Evolution of psychoactive substances

[Aquila]

I have been thinking about psychoactive plant substances like marijuana (from the cannabis plant), opium and its derivatives morphine, heroine and codeine (from the opium poppy).

We know what these substances do to the human system, but how did they evolve? What advantage, if any, do these chemicals have to the plants from which they are obtained? For example, do these chemicals ward off predators?

Similar thoughts about analgesics like aspirin, derived from salicylic acid from willow bark. What evolutionary advantage, if any, does this substance give to the willow?

 

[Professor Yaffle]

I haven't read the whole paper, but this paragraph suggests it might address this issue to some extent:

Evolutionary biologists studying plant–herbivore interactions have convincingly argued that many plant secondary metabolites, including alkaloids such as nicotine, morphine and cocaine, are potent neurotoxins that evolved to deter consumption by herbivores (Karban & Baldwin 1997; Roberts & Wink 1998).1 On the other hand, neurobiology's reward model sees interactions between drugs and the nervous system as rewarding and reinforcing. Hence, in their current forms, neurobiology's reward model and evolutionary biology's punishment model appear to be incompatible.

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2367444

 

[Zeuzzz]

Well catnip certainly doesn't gain any advantage from being psychoactive to cats. My cats slowly got through an entire plant over the course of a month, and all seemed very depressed when it was finished.

It probably didn't help that they starting injecting it by the end of the month.

 

[Aquila]

It probably didn't help that they starting injecting it by the end of the month.

And thanks for the article, Professor Yaffle.