Toxoplasmosis seems to increase IQ test results in rh negative individuals

ADDED:

For an update see the article High IQ differences between rh- and rh+ with and w/out Toxoplasmosis

According to Toxoplasmosis-Associated Difference in Intelligence and Personality in Men Depends on Their Rhesus Blood Group but Not ABO Blood Group:

Here, we searched for differences in the toxoplasmosis-associated effects between RhD-positive and RhD-negative subjects by testing 502 soldiers with two personality tests and two intelligence tests. The infected subjects expressed lower levels of all potentially pathognomic factors measured with the N-70 questionnaire and in neurasthenia measured with NEO-PI-R. The RhD-positive, Toxoplasma-infected subjects expressed lower while RhD-negative, Toxoplasma-infected subjects expressed higher intelligence than their Toxoplasma-free peers. The observed Toxoplasma-associated differences were always larger in RhD-negative than in RhD-positive subjects.

Up to half of the world’s population is infected by toxoplasmosis but have no symptoms. In the United States about 23% are affected and in some areas of the world this is up to 95%.

Discussed in more detail here …