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Can the common brain parasite, Toxoplasma
gondii, influence human culture? by Kevin D.
Lafferty

• Presented by Sara Brinda

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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
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• Could aspects of human culture result from a
  parasite selected to predispose its host to
  predation by cats?

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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

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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 (brains 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
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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

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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

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Results
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Factors determining infection prevalence

• Climate
• Dwelling among cats
• Working with soil/poor hygeine
• Cuisine including rare or undercooked meats

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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

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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 hostsit 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.)

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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) 2749-2755.
• ADDITIONAL SOURCE
• Webster, Joanne P.. "Rats, cats, people and
  parasites the impact of latent toxoplasmosis on
  behaviour." Microbes and Infection 3(2001)
  1037-1045.
• Also
• http//www.cuteoverload.com
• http//www.cricava.com