Is behavior determined by fate or can we shape our future?

Do sociology and other social sciences such as anthropology, psychology, assume that our behavior is determined by events over which we have no control--or can they allow that there is a free will in each person, which is unpredictable?
For the most part the social sciences assume that people operate with a free will and will act in unpredictable ways. Having said that there are certain tendencies of humans that are verifiable and provide clues about past human behavior and serve as a way to hypothesize what future human behavior will be. For example people tend to live in communities. More advanced societies tend toward specialization of labor. People tend to work together to overcome nature. People tend to congregate in homogenous groups and shun those they view as "outsiders".

However, in spite of these tendencies that seem to be true of most people groups throughout history, there is always the tendency of any individual within a group to exercise his free will and rebel against established conventions. Christians who insisted on believing in the bodily resurrection of Jesus to the point that they were willing to be crucified or fed to lions rather than recant their faith is an example. Buddhist monks who have chosen to set themselves on fire is another. Recently there have been accounts of individuals walking into a school or business and shooting other individuals they don't know for no apparent reason or personal gain. In situations like these, professionals are left wondering why a person did that or what triggered their emotions in such a way?