main goal is their own success. Therefore, "morality" arises; morality being a set of social rules to abide by in order to maximize the success of the society, which ultimately maximizes the success of the individual. And being social animals, we have empathy, which allows us to naturally understand this phenomenon and act accordingly. Because we have this sense of empathy, and because the need for society to abide by these rules in order to be successful, morality is subconsciously placed on such high regard. If everyone were to commit immoral acts, the society would collapse. Therefore, even though it may not be apparent on the small-scale, immoral acts are detrimental to the society, and ultimately to the individual. Perhaps organized religion developed as a tool to reinforce the necessity of morality; because the individual's afterlife is at risk of eternal punishment, the individual will make damn sure that they abide by the rules. But because the individual's greatest interest is their own success, the authority figures of religion (or any form of authority) could use this to their advantage to satisfy their desire for power and control of the masses.