Geophagia—the practice of eating dirt, especially claylike soils, is something animals and people have been doing for millennia.
The standard reference guide for psychiatrists—the fourth edition of the Diagnostic and Statistical Manual for Mental Disorders (DSM-IV)—classifies geophagia as a subtype of pica, an eating disorder in which people consume things that are not food, such as cigarette ash and paint chips.
Investigators have observed geophagia in more than 200 species of animals, including parrots, deer, elephants, bats, rabbits, baboons, gorillas and chimpanzees. Geophagia is also well documented in humans, with records dating to at least the time of Greek physician Hippocrates (460 B.C.).
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[Excerpted from Scientific American]