Look at a person's photo and it's tempting to think you can see their personality written all over it: stony-faced individuals appear sombre; others flashing a big, toothy grin seem more genial. An intriguing new study claims that these smiles are a reliable marker of underlying positive emotion and as such are predictive of a person's longevity.
Ernest Abel and Michael Kruger had five people rate the smile intensity of 230 baseball players according to photos featured in the 1952 Baseball Register. The researchers used a three-point smile scale: no smile, half smile (mouth only), and genuine 'Duchenne' smile (muscles contracted around the mouth and corners of the eyes).
Focusing on the 150 players who'd died by the time of the study and controlling for extraneous factors such as BMI and marital status, the researchers found that those who were flashing a genuine 'Duchenne Smile' were half as likely to die in any given year compared with non-smilers. Indeed, the average life-span of the 63 deceased non-smilers was 72.9 years compared with 75 years for the 64 partial smilers and 79.9 years for the 23 Duchenne smilers.
A follow-up study was similar to the first but observers rated the attractiveness of the same players rather than their smile intensity. Unlike smile intensity, attractiveness bore no relation to longevity.
'To the extent that smile intensity reflects an underlying emotional disposition, the results of this study are congruent with those of other studies demonstrating that emotions have a positive relationship with mental health, physical health, and longevity,' the researchers said.
Abel, E., & Kruger, M. (2010). Smile Intensity in Photographs Predicts Longevity. Psychological Science DOI: 10.1177/0956797610363775