New Findings Challenge Previous Assumptions
Johannesburg, South Africa - A study published in The Anatomical Record challenges the long-standing belief that domestic dogs evolved their large, empathetic puppy-dog eyes to endear themselves to humans.
The research team has dismissed an earlier 2019 study that hypothesized that dogs evolved highly expressive faces due to their long history living alongside humans.
Expression of Emotion Not Limited to Domestic Dogs
The latest study, titled "Social Adaptations in the Facial and Ear Expression Musculature of the African Wild Dog," posits that large, soulful "puppy-dog eyes" did not evolve solely as a way for domesticated dogs to appeal to humans.
Instead, the study suggests that wild canid species are just as capable of producing the doleful eye expression as their domesticated counterparts.
Comparative Anatomy Uncovers Shared Adaptations
Previous research published in 2019 and 2022 theorized that dogs developed specialized muscles around the eyes to facilitate more effective communication with humans.
However, the new study refutes this theory, finding that wild canids have similar muscular adaptations, enabling them to make the same heart-wrenching expressions.
Wild Dog Anatomy Mirrors Domestic Counterparts
The earlier study compared the facial musculature of domestic dogs to that of wolves (Canis lupus) and found that dogs had developed specialized muscles around their eyes, allowing for a wider range of facial expressions.
The researchers concluded that these muscles likely evolved as dogs began living in closer proximity to humans, allowing them to mimic our facial expressions as a way to encourage us to care for them.
In the new study, the scientists dissected a deceased African wild dog (Lycaon pictus) specimen donated by a zoo and discovered that it possessed the same "puppy-dog eye" muscle development.
These facial muscles were not only present in the wild dog but were shown to be equivalently developed to those seen in their domesticated cousins.
Facial Muscles Aid in Ear Control
Additionally, certain facial muscles in the African wild dog appeared to support the intricate control of its signature large, floppy ears.
"This morphology suggests that facial displays involving the eyes contribute to intraspecific communication in wild dogs, not just in domestic dogs," the researchers wrote in the study.
Evolutionary Function in Wild Grasslands
"African wild dogs have just as much of that 'puppy-dog-eye' facial muscle as domestic dogs!" said Heather Smith, lead author of the study from Midwestern University in Illinois, USA.
The researchers believe that these eye muscles evolved to help African wild dogs coordinate and communicate as they hunt across open grasslands.
Sociality and Visual Signaling
Like wolves and their domesticated relatives, African wild dogs are highly social, living in groups of around 5-9 individuals.
Their highly expressive faces may allow them to create silent visual signals across the open landscape.
Future Research Directions
In the future, Smith and her team hope to examine the facial anatomy of other wild canid species, such as foxes, wolves, and Asiatic wild dogs, to see how well-developed their puppy-dog eye muscles are.
This will help them better understand how these species communicate and hunt, and help researchers determine whether this trait is present in species that are both social and visually oriented.
Expert Commentary
"This study confirms that not only [are wild dogs] highly social, but that a great deal of that social signaling is likely to be visual," said Adam Hartstone-Rose, a comparative morphologist at North Carolina State University not involved in the new research.
Hartstone-Rose notes that wolves, despite also living in close-knit social groups, may not have evolved facial musculature as robust as domestic dogs and African wild dogs because they rely less on visual communication.
Wolves hunt in varied landscapes, including dense forests and mountainous terrain, where individuals may be more likely to become visually obstructed by vegetation or terrain as they pursue prey. As a result, they may have evolved to coordinate using more complex vocalizations or scent marking rather than visual signals.
Summary
New research challenges the long-held belief that dogs evolved their large, expressive eyes to appeal to humans. The study reveals that wild canid species, like the African wild dog, also possess these facial muscles. This suggests that the ability to create "puppy-dog eyes" is an adaptation for communication and coordination, not just a product of domestication. Future research will explore the presence of these muscles in other wild canid species.