This article studies a famous unsolved puzzle in quantitative social science. Why do some nations report such high levels of mental well-being? Denmark, for instance, regularly tops the league table of rich countries’ happiness; Britain and the US enter further down; some nations do unexpectedly poorly. The explanation for the long-observed ranking – one that holds after adjustment for GDP and other socioeconomic variables – is currently unknown. Using data on 131 countries, the article cautiously explores a new approach. It documents three forms of evidence consistent with the hypothesis that some nations may have a genetic advantage in well-being.