Cute by Design: A Scientific Explanation for the Puppy Dog Face

Researcher Juliane Kaminski and team at Duke University recently found seemingly conclusive data that the ‘puppy dog face’ is an evolutionary byproduct of human enforced selection.

Through a comparative physiological study of musculature in wolf and dog heads, it was shown that the levator anguli oculi medialis, “a muscle responsible for raising the inner eyebrow intensely”, was found to be, “uniformly present in dogs but not in wolves. Behavioral data, collected from dogs and wolves, show that dogs produce the eyebrow movement significantly more often and with higher intensity than wolves do, with highest-intensity movements produced exclusively by dogs.”

Comparing this physiological study of musculature with a behavioral study of artificial selection processes in dog shelters, a team at the University of Sydney,  found that dogs with musculature better equipped to make the puppy face were selected as pets at much higher rates:

“Using the speed of selection from rehoming shelters as a proxy for artificial selection, we tested whether paedomorphic features give dogs a selective advantage in their current environment. Dogs who exhibited facial expressions that enhance their neonatal appearance were preferentially selected by humans.”

Humans, it is then claimed, exploited this muscle, conditioning it as a preferential evolutionary path – not surprising.

Domesticity and Paedomorphism by Design

Using these two studies, researchers have made a number of educated guesses about the secret history of dog domestication. As argued by Waller and team:

"One hypothesis suggests that wolves underwent a process of self-domestication as tamer individuals took advantage of opportunities to scavenge from human settlements during the agricultural revolution. In support of this theory is recent evidence that domestic dogs exhibit genetic mutations to a starch-rich diet. During domestication, dogs have departed from wolves on various other behavioral and physical dimensions, one of the most striking being paedomorphism. In many ways dogs appear more like wolf puppies than wolf adults."

Waller’s hypothesis would then not only give us clues about the secret history of domestication but also could tell us something about the science of cuteness – what scientists are calling paedomorphism: the retaining of infant-like features in maturity.

Scientists have likened it to juvenile characteristics, which humans find attractive and unthreatening.

As Waller goes on to state about the case of dogs:

“Interestingly, this movement increases paedomorphism and resembles an expression that humans produce when sad, so its production in dogs may trigger a nurturing response in humans.”

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Human attraction to paedomorphic character traits is also evident in domestic cats.

As Karen McComb has found in a study on the ‘purr’ sound, these vocalizations are associated with the cries of a human infant and hence elicit empathy. The empathy delivered may have been a key to the cats entrance into our hearts and homes over the centuries. Like the dogs' sadness, the paedomorphic characters of the cat are what keeps them close – odd.

Here we have it, a scientific explanation for something as intimate and seemingly preferential as ‘cuteness’.

It leaves the question of who is in control? Perhaps we are on a different side of the leash than we imagine.