Evolution of facial muscle anatomy in dogs.

Evolution of facial muscle anatomy in dogs.
Dogs have been shaped during the course of domestication both in their behavior and in their anatomical features. Here we show that domestication transformed the facial muscle anatomy of dogs specifically for facial communication with humans. A muscle responsible for the intense elevation of the inner eyebrow is uniformly present in dogs, but not in wolves. Behavioral data show that dogs also produce the eyebrow movement significantly more frequently and with greater intensity than wolves, with higher intensity movements produced exclusively by dogs. Interestingly, this movement enhances pedomorphism and resembles an expression that humans produce when they are sad, so its production in dogs may trigger a caring response. Our hypothesis is that the expressive eyebrows of dogs are the result of selection based on the preferences of humans.
Recent research suggests that eye contact between humans and dogs is crucial for dog-human social interaction. Dogs, but not wolves, make eye contact with humans when they cannot solve a problem on their own Eye contact also helps dogs know when communication is relevant and directed at them, because dogs tend to ignore human pointing gestures when human eyes are not visible.
Thus, the mutual gaze between dogs and humans seems to be a hallmark of the unique relationship between both species during human cultural evolution.