Sunshine on my shoulders makes me happy. . . especially if I’m less intelligent: how sunlight and intelligence affect happiness in modern society

ABSTRACT

The savanna theory of happiness proposes that, due to evolutionary constraints on the human brain, situations and circumstances that would have increased our ancestors’ happiness may still increase our happiness today, and those that would have decreased their happiness then may still decrease ours today. It further proposes that, because general intelligence evolved to solve evolutionarily novel problems, this tendency may be stronger among less intelligent individuals. Because humans are a diurnal species that cannot see in the dark, darkness always represented danger to our ancestors and may still decrease our happiness today. Consistent with this prediction, the analysis of the National Longitudinal Study of Adolescent to Adult Health (Add Health) data shows that exposure to sunlight was associated with happiness but the association was significantly weaker among more intelligent individuals.

Keyword:

• Seasonal affective disorder (SAD)
• subjective well-being
• life satisfaction

Data availability statement

Certified researchers may obtain replication data and materials from the Carolina Population Centre by contacting [email protected] and signing a limited, one-year, no-fee contract for replication purposes only.

Disclosure statement

The authors declare absolutely no conflict of interest, real or perceived.

Notes

1 Add Health Wave IV measures the frequency of nine other positive and negative emotional states in the last seven days on the same scale: “You were bothered by things that usually don’t bother you,” “You could not shake off the blues, even with help from your family and your friends,” “You felt you were just as good as other people,” “You had trouble keeping your mind on what you were doing,” “You felt depressed,” “You felt that you were too tired to do things,” “You enjoyed life,” “You felt sad,” “You felt that people disliked you.” The measure of happiness was significantly and very strongly correlated with all nine measures of positive and negative emotions in the expected directions (bothered: r = -.317; blues: r = -.430; self-respect: r = .441; distracted: r = -.277; depressed: r = -.495; tired: r = -.232, enjoyed life: r = .743; sad: r = -.477; disliked: r = -.244). It therefore appears to be a valid measure of positive, eudemonic state. Previous studies show that single-item measures of happiness are extremely valid and correlate highly with multi-item batteries such as the Oxford Happiness Inventory and the Satisfaction with Life Scale (Abdel-Khalek, 2006; Cheung & Lucas, 2014).

2 In generalised linear models (like ordinal regression that we employed here), the independent variables have proportional effects on the dependent variable in its natural unit and constant effects on the logit (natural log of odds of a respondent being in one category of the dependent variable versus another). As a result, simple slope analysis, of the kind typically conducted for OLS regression, cannot be performed on raw dependent variable and must instead be performed on the logit. Because the logit has no intuitive or readily interpretable meaning, we have chosen not to perform a simple slope analysis.