New research indicates that social conservatism can help explain the negative correlation between religiosity and cognitive abilities.

There exists a cluster of psychological traits and attitudes that have been described as the “conservative syndrome.” The term isn’t meant to describe conservatism as a disease. Rather, “syndrome” denotes that a number of traits and dispositions associated with conservatism are correlated with each other.

The new study, published in Personality and Individual Differences, suggests that the “conservative syndrome” is associated with lower intelligence, and religiosity is only a part of it.

“It should understand that social conservatives, including very religious people, tend to be more restricted in their views of the world,” Stankov told PsyPost. “Because of their lower IQ they are more close-minded and afraid of change. They also tend to be more nasty towards those who do not belong to their own group.”

Oh no - it gets worse:

 A defining trend in human intelligence tests that saw people steadily obtaining higher IQ scores through the 20th century has abruptly ended, a new study shows.
The Flynn effect – named after the work of Kiwi intelligence researcher James Flynn – observed rapid rises in intelligence quotient at a rate of about 3 IQ points per decade in the 20th century, but new research suggests these heady boom days are long gone.
An analysis of some 730,000 IQ test results by researchers from the Ragnar Frisch Centre for Economic Research in Norway reveals the Flynn effect hit its peak for people born during the mid-1970s, and has significantly declined ever since.
What the results show is that a turning point for the Flynn effect occurred for the post-1975 birth cohorts, equivalent to 7 fewer IQ score points per generation.