It seems so obvious that someone should have thought of it decades ago: Since parasites have plagued eukaryotic life for millions of years, their prevalence likely affected evolution. Psychologist Marco Del Giudice of the University of New Mexico is not the first researcher to suggest that the evolution of the human brain could have been influenced by parasites.
The point is that parasites are really bad for hosts, and it therefore stands to reason that the evolution of modern humans includes protective countermeasures that were selected for success and likely shaped the stupefyingly complex central nervous system.
The paper is organized by four countermeasures hosts have evolved against manipulative parasites: restricting access to the brain; increasing the costs of manipulation; increasing the complexity of signaling; and increasing robustness.
Del Giudice includes in the paper a discussion of the constraints on the evolution of countermeasures by hosts. These include metabolic and computational constraints such as energy availability and small body size—animals with larger brains can more easily evolve higher levels of protective complexity. This is one reason that behavior-altering parasites are more commonly observed in insects, which have provided fundamental examples of parasite strategies and host countermeasures.
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