A different spin on things:

Taking narcotics may be part of our evolutionary inheritance

IF DRUGS are so bad for us, why do so many people use them? Because they helped our ancestors survive, argue two anthropologists.

Our predilection for psychotropic substances is usually seen as a biological accident. The conventional view is that drugs fool the brain into thinking it is getting a reward when in fact it isn’t.

But anthropologists Roger Sullivan of the University of Auckland and Edward Hagen of the University of California at Santa Barbara point out that our ancestors were exposed to plants containing narcotic substances for millions of years. In the April issue of Addiction, they argue that we are predisposed to drug-taking because we evolved to seek out plants rich in alkaloids.

Link.