Do you ever eat when you're not hungry? Would you rather eat your least favorite meal with a favorite person than eat your favorite meal alone? Does the environment in which you eat affect how much you eat? If you answer any of these affirmatively, then your biological drives are being modified by other needs.
The body should regulate its own weight, yet many people eat when they are not hungry. To begin with, many people respond to external cues--the attractive restaurant, good company. They are responding to eating as a social event. Perhaps they are being driven by their need for social companionship.
What motivates people to eat too much or to snack monotonously between meals when they are alone? We cannot be so sure, But some believe that these people overeat because food is a substitute for what they lack emotionally. a response to emotional deprivation. In cases like these, emotions may be the motives that actually channel behavior.
Then there are people who clean up their plates whether they are hungry or not. Perhaps these are the people who were told as children, "clean up your plate!" Perhaps a leftover drive to please a parent in response to the need to feel loved and accepted.
All these behavioral patterns represent the way a biological drive is modified by other needs-social and psychological. Drinking and sleeping, the other biological needs, are affected in similar ways.