Were Psychoactive Plants Designed for a Purpose or Just random evolution at work?

The plant secondary defense compounds that humans have labeled “psychoactive” were not “designed for human use”, or even primate use, for that matter. The very tiny number of these chemical compounds that humans find “useful” or “pleasurable”, represents an insignificant fraction of the vast array of chemical compounds plants use in their unremitting evolutionary arms race with those organisms which prey upon them. Most of these compounds not only are not “pleasurable”, but are anywhere from mild to deadly toxins for humans. An entire course in evolutionary ecology would be required to discuss the selection pressures that led plants to develop these compounds, so suffice that the few we like (whether legal like caffeine and nicotine, or illegal like cannabis) are more of a fluke of chemistry rather than design. They evolved for - and are extremely useful for - entirely different “purposes”.If you’d like to get into specifics, let me know.

Excellent response, NJ. The only part of your post with which I would disagree ("Overall I see so many lucky rolls so as to rule out the total possibility of random chance X natural selection."), would likely be too far off topic to address in this thread. Which is the exact position of any scientist worthy of the name when the evidence available for any hypothesis is lacking, ambiguous, or equivocal. Well said.Something you pointed out in your response which is quite apropos was: I think yours is an especially apt question when we're talking about chemical and physical defenses plants evolved in the New World tropics, where humans are relative newcomers to the scene. A mere 13,000 years (well, even if we postulate the 25,000 years some authors argue) simply isn't enough time for human-derived selection pressures to have caused this kind of adaptation - especially at the extraordinarily low level of "exploitation for psychotropic effects" and limited numbers of species humans find useful in that context compared with the vast numbers that have similar adaptations. If, as the OP suggests, these few organisms really WERE designed for human use, what is the explanation for all the OTHER defenses plants have developed? Isn't more logical, as you state, that the few species humans find useful were merely serendipitous?

I was unclear, evidently. I meant that, at the level of selection an ad hoc, occasional use of a particular psychoactive species (not an intensively cultivated plant or animal - or one under constant deliberate selection like your Heikea japonica example) would generate, there would be insufficient time for and likely insufficient pressure for, complex chemical compounds to have developed as an adapation to that pressure.Oh, and the heike/samurai story may in fact be an urban legend. There are a number of other crab species whose shells also resemble a human face, for instance Paradorippe granulata, Corystes cassivelaunus, and other "faced" or "marked" crabs. Something to do with the physical constraints of the shell during development.

Heh. Actually, the urban legend part was about the fishermen actually throwing them back. Apparently that isn't the general case.Anyway, off topic for this thread. Was I able to clarify my point concerning the limited selection pressures on psychoactive plants? When humans have put specific plants under selection pressure (through cultivation, for instance), a lot of times it's specifically to reduce the toxins. One example is potatoes (the ones sold in the US f'rinstance contain <20% of the glycoalkaloids in the "wild" type found in the Andes). Tomatoes, broccoli, apples (seeds), etc, all have been bred to reduce toxicity. Think about that next time you're in a health-food store and see bins of raw cashews for sale - you're gonna destroy your liver eating them unless they are from the one or two varietals that have had the toxins bred down.