We may have inadvertently selected for muscles on dogs’ faces

Enlarge / A muscle flex raises the inner portions of the eyebrow at right. (credit: Waller et al.)
Humans domesticated dogs about 30,000 years ago. Since then, we've worked with them, hunted with them, played with them, and come to rely on them for companionship. And, in the process, we've bred them for everything from general cuteness to the ability to guard and fight for us. Figuring out who's manipulating whom and who's getting more out of the relationship is a hopeless task.
But that doesn't mean that some aspects of the changes dogs have undergone aren't amenable to study. After studying the facial muscles of dogs and wolves, a US-UK team of researchers has now found that dogs have two muscles that wolves mostly lack. These muscles control the movements of the face near the eyes, and the researchers suspect that the muscles' presence helps the dogs make a sad-eyed face that we find appealing.
A “take me home” look
The new work arose from an earlier paper done by several of the same researchers (Juliane Kaminski, Bridget Waller, and Anne Burrows). In it, they looked at what's technically called a 'paedomorphic facial expression' in dogs. Paedomorphic means that adults retain features that are commonly associated with young animals—we tend to view these as cuter. In this case, the expression was raising the skin above the eyes, closer to the bridge of the nose. This expression, shown above, has been interpreted as 'sad-eyed' and is thought to tug on humans' heart strings.
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