Comment by h2zizzle

GP's hypothesis is that diet/environment microbiome changes induce a protective social anxiety. However, a nomadic population - the most likely to exhibit those changes - are successful when exhibiting prosocial or confrontational characteristics, the opposite of social anxiety. Social anxiety is most protective for sedentary groups, who probably should be suspicious of outsiders.

Nothing you said contradicts this, and I'm not sure how to square the circle, even though microbiome-mediated behavior as an explanation for broad, otherwise irrational behavior patterns is attractive.