Terence McKenna — the Witoto tribe — by Fabrizio Cassetta

"But the thing about tryptamines is they cannot be taken orally because they're denatured by an enzyme found naturally in the human gut called monoamine oxidase. They can only be taken orally if taken in conjunction with some other chemical that denatures the MAO. 

The fascinating things are that the beta-carbolines found within that liana are MAO inhibitors of the precise sort necessary to potentiate the tryptamine. 

So you ask yourself a question:

How, in a flora of 80,000 species of vascular plants, do these people find these two morphologically unrelated plants that when combined in this way, create a kind of biochemical version of the whole being greater than the sum of the parts?

Well, we use that great euphemism, "trial and error," which is exposed to be meaningless. But you ask the Indians, and they say "The plants talk to us."

Well, what does that mean? This tribe, the Cofan, has 17 varieties of ayahuasca, all of which they distinguish a great distance in the forest, all of which are referable to our eye as one species. 

And then you ask them how they establish their taxonomy and they say, "I thought you knew something about plants. I mean, don't you know anything?" And I said, "No." 

Well, it turns out you take each of the 17 varieties on the night of a full moon, and it sings to you in a different key. Now, that's not going to get you a PhD at Harvard, but it is much more interesting than counting stamens."

— Wade Davis