In 110 years, Americans went from saying ‘prunes’ to ‘cheese’ for the yearbooks

We’re all smiling more widely now, showing more of our teeth, being more unrestrained about expressing emotion.

Those are the results of assessing 110 years of American high school yearbook photos. Click here to get to the research conducted by Shiry Ginosar at the University of California, Berkeley, and some others. They call it ‘A Century of Portraits: A Visual Historical Record of American High School Yearbooks’.

The research started with a vast unmined database of yearbook photographs dating back to 1905 showing full frontal shots of girls and boys in a standard pose. The team downloaded more than 150,000, removed those that weren’t full frontal and then studied the remaining 37,000 images from more than 800 yearbooks from 26 US states.

As this Technology Review piece describes it, “They then grouped the portraits by decade and superimposed the images to produce an ‘average’ face for each period.” This basically meant the “average” features – for hairstyle, clothing, style of glasses and facial expressions – for each decade for men and women.

(That has many interesting elements too. In the 1930s, hair was all about finger waves; in the 40s and 50s, pin curls; in the 60s, there was the bob, ‘winged’  flip and bubble cut; the 70s had long hair, Afros, and bouffants; the 80s and 90s perms and bangs and in the 2000s it’s been straight long hair.)

Crucially, they found that smiling had changed. Immediately after the invention of photography, says the team, most people adopted the same pose for the yearbook as they would have used for a painted portrait. “Etiquette and beauty standards dictated that the mouth be kept small — resulting in an instruction to ‘say prunes’ (rather than cheese) when a photograph was being taken,” they write.

During the 20th century they were smiling, especially after Kodak’s advertisements popularized the idea of recording happy memories.

“These days we take for granted that we should smile when our picture is being taken,” they write.

Technology Review says the Ginosar team developed an algorithm for determining the degree of lip curvature in the photographs and this showed a clear trend in increasing smile intensity over time.

The point about this study is that it spotted a trend relatively easily and quickly by using a big digitised data collection and an algorithm, something that would in the past have only been done through the manual analysis of thousands of photos.

Enough to smile about. Very widely.