So the team tested dog and wolf behavior by videotaping their reactions, and, as expected, dogs did raise their eyebrows more often and more intensely than wolves. Even though wolves don’t have that muscle, they have a lot of other muscles so they can do a bit of the look.

Researchers dissected the heads of four wolves and six dogs, all of which they acquired after deaths in which they had no part. As might be expected from animals so closely related, all the musculature was exactly alike except for the levator muscle, which none of the wolves had. One other muscle, which varied in the wolves and dogs, was also related to eye movement.

The scientists hypothesize that humans have unconsciously favored eyebrow-raising dogs during fairly recent selective breeding. Dr. Burrows said that one tantalizing hint that could lead to future study was that one of the dogs, a Siberian husky, was more like the wolves and did not have the levator anguli oculi medialis.

Huskies are more closely related to wolves than some breeds, and it may also be that talent in sled-pulling was more important than a soulful face in the breed’s development.

Dr. Kaminski said, “the next step is to look at more breeds” to see if the behavior and the musculature varies. Perhaps dogs that are bred to work very closely with humans might be more likely to show the raised eyebrows which seem to indicate that the dog is paying attention.

And, she said, she would want to know whether the upbringing of a dog has an effect on this behavior.

As to what the meaning of the look is in the mind of the dog that gives it, and what dogs think of such studies of their facial expressions, science doesn’t have those answers yet.