iological motives include hunger, thirst, the pursuit of pleasure, and the avoidance of pain. An early attempt to specify how these motives affect animal behavior was the ambitious theory of Clark Hull. Hull tried to explain all human and animal motivation using mathematical formulas. Hull borrowed from the concept of homeostasis or biological regulation. His assumption that biological motives followed the pattern of homeostasis is reflected in modern concepts such as the set-point for fat regulation.
Modern theories of hunger and thirst involve multiple factors. For example, obesity is thought to be strongly influenced by genetic factors, but overeating clearly plays buy anabolic steroids online a role in many cases. Some individuals suffer defects in satiety regulation: an extreme example occurs as part of the Prader-Willi syndrome. Thirst also involves multiple factors, such as the volume of water in the stomach, the body as a whole, and in the interior of cells.