Bracing against the wind  

Saturday, January 10, 2004

Parasites and Co-evolution of Recreational Drugs

I was listening to NPR some time ago and they had a parasite expert on the air. He was talking about Toxoplasma gondii. Toxoplasma gondii lives in cats, but the way it spreads is via rats. When it infects the rat, the rat becomes less risk averse, it becomes attracted to the smell of cats, and it has a slower reaction time. In humans, the Toxoplasma has a similar effect. In fact, people infected by it are more likely to own cats!

There's one parasite (Euhaplorchis californiensis) that reproduces in birds. This bloodfluke first infects snails that eat the birds' droppings. Them they travel through the water to fish, which they infect by swimming into the gills, finding a blood vessel, and then a nerve, ending up on the surface of the brain. The fish then become more likely to jump out of the water or splash near the surface, which makes them about 30 times more likely to be eaten by birds, thus completing the fluke's life cycle.

Parasites evolved over time to control the minds of their hosts. They get their hosts to engage in behavior that promotes their existence.

This got me thinking about the various recreational drugs that we find in nature. Might it be that these blood-brain barrier crossing drugs similarly evolved to the benefit of their parent species?

Is it possible that the effects of psilocybin on animals actually helps promote the survival of the psilocybin? How about the effects of cannabis or cocaine?

Cows and sheep fall into behavior patterns and rarely migrate outside their territory unless given an environmental nudge. Psychoactive mushrooms grow in cow and sheep feces. They cannot survive without animals. They spread via animal locomotion. An animal can run from a fire. A mushroom can not. Their vested interest, for millions of years, was for animals to not fall into predictable patterns, and to, instead, range far and wide.

Indeed, mushrooms may cause animals to break their established pattern of behavior and go to new fields in order to ensure their own spread and survival, since they have no locomotive ability on their own.

More generally, many plants and mushrooms have hallucinogenic effects on animals. Animal brain receptors and these compounds have certainly co-evolved. Indeed, there's a "cannaboid receptor" in our brain. Perhaps these are intended to produce behaviors that promote the survival of the psychoactive species?

Bob Ross in the Best of the Joy of Painting, was known to say "Think like a tree". Maybe he meant that... literally.

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