Within families, a sibling with a higher IQ or more favorable polygenic scores for intelligence was more likely to lean towards liberal political beliefs compared to their sibling. This was consistent across both biological and adoptive families.
This outcome underscores the potential genetic underpinnings of political ideology, suggesting that the variation in genetic factors related to intelligence could partially explain why siblings raised in the same environment might develop diverging political views.
“We find both IQ and genetic indicators of intelligence, known as polygenic scores, can help predict which of two siblings tends to be more liberal,” Edwards told PsyPost. “These are siblings with the same upbringing, who are raised under the same roof. This implies that intelligence is associated with political beliefs, not solely because of environment or upbringing, but rather that the genetic variation for intelligence may play a part in influencing our political differences. Why is this the case? I do not know.”
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