Another interesting way to word a question-separating morals from ethics and asking how moral/ethical decisions are made. To make sure I understood the question I felt compelled to find the definition of both morals and ethics. According to the American Heritage Dictionary (2nd College Edition) (this is the reference material used for all definitions henceforth), "morals" is defined as "...rules of conduct with reference to standards of right and wrong." Ethics, on the other hand, is defined as "... a system of moral principles and values." Now, perhaps I'm being simple-minded, but it seems as though the two are more alike than different. Strangely, I've heard people try to distinguish them (at least one of whom had a PhD), so I must be wrong. At any rate, I'm going to combine the two and answer the question thusly: Are decisions of right and wrong based more on character or on social behavior?
I think the answer to this question is actually very fluid. It changes over time just as we, as people, change. I believe that when we're very young and still very "Id-oriented" (to take a phrase from Freud), few, if any, decisions are based on morality. In fact, it's amoral decisions witnessed by our parents (and from now on, when I use this term I'll mean or our first moral guides, whoever they may be) that begin to shape our internal moral/ethical barometer. As we get a little older, we start to realize that the universe doesn't begin and end with us. As this sinks in, we begin to make decisions based, not only on our needs, but on environmental/societal needs as well. As we reach adulthood, we tend to have a fairly stable view of right and wrong and our ethical decision making is fairly well ingrained. Obviously, people mature at different rates and exact ages are impossible to discern, but that's a general account of our moral/ethical growth.
Some people never grow or fully develop a moral center. Reasons for this are many: a lack of parental (or any leader) guidance; environmental cues sending ethically mixed messages; extreme circumstances (such as poverty) which skew ethical views, etc. All-in-all, though, assuming a person has a relatively stable set of moral/ethical standards, where does it come from? Without sounding too wishy-washy, I think it comes from a combination of factors, though I would lean more heavily on one than the other to answer the question.
When we are still very young, our parents give us guidance as to what is right and wrong. If they instill strong moral values with strict definitions of right and wrong, we will have a moral center as we enter adulthood. This isn't to say that social cues and behavior can't reshape our sense of right and wrong-of course they can. But, without a sound moral base, which we would all call character, the lessons learned later in life, won't necessarily have as much meaning.
Morals and ethics: decisions of character or social behavior? If we want to distinguish morals from ethics we could do so as follows: ethics are based on morals, therefore, without morals we have no ethics. I only bring up this point to illustrate the following. Yes, social behavior influences our moral decision making. But, without a strong character base, social influences would mean nothing. Therefore, ultimately, our decisions of right versus wrong are based on character.