Few people can resist the “pidão” a dog makes when he wants affection, attention, or a snack. A new study has revealed key anatomical features that may explain what makes dogs so attractive. The findings also suggest that humans have contributed to dogs’ ability to seduce with facial expressions through thousands of years of selective breeding.
Dr Ann Burroughs said: “Dogs are unique among other mammals in their mutual bonding with humans, which can be demonstrated by mutual gaze, something we don’t see between humans and other domesticated mammals such as horses or cats.” and Professor in the Department of Physical Therapy at the John J. Rangos College of Health Sciences at Duquesne University in Pittsburgh, Pennsylvania. “Our preliminary findings provide a deeper understanding of the role that facial expressions play in interactions and communication between dogs and humans,” she explained.
Burroughs presented his research findings on Tuesday (5), the last day of the annual meeting of the American Anatomy Society, which has been held in Philadelphia since last Saturday (2).
The process of domesticating dogs selected facial muscles for faster responses
Dogs and wolves are closely related. While the exact timing is unclear, scientists estimate that the two species genetically diverged about 33,000 years ago, when humans began selectively breeding wolves, the first species to be domesticated.
The new study focuses on the anatomy of the small muscles used to form facial expressions, the muscles of mimicry. In humans, these tissues are dominated by myosin fibers that contract rapidly but also tire rapidly. This explains why we are able to form facial expressions so quickly, but without holding on to them for long. Muscle cells with slower fibers are more effective in long, controlled movements and do not tire as quickly.
For the study, the researchers compared myosin fibers in facial muscle samples from domesticated wolves and dogs. The results showed that dogs and wolves, like humans, have facial muscles that are dominated by fast-twitch fibers, but wolves have a higher proportion of slow-twitch fibers than dogs. “These differences suggest that having faster muscle fibers contributes to a dog’s ability to communicate effectively with people,” Burroughs said. “During the entire process of domestication, humans may have bred dogs selectively based on facial expressions similar to theirs, and over time dogs’ muscles could develop to become ‘faster,’ which benefits communication between them, dogs and humans.”
Under the new approach, having faster deciduous fibers allows for greater facial movement and faster muscle movement, allowing for small movements such as a raised brow and the short, strong muscle contractions involved in barking. On the other hand, slow spur fibers are important for prolonged muscle movements, and are also used by wolves when howling.
Looking at previous research, the team found that dogs have an additional mimic muscle that is absent in wolves and contributes to the expression of the ‘puppy’s eye’. The scientists say more research is needed to confirm their findings, with ways to distinguish additional types of myosin fibers, which could shed new light on the anatomical differences between dogs and wolves.
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