1. Presented by Sara Brinda
“Can the common brain parasite, Toxoplasma gondii, influence human culture?” by Kevin D. Lafferty
Presented by Sara Brinda

2. What is Toxoplasma gondii?
Protozoan parasite capable of infecting all endothermic vertebrates
Felines are primary hosts: only sexually reproductive in feline gut epithelium, disperses through oocytes in feces
Remains alive in soil for up to a year, consumed by cats and other hosts
If they are consumed by intermediate (secondary) hosts, parasites are under selection to increase the chance that primary (definitive) hosts eat intermediate hosts (allowing them to re-enter their primary hosts)
T. gondii alter the behavior of intermediate hosts to increase predation risk
Webster, 2001

3. “Could aspects of human culture result from a parasite selected to predispose its host to predation by cats?”

4. How does T. gondii affect behavior of rodents?
Infected rodents are: more active, first to enter traps, less fearful of cats and associated smells
Mechanism in brain = elevates dopamine, which is known to alter novelty-seeking and neuroticism

5. Does T. gondii affect people?
YES, it modifies the behavior even of “dead end” hosts
People can ingest infected soil, or infected meat
Mild flu-like symptoms initially, then the parasite becomes dormant in the brain (or other tissues)
Mechanism in brain = unknown; speculated to also be elevated dopamine levels caused by altered cytokine levels (brain’s local immune response against T. gondii)
WHY? “T. gondii has nothing to lose evolutionarily speaking, in trying manipulative strategies in other host species.”
Long-term personality changes
Webster, 2001

6. Goals of study
To determine whether aggregate personalities of cultures are affected by T. gondii
Whether prevalence of T. gondii infection could explain variation in cultural dimensions among human populations

7. Methods Collected data on infection prevalence in different countries
Women of childbearing age
Correct for countries with older mothers
Collected data on relevant population-level personality: neuroticism (affected by guilt-proneness), uncertainty avoidance, and culturally “masculine” sex roles
Performed General Linear Model to test for correlation between aggregate neuroticism, uncertainty avoidance, and masculinity

9. Results

10. Factors determining infection prevalence
Climate
Dwelling among cats
Working with soil/poor hygeine
Cuisine including rare or undercooked meats

11. What are the societal implications?
Extremely widespread parasite explains some aspects of individual personality
Also may explain a small part of two (sex roles, uncertainty avoidance) of the four principal cultural dimensions (others = individualism, class distinction)
Could have medical or economic implications

12. What if we did not recognize evolution?
We would not understand anything about this parasite!
The selection pressures that led to its ability to manipulate behavior
Its non-adaptive behavior in human hosts (kind of a correlated character, a “side-effect of prior selection in intermediate hosts…it is unlikely that any parasite would have the recognition and modulatory mechanisms able to restrict expression to within only those hosts likely to be predated.”)

13. References FOCAL PAPER:
Lafferty, Kevin D.. "Can the common brain parasite, Toxoplasma gondii, influence human culture?." Proceedings of the Royal Society B: Biological Sciences 273(2006):
ADDITIONAL SOURCE:
Webster, Joanne P.. "Rats, cats, people and parasites: the impact of latent toxoplasmosis on behaviour." Microbes and Infection 3(2001):
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