Unit 3: This unit addresses an important issue in understanding human behavior -- the basic sources of that behavior. At different times in human history our behavior has been attributed to biological qualities, to such thing as instincts. As we have come to understand ourselves we also have changed the view as to the basis of behavior. Today we see our behavior to be based increasingly in the social system of which we are a part. This unit explores these questions and concludes with a discussion of language in humans and in animals.