Department of Anthropology

Tobacco is the number one risk factor for disease burden in developed countries, and of all substance use categories carries the highest mortality risk, accounting for an estimated 12% of global morality. Worryingly, its use is rapidly increasing in the developing world. Current neurobiological theory of drug use is based on the observation that all addictive drugs induce changes in activity of dopaminergic circuitry, interfering with reward processing, and thus enhancing drug seeking and consumption behaviors. Current theory of drug origins, in contrast, views almost all major drugs of abuse, including nicotine, cocaine and opiates, as potent plant neurotoxins that evolved to punish and deter herbivores. According to this latter view, plants should not have evolved compounds that reward or reinforce plant consumption. Mammals, in turn, should not have evolved reinforcement mechanisms easily triggered by toxic substances. Situated in an ecological context, therefore, drug reward is a paradox. We are investigating several potential resolutions of this paradox. For example, humans, like other animals, might have evolved to co-opt plant neurotoxins. Specifically, a propensity to seek out and consume toxic plants might have evolved as a means to fight pathogens.