PORTSMOUTH, ENGLAND—An international team of researchers led by comparative psychologist Juliane Kaminski of the University of Portsmouth examined the anatomy and behavior of small groups of dogs and wolves, and determined that dogs’ facial anatomy evolved to enable better communication with humans, according to a BBC News report. The anatomical study revealed that dogs have a small muscle, which is either not present or is underdeveloped in wolves, that raises the inner eyebrow. In the behavioral portion of the investigation, wolves and dogs were exposed to an unfamiliar human for a period of two minutes, and the researchers recorded the animals’ eyebrow movements. The dogs raised their inner eyebrows more often, and at higher intensities, Kaminski said, resulting in the “puppy dog eyes” expression. The dogs also moved their eyebrows more often when humans were looking at them. She and her colleagues suggest that the raising of the inner eyebrow mimics facial expressions made by human infants, and thus triggers a nurturing response in humans. Humans may have had an unconscious preference for dogs with expressive faces, leading to an evolutionary advantage, Kaminski explained. To read about recent genetic studies of dogs, go to “The American Canine Family Tree.”