This might explain a few things.
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.