We've bred dogs to have expressive eyebrows that manipulate our emotions
Dogs have muscles that control their eyebrows that don't exist in wolves
Researchers have found that the puppy dog eyes that humans find so irresistible are made possible by muscles that have evolved in dogs since they separated from wolves. They think this was likely a result of selection by human breeders who to enable better communication with our furry friends.
Dogs can raise their inner eyebrows, which makes their eyes appear larger and gives them a forlorn look that humans read as sadness. According to a new study by Anne Burrows, a professor of anatomy at Duquesne University in Pittsburgh, it's a look humans often find irresistible, and dogs may know this and use it to their advantage.
If you've got 'em, flaunt 'em — eyebrows that is
Burrows led a study five years ago that found the dogs in a shelter with the most expressive eyebrows were the ones that found new homes fastest.
Previous research had shown that a dog's ability to make eye contact with humans made them easier to direct and therefore perhaps made them more capable hunting companions. An ability to produce pleasing facial expressions might also have helped with this. This suggests to researchers that human preference for certain kinds of facial anatomy might have had a big influence on the way their faces evolved over the 30,000 years that they've been human companions.
Dog and wolf eyebrows
In Burrows' most recent study, she looked at the facial anatomy and behaviour of dog eyebrows and compared it to that of the wolf. Dogs and wolves had similar facial anatomy around the mouth and ears, but not the eyes.
Most modern breeds of dog have have the well-developed facial muscles that makes raising eyebrows possible. In wolves however, only a few fibres of that same muscle exist.
Burrows and her team also observed that dogs were found to raise their inner eyebrows more frequently and at a higher intensity when in the presence of a human. They don't know yet whether dogs also make these expressions around other dogs as well.
Dogs use their eyebrows against us
That fact that humans selected for dogs with expressive eyebrows really means that we are responsible for they way they manipulate us with their puppy eyes. It's consistent with other ways we've selected for dogs to appear different from wolves, including shorter snouts and smaller teeth.
Both characteristics suggest non-aggressive appearance and behaviour that contributed to the domestication of dogs over time.
As for the question of whether dogs are aware that the can use their puppy dog expression to gain our favour, Burrow suggests that her own dog certainly does, especially close to dinnertime.