Revealing the paradox of drug reward in human evolution

Neurobiological models of drug abuse propose that drug use is initiated and maintained by rewarding feedback mechanisms. However, the most commonly used drugs are plant neurotoxins that evolved to punish, not reward, consumption by animal herbivores. Reward models therefore implicitly assume an evolutionary mismatch between recent drug-profligate environments and a relatively drug-free past in which a reward centre, incidentally vulnerable to neurotoxins, could evolve... We sketch some potential resolutions of the paradox, including the possibility that humans may have evolved to counter-exploit plant neurotoxins.

This is an interesting paper, although I suspect that most readers will find its addiction-pathology paradigm a little grating. Starting from the premise that human neurophysiology evolved in a drug-free Eden (irony entirely intentional), the researchers run into the inevitable roadblocks that this view presents: humans clearly did not evolve in a psychoactive-free environment, and are remarkably well adapted to metabolizing these 'toxins.'

The paradigm of drugs mimicking true [evolutionary] fitness rewards by hijacking the brain's reward centre deserves to be more thoroughly dismissed than it is here; I wonder if the researchers are aware of the visual acuity benefits of psilocybin, for instance? All in all, a shame that the writers did not have the courage to admit that the only way to resolve their 'paradox' is to conclude that humans have continued to incorporate psychoactive plants in their diet precisely because they confer genuine fitness.