Excerpted from http://notexactlyrocketscience.wordpress.com/2007/01/14/brain-parasite-drives-human-culture/
Kevin Lafferty from the University of California, Santa Barbara, has found startling evidence that a common brain parasite, Toxoplasma gondii, could be influencing human culture across the globe.
Toxoplasma gondii is a single-celled brain parasite spread by cats. Our feline companions are its preferred home and only there can it mature and reproduce. So like most parasites, T.gondii has a complex life cycle designed to get it into its final host.
If it finds itself in another animal, it travels to the brain and changes the host’s behaviour to maximise its chances of ending up in a cat. For rodents, this means being eaten and infected individuals are less fearful of cats and more active, making them easier prey.
Humans can also contract the parasite, through contact with soil contaminated by the faeces of carriers or through eating infected meat. But since cats are very unlikely to eat humans, in our bodies, T.gondii reaches a cul-de-sac. Still, there is nothing to stop the parasite, evolutionarily speaking, from trying out the strategies that work so well in other hosts.
In rare cases, T.gondii infection causes a disease called toxoplasmosis that produces mild flu-like symptoms and only really threatens foetuses and those with weak immune systems. In most instances, the parasite acts more subtly.
Carriers tend to show long-term personality changes. Women tend to be more intelligent, affectionate, social and more likely to stick to rules. Men on the other hand tend to be less intelligent, but are more loyal, frugal and mild-tempered. The one trait that carriers of both genders share is a higher level of neuroticism – they are more prone to guilt, self-doubt and insecurity.
In individuals cases, these effects may seem quirky or even charming but across populations, they can have a global power. T.gondii infection is extremely common and rates vary greatly from country to country.
While only 7% of Brits carry the parasite, a much larger 67% of Brazilians are infected. Given that the parasite alters behaviour, infection on this scale could lead to sizeable differences in the general personalities of people of different nationalities. This is exactly what Lafferty found.
Neuroticism is one of the most widely-studied of all psychological traits and Lafferty found that levels in different countries correlated well with the levels of T.gondii infection. The parasites’ presence was also related to aspects of culture associated with neuroticism.