Cat parasite may affect cultural traits in human populations

A common parasite found in cats may be affecting human behavior on a mass scale, according to a scientist based at the University of California, Santa Barbara.

While little is known about the causes of cultural change, and biological explanations often stimulate social and scientific debate, a new study by the U.S. Geological Survey published in the August 2 issue of the Proceedings of the Royal Society, Biology, indicates that behavioral manipulation of a common brain parasite may be among factors that play a role.

“In populations where this parasite is very common, mass personality modification could result in cultural change,” said study author Kevin Lafferty, a USGS scientist at UC Santa Barbara. “The geographic variation in the latent prevalence of Toxoplasma gondii may explain a substantial proportion of human population differences we see in cultural aspects that relate to ego, money, material possessions, work and rules.”

Although this sounds like science fiction, it is a logical outcome of how natural selection leads to effective strategies for parasites to get from host to host, said Lafferty. Toxoplasma gondii is a parasite of cats, both domestic and wild. While modern humans are a dead-end host for the parasite, Toxoplasma appears to manipulate personality by the same adaptations that normally help it complete its life cycle. The typical journey of the parasite involves a cat and its prey, starting as eggs shed in an infected cat’s feces, inadvertently eaten by a warm-blooded animal, such as a rat. The infected rat’s behavior alters so that it becomes more active, less cautious and more likely to be eaten by a cat, where the parasite completes its life cycle. Many other warm-blooded vertebrates may be infected by this pathogen. After producing usually mild flu-like symptoms in humans, the parasite tends to remain in a dormant state in the brain and other tissues.

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