There currently are 7.9 billion human faces on the planet. All are variations on the same template: two eyes flanking a nose above a mouth. Yet with a mere glance, most of us can tell the difference between any two faces. How do our brains make these lightning-fast judgments?
Spoiler alert: No one knows. And although computer programs today are excellent at putting names to faces, none is particularly good at judging just how similar (or dissimilar) different faces appear. But in a study published today in the Proceedings of the National Academy of Sciences (PNAS), an
