“… the degree to which one smiles in photographs taken in early life predicts the likelihood that a person will be divorced later in life.” say researchers from the Touch and Emotion Lab at DePauw University, Greencastle, Indiana, US, a key center for facial and tactile communication studies. The lab has recently completed two long-term investigations which retrieved and examined early photographs of more than 400 participants – and then correlated the degree to which the subjects  were smiling in the pictures with the incidence of divorce in later life.
Although there are several plausible theories regarding possible underlying sociological and/or psychological mechanisms, there is as yet no proven explanation for this enigmatic effect:

“…our data do not reveal the specific process(es) that may account for the relation between smiling in early life and divorce.”

The study was published in the June 2009 issue of the journal Motivation and Emotion.    A full copy may be found here:

Supporting material. One of the most famous smiles in recent Western history, belonging to Lisa di Antonio Maria (Antonmaria) Gherardini, who was not, as far as is known, divorced.