"German Shepherd Dogs" by jn2race / CC BY-SA 2.0

Domestication Made Dogs’ Facial Anatomy More Fetching to Humans

Jun 18, 2019

By Jim Daley

In the celebrated Claymation series Wallace and Gromit, loyal dog Gromit is silent yet highly expressive, often making his thoughts known with pronounced eyebrow movements. Although they are exaggerated on the clay pup for comedic effect, any real dog’s owner will confirm these animals do seem to have highly communicative faces. A pooch’s raised eyebrows and tilted head suggest meaning to humans, and widened “puppy dog eyes” endear our pets to us. Researchers reported Monday in Proceedings of the National Academy of Sciences that our best animal friend’s facial anatomy may have evolved specifically for that purpose as a result of human selection.

The new study combined anatomical and behavioral experiments. The scientists first compared the facial anatomy of six domestic dogs, each representing a different breed, to that of four gray wolves (modern dogs’ closest living relatives) from two wild populations. They found that the muscles required to raise the inner eyebrows and widen the eyes are present in most dogs—but not in wolves, which have a small tendon instead. Next the researchers exposed nine wolves and 27 dogs to humans for two minutes, and observed the canines’ behavior. The dogs, but not the wolves, made the “highest intensity” eyebrow movements while in the humans’ presence. The researchers surmise that dogs gradually developed the anatomy underlying this communicative ability in response to human preference across tens of thousands of years.

Bridget Waller, an evolutionary psychologist at the University of Portsmouth in the U.K., and co-author of the study, says interspecies communication is an important evolutionary adaptation in some domesticated animals—largely because it has such a high priority among humans. “Communication is key to everything that we do with each other,” Waller says. When humans domesticated animals, “we shaped them into things that we can relate to and that are useful to our lives.” This process likely occurred both on conscious and unconscious levels. Humans actively selected for certain traits because they helped make animals more useful as laborers or food sources, Waller explains. Other attributes—such as more expressive faces—may have simply made animals more tolerable to humans so we were more likely to care for them, she says, “even if we were not intending to create a new behavior or new morphological trait.”

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