Awesome science,part IX (?): hypermasculinity is a sickness

Approximately one-quarter of Americans host a parasite that has been shown to affect personality in both rodents and humans. According to a recent study, this single-celled organism may be able to shape entire cultures.

In a paper published in the online edition of Proceedings of the Royal Society, United States Geological Survey researcher Kevin Lafferty argues that a significant factor in why some countries exhibit higher levels of neuroticism than others may be the prevalence of the parasite Toxoplasma gondii. The study also indicates that it may influence a society's preference for strict laws, an expression of uncertainty avoidance, and its valuation of 'masculine' priorities such as competitiveness and financial success over 'feminine' values like relationship-building.

"Toxoplasma appears to explain 30% of the variation in neuroticism among countries, 15% of the uncertainty avoidance among Western nations and 30% of the sex role differences among Western nations," Lafferty said via e-mail.
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Infected men tended to have lower levels of intelligence, superego strength and novelty-seeking, while infected women exhibited higher levels of intelligence, superego strength and warmth. Infected people of both sexes tend to be susceptible to feelings of guilt.

Make your own jokes about, you know, people who might start unnecessary wars to sort out their daddy issues.

Seed article. Original journal abstract.

UPDATE:

In response to Solomon's and my girlfriend's sputtering questions (his in the comments below, hers over the phone), I did a little internet research and now bring you the following information. First, what is Toxoplasma?

Toxoplasmosis results from infection by the parasite Toxoplasma gondii. Most domestic cats are or will be infected during their lives. The parasite reproduces within cats but is passed through their feces to intermediate hosts, particularly rats and humans. The parasites spread through the body, lodging primarily within the muscle and brain tissue, where they will remain throughout the host's life. When a cat eats an infected rat or bird or uncooked meat, the cat acquires the parasite, and the cycle continues. The rate of infection in humans ranges from 20%-80%, varying by country with France at the high end. Billions of people thus have parasites in their brains.
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Toxoplasma gondii has been shown to affect the behavior of infected rats, who exhibit slower reaction times, reduced fear response, and a fatal attraction to cat scent. This last was demonstrated in a convincing paper [link via Future Pundit] by Berdoy, Webster, and Macdonald. They used rat, rabbit, and neutral scents as control for the cat scent and watched rats' foraging behavior over hundreds of hours under laboratory conditions. (I might have done the statistical analysis a bit differently, but their model and analysis are commonly used for this kind of data and should work well.) Berdoy et al. found that infected rats showed a stable preference for cat smells whereas uninfected [r]ats strongly avoided them.

CDC factsheet here. The quote above is from a mostly negative appraisal of Jaroslav Flegr's work by Carnegie Mellon University Professor of Statistics Christopher Genovese. Jaroslav Flegr is a Czech scientist who has investigated the behavior-altering properties of Toxoplasma in humans, using a common, 16-dimension survey to assess personality in infected and uninfected people. See some of his papers here and here. I got those links from Genovese, who links to many more. From the second link, here's a representative finding.

Two hundred and twenty-four men and one hundred and seventy women were tested for toxoplasmosis and their personality profiles were measured by Cattell's questionnaire. Highly significant differences between Toxoplasma infected and uninfected subjects were observed (p < 0.01). For men the factors G (low superego strength [disregards rules, expedient], p<0.02), and possibly L (protension [suspecting, jealous, dogmatic]), O (guilt proneness), and A (sizothymia [reserved, detached, critical) prevailed in infected subjects. For women the prevailing factors were A (affectothymia [warmhearted, outgoing, easygoing], p<0.01), and possibly L (alaxia [trusting, accepting conditions, tolerant]) and N (shrewdness). To reveal whether toxoplasmosis induces personality factor-shifts or whether certain combinations of personality factors influence the probability of acquiring Toxoplasma infection, we examined the personality profiles of 164 male patients diagnosed with acute toxoplasmosis during the past 13 years. The existence of a positive correlation between the duration of latent toxoplasmosis and the intensity of superego strength decrease (p<0.02) suggested that the decrease of superego strength (the willingness to accept group moral standards) was induced by T. gondii infection.

Flegr has also found that Toxoplasma infection slows reaction times, which he suggests may lead to increased risk of traffic accidents (both links PDFs).

Most amusing is this characterization FuturePundit lifts from a London Times article no longer available online for free.

[W]omen infected with toxoplasma spent more money on clothes and were consistently rated as more attractive. “We found they were more easy-going, more warm-hearted, had more friends and cared more about how they looked,” he said. “However, they were also less trustworthy and had more relationships with men.”

By contrast, the infected men appeared to suffer from the “alley cat” effect: becoming less well groomed undesirable loners who were more willing to fight. They were more likely to be suspicious and jealous. “They tended to dislike following rules,” Flegr said.

What Lafferty seems to have done is take preexisting country-level data on rates of Toxoplasma infection and personality scores in that same survey Flegr used, and analyzed them to see how they match up. "Neuroticism" appears to be a technical description related to some of the trait dimensions in the personality survey.