The Evolution of Drugs

Drug cultures are endlessly varied, but drugs in general are more or less ubiquitous among our species. The celebrated list of ‘human universals’ compiled by the anthropologist Donald E. Brown includes ‘mood - oi consciousness-altering techniques and/or substances’ as one of the essential components of human culture, along with music, conflict resolution, language and play. But there is little consensus regarding the origins of this universal impulse, which essential human traits it serves and how far back into our past its roots extend. Some have posited a primordial moment of discovery when proto-humans first encountered plants that expanded their minds to generate new forms of thought and language. Others have argued that such a moment may be encoded in our shared origin myths, perhaps in stories of a fruit that bestowed the knowledge of good and evil. Nevertheless, it seems that the discovery of intoxicants is a drama in which even the remote human past is a very recent episode. The plants that contain these substances evolved alongside our animal antecedents, and many developed such chemicals because of their physiological effects on creatures like ourselves. We were taking drugs long before we were human.

Drugs, and our response to them, are the product of an elaborate evolutionary dance between the plant and animal kingdoms that has been underway for at least 300 million years. Coniferous trees began producing tannins to deter fungal parasites, and bitter saponines to repel woodboring insects. Flowering plants, when they emerged during the Cretaceous period, developed more complex nitrogen-based alkaloids in their fruit and leaves. These compounds, typically bitter to the taste, are toxic to some animals but produce pleasant effects in others. The capsaicin in chilli peppers, for example, is both a deterrent and a stimulant, killing parasites but encouraging the release of endorphins in mammals (while birds, on which the chilli depends for its dispersal, lack the chemical receptor that causes it to function as an irritant). Plant families often generate a spectrum of related alkaloids with both mental and physical effects: the nightshades, for example, manufacture the poisons in raw potatoes, the bug-killing and brain-rewarding nicotine in tobacco, and the hallucinogenic deliriants in daturas and belladonna.