Why did they evolve the ability to produce a chemical compound so closely related to serotonin, the neurotransmitter, that it can slip across the blood-brain barrier and temporarily take charge of the mammalian brain? Was it a defense chemical, intended to poison mushroom eaters? That would seem to be the most straightforward explanation, yet it is undermined by the fact the fungus produces the hallucinogen almost exclusively in its “fruiting body”—that part of the organism it is happiest to have eaten. Was there perhaps some benefit to the mushroom in being able to change the minds of the
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