Wolves and dogs can communicate using their eyes alone, suggests a new study in the journal PLoS ONE.
The color of the face around the eye, the eye's shape and the color and shape of both the iris and the pupil are all part of the elaborate eye-based communication system, according to the research, which could apply to humans as well.
Sayoko Ueda of the Tokyo Institute of Technology and Kyoto University led the study, which compared these characteristics of the face and eyes among 25 different types of canines.
The researchers identified three basic patterns:
A-type: Both pupil position in the eye outline and eye position in the face are clear.
B-type: Only the eye position is clear.
C-type: Both the pupil and eye position are unclear.
"A-type faces tended to be observed in species living in family groups all year-round, whereas B-type faces tended to be seen in solo/pair-living species," Ueda and colleagues wrote.
Wolves and dogs exemplify the A-type. Humans fit into this category too! Such individuals invite you to look into their eyes. The researchers even suspect that the white of the eye (sclera) evolved, in part, to set off the darker hues of the iris and pupil.
Animals like foxes exemplify the B-type. For them, some information is likely conveyed by the eyes to others, but not much.
Then there is the elusive C-type, exemplified by animals like bush dogs. Their all-dark eyes blend in with their furry faces. The researchers point out that "various predators camouflage their eyes to increase their hunting success." Consider that if you don't know what an individual is looking at, you can't predict his or her behavior.
Following the eyes can reveal interests and where an individual might go next. Both wolves and dogs are adept at following human gazes.
"The fact that the studied (canine) species with A-type faces tended to engage in group living suggests that they use the gaze signal in communication among group members, as the need for communication is larger for group-living species than for solo/pair-living species," the researcher wrote.
They added, "Group-hunting species had significantly lighter iris color (an important factor of gaze-signaling eyes) than those of solo hunting species. These results suggest that the gaze signal is used for communication during group hunting in many of these species."
Since we're social mammals too, perhaps we are revealing more about ourselves and our mental states with our eyes than we fully realize.
Photo: A wolf rests in the snow at Yellowstone National Park. Credit: Doug Smith, National Park Service