The overlapping geography of cognitive ability and chronotype

Chronotype and cognitive ability are two psychological phenotypes with an uneven geographical distribution due to both selective migration and causal environmental effects. In our study we aimed to unravel the relationship between geographical variables, cognitive ability and chronotype. We used a large anonymized sample (N=25700) of dating site users to estimate chronotype and cognitive ability from questionnaire responses using item response theory. We matched each user to geographical coordinates and city size using the reported locations and geographical databases. In line with previous research we found that male sex (β=0.029), younger age (β=-0.178), residence in a more populous locale (β=0.02), higher cognitive ability (β=0.05) and more westward position within the same time zone (β=-0.04) was associated with later chronotype. Male sex (β=0.065), younger age (β=-0.04), residence in a more populous locale (β=0.149), later chronotype (β=0.051) and higher latitude (β=0.03) was associated with higher cognitive ability, but the effect of population on chronotype and latitude on cognitive ability was only present in the United States. The relationship between age and chronotype was stronger in males, and the relationship between chronotype and cognitive ability was stronger in males and in older participants. Population density had an independent association with cognitive ability, but not chronotype. Our results confirm the uneven geographical distribution of chronotype and cognitive ability. Country-wise analyses distinguish universal cultural/biological and country-specific effects. The moderating effect of age on the cognitive ability-chronotype relationship suggests that cultural rather than biological effects underlie this relationship.