ERROL MORRIS: One other question occurred to me. Take these two smiles, the “say cheese” smile and the smile of genuine pleasure. Wouldn’t natural selection have built into our perceptual apparatus the ability to quickly discriminate between the two?

PAUL EKMAN: Well, it apparently hasn’t. One has to try reasoning backwards, “There must not have been any advantage to being able to tell the difference between the two.” The most important thing in terms of adaptation is for you to know that the other person is either actually or simulating enjoyment. And that was more important than whether they really were enjoying themselves. The fossil record doesn’t tell us much about social life. All one can do is to say there is no really good facial signal that evolved. Now when people laugh in a phony way, that’s a little easier to pick up. But even then, most of us want to hear good news. We don’t want to hear bad news. So we’re tuned to it. We’re very attracted to smiles. They’re very salient. But telling the feigned from the genuine, we’re not good at that for any emotion, for anger, fear. It takes quite a lot to train a professional, a National Security or law enforcement professional (we do quite a bit of that) to be able to distinguish between the two. There are no clear-cut obvious signs. So what must have been important was to know what a person was intending, not what they were feeling.

This is a pretty comprehensive essay about revisiting one of the more important photographs from Abu Ghraib. There is an impressive back story, and a lot of research here. "Standard Operating Procedure" looks to be intense, if this is the kind of work Morris is doing. Which is typical of Errol Morris, but still.

Long essay but worth it.