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Opium poppy
Brains and the chemicals they run on come from molecules that have been part of the evolutionary marketplace for a very long time. So the "code" that our brains use to operate (and to have fun) is easily found in nature. When we find plant compounds that contain the desired code and consume them -- we hack our own nervous systems. We use "unapproved" means to make changes in how the brain functions. We may even alter its software permanently. (This idea was introduced in a comment to my other blog -- on my home website.)
Indeed, our major neurotransmitters and neuropeptides, including dopamine, serotonin, and opioids, have been around for hundreds of millions of years. I read somewhere that male lobsters stand up and rear their claws when they get a spurt of the peptide vasopressin...which comes from their own brainstems. Vasopressin is an important neurochemical for inter-male aggression in humans! A humbling thought, but not entirely surprising. So not only do we share neurochemicals with extremely ancient ancestors and extremely distant cousins, we even share their functions.
Hominids have been around for a couple of million years, and they've engaged in agriculture for about 5-10,000 years. That's plenty of time to experiment with the profusion of plants that make feel-good chemicals. The odds of hitting the jackpot are greatly enhanced by the simple fact that neurochemicals are cobbled together from existing molecules. Those same molecules got used to make parts of plant bodies based on whatever was lying around in nature. All we had to do was find plants containing molecular compounds similar to our favourite brain chemicals, refine them, and eat them (or smoke them or snort them or shoot them). Coca bushes and opium poppies are prime examples, but even LSD can be synthesized from a common fungus, and alcohol is made when plant sugars rot in the sun.
We are indeed a species who hacks our own brains with the stuff we find in nature. And since we are prone to search for the stuff that makes us feel good, it's almost inevitable that humans would eventually become druggies and alcoholics. I don't think we need to put a moral spin on this. We use the properties of glass to help us to see better when our eyes get weak, we use pieces of wood to help us walk when our legs get weak, and we use chemicals from plants to cure our physical ills and to enhance our mental activities. No, it's not immoral, but it is a bit insidious: neurotransmitters carry the code of our most basic mental functions. When we find substances that mimic that code or extend it to new uses, we are playing around with something fundamental.
These and related ideas are explored in depth in my new book, Memoirs of an Addicted Brain, soon to be released in the US.
