Cat Parasite Affects Everything We Feel and Do

Kevin Lafferty is a smart, cautious, thoughtful scientist who doesn't hate cats, but he has put forth a provocative theory that suggests that a clever cat parasite may alter human cultures on a massive scale.

Researchers say a cat parasite could be responsible for all kinds of human behavior and qualities. Here, an Abyssinian cat participates in a beauty contest in Bucharest, Romania, on April 26, 2009.

(Vadim Ghirda/AP Photo)

His phone hasn't stopped ringing since he published one of the strangest research papers to come out of the mill in quite awhile.

The parasite, Toxoplasma gondii, has been transmitted indirectly from cats to roughly half the people on the planet, and it has been shown to affect human personalities in different ways.

Research has shown that women who are infected with the parasite tend to be warm, outgoing and attentive to others, while infected men tend to be less intelligent and probably a bit boring. But both men and women who are infected are more prone to feeling guilty and insecure.

Other researchers have linked the parasite to schizophrenia. In an adult, the symptoms are like a mild form of flu, but it can be much more serious in an infant or fetus. Oxford University researchers believe high levels of the parasite leads to hyperactivity and lower IQs in children.

Lafferty, who is a parasite ecologist with the U.S. Geological Survey at the University of California at Santa Barbara, is an expert on the role parasites play in the ecology of other animals.

Building on research by scientists in the Czech Republic, Lafferty took a long look at areas of the globe where infection levels are quite high, or quite low. In Brazil, for example, two out of three women of child-bearing age are infected, whereas in the United States the number is only one out of eight.

Lafferty argues in a research paper published Aug. 2 in the Proceedings of the Royal Society, Biology, that aggregate personality types, or what cultures tend to be like, fit neatly with the effects that the parasite produces in individuals.

So that led to a basic question:

Can a common cat parasite account for part -- even if only a very small part -- of the cultural differences seen around the world?