Narcotic plants such as betel nut, coca and tobacco may have been used throughout the ages to ward off hunger and fatigue, such that drug cravings are now part of our genetic makeup.

“Psychotropic compounds may have helped our ancestors survive by providing neurotransmitters - brain food - in harsh environments when resources were very scarce,” says Edward Hagen, Ph.D., of the Institute for Theoretical Biology at Humboldt-Universität zu Berlin in Germany.

Cannabis (marijuana) was historically used throughout West Africa and Asia and appears in written records from 2000 B.C. as a medicine in China. The cola nut, one of the original ingredients in Coca Cola, is a popular stimulant in East Africa today and has been since the Europeans first made contact. Betel nut was chewed at least 13,000 years ago in Timor; tobacco and coca were used in the Americas in antiquity and the Australian shrub pituri was long used as a narcotic by aborigines.

These substances are portable and don’t decay, like many foods. “They represent an ideal instant energy source for people living in situations where food supply is uncertain, or during travel, when supplies might not last,” says Roger Sullivan, Ph.D., of the University of Auckland in Australia.

Sullivan’s theory, published in the journal Addiction, challenges evolutionary views of substance abuse, which he believes fail to adequately explain prehistoric drug use. Sullivan and co-author Hagen are the first to postulate that the use of psychotropic substances under harsh conditions could possibly be an attempt to replenish neurotransmitters, specifically.