As Dog Dads, we love finding out science about
our canine kids. Here's a fascinating scientific study that came out in
June.
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| Tyler has very expressive eyes |
In the news: Dogs' Eyes Have Changed Since
Humans Befriended Them
Atlantic June 20, 2019
Dogs, more so than almost any other domesticated
species, are desperate for human eye contact. When raised around people, they
begin fighting for our attention when they’re as young as four weeks old. It’s
hard for most people to resist a petulant flash of puppy-dog eyes—and according
to a new study, that pull on the heartstrings might be exactly why dogs can
give us those looks at all.
A paper published on June 18, 2019 in the
Proceedings of the National Academy of Sciences found that dogs’ faces are
structured for complex expression in a way that wolves’ aren’t, thanks to a
special pair of muscles framing their eyes. These muscles are responsible for
that “adopt me” look that dogs can pull by raising their inner eyebrows. It’s
the first biological evidence scientists have found that domesticated dogs
might have evolved a specialized ability used expressly to communicate better
with humans.
For the study, a team at the University of
Portsmouth’s Dog Cognition Centre looked at two muscles that work together to
widen and open a dog’s eyes, causing them to appear bigger, droopier, and
objectively cuter. The retractor anguli oculi lateralis muscle and the levator
anguli oculi medialis muscle (mercifully known as RAOL and LAOM) form two
short, straight lines, which connect the ring of muscle around a dog’s eye to
either end of the brow above.
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| Franklin |
These researchers have long been interested in
the ways dogs make eye contact with humans and, in particular, how they move
their eyebrows. In 2017, Juliane Kaminski, the lead author of the new paper,
found that dogs moved their eyebrows more often while a human paid attention to
them, and less often when they were ignored or given food (which, sorry to say,
is a more exciting stimulus for them than human love). That suggested the
movement is to some degree voluntary. On our side of these longing glances,
research has also shown that when dogs work these muscles, humans respond more
positively. And both man and mutt benefit from a jolt of oxytocin when locked
in on each other.
This isn’t simply a fortuitous love story, in
which the eyes of two species just so happen to meet across a crowded planet.
Like all the best partnerships, this one is more likely the result of years of
evolution and growth. If dogs developed their skill for eyebrow manipulation
because of their connection to humans, one way to tell would be to look for the
same capacity in wolves. Because dogs split off from their wolf
relatives—specifically, gray wolves—as many as 33,000 years ago, studying the
two animals is a bit like cracking open a four-legged time capsule. Divergence
between the two species marked the start of dogs’ domestication, a long
evolutionary process influenced—and often directly driven—by humans. Today,
researchers can identify and study differences between the species to gain an
understanding of exactly how dogs have changed over time.
In this case, those eyebrow-raising muscles do
appear to be an addition to dogs’ anatomy. In the four gray wolves the
researchers looked at, neither muscle was present. (They did find bundles of
fibers that could be the precursors to the RAOL and LAOM.) In five of the six
breeds of dogs the researchers looked at, both muscles were fully formed and
strong; in the Siberian husky, the wolflike, oldest breed of the group, the
researchers were unable to locate a RAOL.
Sometimes, the origins of changes like these
aren’t immediately apparent. Certain physical dog traits—including floppy ears
and short snouts—likely originate from the same set of developmental cells that
code for tameness, a preferable trait in household pets, for instance. In the
case of this new research, though, the connection between the physical trait
and the related behavior is a bit more direct. “Previous work—and much of it by
these same authors—had shown that these muscles were responsible for enhancing
positive responses in humans,” Brian Hare, the director of Duke University’s
Canine Cognition Center and the editor of the paper, told The Atlantic via
email, “but the current suggests the origin of these facial expressions is
after dogs split from wolves.”
By evolutionary standards, the time since this
split has been remarkably short for two new facial muscles to have developed.
For a species to change that quickly, a pretty powerful force must be acting on
it. And that’s where humans come in. We connect profoundly with animals capable
of exaggerating the size and width of their eyes, which makes them look like
our own human babies and “hijacks” our nurturing instincts. Research has
already demonstrated that humans prefer pets with more infantlike facial
features, and two years ago, the authors of this latest study showed that dogs
who made the facial movement enabled by the RAOL and LAOM muscles—an expression
we read as distinctly humanlike—were more likely to be selected for adoption
from a shelter than those who didn’t. We might not have bred dogs for this
trait knowingly, but they gained so much from having it that it became a
widespread facial feature. “These muscles evolved during domestication, but
almost certainly due to an advantage they gave dogs during interactions with
humans that we humans have been all but unaware of,” Hare explained.
“It’s such a classically human system that we
have, the ways we interact with our own infants,” says Angie Johnston, an
assistant professor at Boston College who studies canine cognition and was not
involved with the study. “A big theme that’s come out again and again in canine
cognition and looking at the domestication of dogs is that it seems like they
really just kind of dove right into our society in the role of being an infant
or a small child in a lot of ways. They’re co-opting existing systems we have.”
The same humanlike facial gestures could also
be a dog’s way of simply securing attention in the first place. Eyebrow raising
is one of the most well-understood examples of what researchers call ostensive
cues, a family of nonverbal signals (often facial movements and expressions)
humans send one another to convey their intention to directly communicate.
Dogs’ uncanny ability to mimic this human expression likely leads us to project
certain human emotions onto them in ways we don’t with other animals,
regardless of what they might actually be feeling.
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| Dolly |
The movement of the RAOL and LAOM muscles is
particularly open to interpretation. “In different contexts we’ll call that
something different,” says Alexandra Horowitz, a senior research fellow at the
Barnard College Dog Cognition Lab. “In one case, I might say it’s sad, but in
another case I’ll say, He’s really paying attention. It can look wry, like a
questioning or unbelieving look.” According to Horowitz, dogs are the only
animals aside from our primate cousins that are expressive in this eerily
familiar way. Horses alone share the ability to twist their eyes into the same
doleful shape, but their overall expressions don’t strike us as humanlike in
the same way that dogs’ do. With dogs, Horowitz points out, we’re so driven to
connect that we often search for “smiles” in the shapes of dogs’ mouths. The
new research, she says, “makes me think it’s more about being able to move the
face in a way that humans move the face. We don’t like unexpressive faces.”
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| Dash |
Both Horowitz and Johnston suggested that
similar studies looking at populations of dingoes (which Johnston researches)
and Siberian foxes could provide yet another time capsule of sorts for
understanding eyebrow movements and other evolutionary traits. Both species
live near humans and are some of the closest living relatives to the earliest
dogs. Why did they stay wild while dogs drifted into domestication? “Anything
to do with getting to the bottom of why we as a species picked out this one
animal can carry a huge amount of information,” Horowitz says. “In some ways,
it’s discovering something about ourselves.”
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