Latent toxoplasmosis also slows a person’s reaction time, which may explain why multiple studies have found that infected people get into more car accidents. One prominent researcher speculated that toxoplasmosis indirectly kills a million drivers and pedestrians a year worldwide.
Another researcher summed up the personality patterns by saying that infected men are alley cats — in other words, loners and scrappy fighters — and infected women are sex kittens. A third scientist has hypothesized that the high prevalence of toxoplasmosis in certain countries, including France and Brazil, may influence cultural stereotypes about those nations.
That’s quite a lot to blame on a parasite.
Could other widespread microbes be covertly influencing our individual, or even national, characters? No one knows. The field is a blank slate.
But here’s a possibility to consider: Your body contains roughly 100 trillion cells, only one-tenth of which contain your DNA. The other 90 percent are bacteria. Your body, especially your gut, contains whole worlds of bacteria that live and eat and breed and die within you. Without them, we couldn’t survive; they make vitamins and nutrients that our bodies can’t manufacture on their own.
Last month, an international team of researchers published a detailed analysis of gut bacteria from several dozen people living in different countries. They found they could sort everyone into one of three categories based on which kinds of bacteria were most abundant. They also determined that one bacterial category, or enterotype, is more efficient at making folate, an important vitamin. Another enterotype is better at producing the vitamin riboflavin.
What other differences might exist between people as a consequence of the bacteria that live inside them? Could the microbes be influencing our brains? The discoverers of the three enterotypes didn’t evaluate personality traits, so for now we have no way of knowing.
But my gut would say it’s entirely possible.
Harder is general manager of health and science at U.S. News & World Report.