Few doubt that human feeding behavior is part of larger biology regulatory system of energy stores, but the extent to which eating behavior is controlled by these biology systems and how much is due to responses to environmental stimuli is presently under debate. The results of a series of studies are presented which have attempted to determine the responsiveness of human feeding behavior to some of the “classic” biological variables that have conventionally been used to argue the biological basis of eating behavior. When humans are challenged with either overfeeding, underfeeding, or alterations of the caloric density of the diet, they fail to demonstrate precise caloric compensation. When challenged with changes in environmental stimuli, on the other hand, humans appear to be very sensitive to changes in portion size, the number of people with whom they eat, the amount that others eat and the variety of foods available. Other more chronic influences demonstrate that body weight appears to change when people move from one area of the world to another, when they enter the college environment, or when they either marry or break up. It is argued that because humans appear to be more responsive to the external environment than internal biological cues, it should be possible to curb or even reverse the epidemic of obesity by changing aspects of the external environment or human interactions with environmental variables rather than changing their internal environment through pharmacology.