I like the way you asked a question there.

• Studies linking common traits related to interaction with authorities with respect to beliefs.
• High correlation of extraversion with conformist thinking
• Relevance of both of the above to tendencies toward prioritising epistemic rationality.
• Game theoretic incentives for adopting certain signalling strategies based off various social niches.
• IQ: relevant.
• Big Five: even more relevant. Openness to experience in particular. Extraversion is relevant via the previous mentioned conformist tendencies.
• It's about personality. Personality is overwhelmingly dominated by genetic factors.
• Have you seen the children of engineers and scientists? Seriously, how is this not obvious?
• Epistemic rationality is basically a mental defect. Sure, maybe not in existential terms. But certainly in the "He who dies with the most toys wins (and probably got laid more)" sense. Thinking rationally just isn't much of a recipe for conventional success. Vulnerability to overemphasising abstract thought over primate political thought is rather closely related to tendencies towards Asperger's. And even at the sub-diagnostic level nerds that breed are more likely to produce offspring that are diagnosable. Somewhere along that spectrum there is a maximum likelyhood of catching rationalism.
• Rational thinking is nerdy. Nerdiness is heritable.