Editor’s Note: This article previously appeared in a different format as part of The Atlantic’s Notes section, retired in 2021.

If you haven’t seen this Atlantic video already, Sam Kean, author The Tale of the Dueling Neurosurgeons, provides a multi-faceted answer to the question:

But what about child artists?

Kids haven’t been exposed to adult paintings, museum art, cultural cues — they just grab crayons and draw. Do they draw faces looking left? They do, says Sam. Most kids — especially the righties — draw people facing left. “Overall culture probably influences the direction of portraits somewhat,” he wrote, “but most artists naturally highlight the left side.”

But there are exceptions to this general rule:

Leonardo da Vinci, who painted Mona Lisa, often went the other way and produced lots of right-facing portraits. Self-portraits, it seems, often face right. But, Sam says, “Artists tend to paint self-portraits in the mirror, which makes the left half of the face appear on the right side of the canvas. So this ‘exception’ might actually confirm the bias.”

One reader isn’t satisfied by Sam’s explanation in the video:

Do you really think people study their faces to discover which side is more expressive? I don’t. Or do we instinctively know which side is “better”? Again, I doubt it. I think it has more to do with sight. We’re not turning to expose the left side of the face, we are looking off to the right. Why this should be so, I have no idea, but it just seems the simpler and more natural explanation.

Why would artists show people this way? Most often, they work with live models, and in instructing them, I think they would naturally look to the right and say, “Do this,” or something along those lines.

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