JewishAtheist wrote a question asking about whether morality is just an excuse for the selfishness in people, here. I have basically expressed all my views on morality scattered all over this blog so some of this will be repetative.
The first point, and perhaps the most important point, with regard to morality is the confusion of morality with empathy. This is a scientific error of thinking. The purely scientific way to discuss questions of morality is to ask how did they evolve? And when one asks such questions one is stuck discussing questions of empathy, altruism, compassion, and kindness. This is not equivalent to morality. There have been a myriad of civilizations with their own moral codes. Many of these moral codes did not corellate with these feel-good feelings. There were civilizations that were against helping the weak as they believed the weak are weak as punishment from their past lives so helping them is evil. This kind of moral code went entirely against any evolved sense of empathy. Most of the morals that people have believed in have extremely little to do with any evolved feeling within people. Indeed, most morals are against human natures, and as such if morality was evolved then it would not contradict people's natures. Therefore, the question of morality cannot be studied scientifically. At least not with natural selection.
I myself separate feelings of altruism and compassion from morality. So that I can tell people, "I have no morals". If they were to ask me why I would help another, I will simply say that I do not consider the desire to help others as a "moral". Morals have always meant something more than just empathy. And since I do not hold any higher interpretation of morals I reject all of morality and live without morals. I would encourage all people to take the same approach. Rejecting morals is in a way rejecting God. When one rejects God one loses his belief that reaffirms his life, so one needs to learn to live himself without being able to reaffirm himself. I view morals in a same way. When one rejects morals one has the challenge of not having any reaffirmation of ones actions, so the challenge is to be strong enough to be able to live without needing to reaffirm your actions.
Besides what kind of moral code is, "be nice to those people who deserve it" (which is essentially all I do, it is nice to be nice, and that is it, I need no greater reason than that)? Moral codes are very complex. They involve honor, sanctity, discipline, loyality, holiness, pureness, so on and so forth. The desire to just act nice is not something which I even consider to be a moral.
Then JewishAtheist talks about morality as being used for our selfishness. The truth is that morality, for its history, has always meant the complete opposite. Wanting to do something to yourself, such as pleasuring yourself, is wicked and people must move away from that. Morality has been a rebellion to people's natures. I strongly disagree with that. People acting in their self-interests is a very recent concept. One of the influences Adam Smith brought to the world was the idea that there is nothing wrong about wanting to act for your self-interest - his book Theory of Moral Sentiments was in a way a prelude to his economic theory as a moral defense.
The selfish aspect to morality is extremely recent and through out past history it has meant something entirely different.
So if morality cannot be explained through natural selection, and if morality is a rejection to people's own desires then from whence did it originate from? I have had my own idea to where morality came from. I believe that the function of morality was used as a tool to control the masses. Indeed, morality is authoratarian, it commands people to act in a particular manner. Its original goal was to control masses of people. Today the morals that are present are really mostly remants of dead moral systems that are not used anymore for domination, but that was their original function. If you are interested to the history behind how morals first developed you can read this - which is entirely my own guess, but it does sound reasonable.