Scott Alexander explores a theory suggesting that complex features of human biology evolved as defenses against parasite manipulation, discussing its implications for understanding psychiatric medications and biological complexity. Longer summary

This post discusses a theory proposed by Marco del Giudice in his paper 'Brain Evolution Through The Lens Of Parasite Manipulation'. The theory suggests that many complex features of human biology, particularly in neurotransmitter systems, evolved as defenses against parasite manipulation of host behavior. The post outlines various strategies that organisms might use to defend against such manipulation, including complicated signaling cascades, feedback loops, pulse-based communication, individual variability, and the use of antimicrobial substances as neurotransmitters. Scott Alexander explores the implications of this theory for understanding psychiatric medications, tolerance effects, and the complexity of human biology. He concludes by discussing the strengths and potential weaknesses of the theory, noting that while it's an interesting perspective, it's too early to determine its full validity or impact. Shorter summary