The Good, The Bad, and The Hangry

Hunger seems like a simple phenomenon: the stomach rumbles until it’s fed, then it’s quiet until it rumbles again. Why, then, does it shape so much behavior that, at least on the surface, has so little to do with food? Part of the answer can be gathered from observations of other animals. For some of them, a little starvation seems to confer a survival advantage. In rodents, hunger appears to heighten sensory perception and speed up mental processing. In other animals, hunger leads to riskier but potentially more rewarding behavior. Two years ago, scientists at the Max Planck Institute of Neurobiology, in Germany, showed that hungry fruit flies will tolerate elevated levels of carbon dioxide—which, inhaled at sufficient concentrations, will knock them unconscious—as long as the smell of food is also present. Similarly, in the Pacific Northwest, juvenile walleye pollock were observed to school in looser, less defensive formations when hungry. They huddled together only when their chopped-squid rations became more generous, which made dodging predators seem more important than finding food.
 These side effects of hunger—intensified awareness, greater persistence, bolder risk assessments—also exist in humans.