A deep dive into how parasites hijack our behavior and how we evolved to resist them

On Slate Star Codex (previously), Scott Alexander breaks down Invisible Designers: Brain Evolution Through the Lens of Parasite Manipulation, Marco Del Giudice's Quarterly Review of Biology paper that examines the measures that parasites take to influence their hosts' behaviors, and the countermeasures that hosts evolve to combat them.

Diligent readers will know that parasites manage some incredible feats of behavior modification (one of Scott Westerfeld's best novels looks at vampirism as a form of parasitic behavior modification and it's just great).

It's a truism that the predator carves the prey and the prey carve the predator. Del Giudice's investigations into parasite tactics and countermeasures lead him to hypothesize that perhaps human variation is driven by responses to parasites' attempts at behavior modification (for example, humans have a lot of variability in our major histocompatibility complex genes, which mean that our immune systems can readily distinguish between our cells and invasive ones).

It's a super-interesting paper, and Alexander's breakdown is a great path into it.

Sixth, you use antiparasitic drugs as neurotransmitters. This is the kind of murderous-yet-clever solution I expect of evolution, and it does not disappoint. Several neurotransmitters, including neuropeptide Y, neurokinin A, and substance P are pretty good antimicrobials. The assumption has always been that the body kills two birds with one stone, getting its signaling done and also having some antimicrobials around to take out stray bacteria. But Del Giudice proposes that this is to prevent parasites from hijacking the signal; any parasite that tried to produce or secrete an antiparasitic drug would die in the process.