Since dogs began diverging from wolves tens of thousands of years ago, they’ve been changed for us, and by us, to suit us. This makes sense: natural selection describes how animals who have traits well suited to their environments are more likely to survive and bear young themselves.
Artificial selection, the process of domestication, by which humans have taken over the role of nature in determining who survives and can breed, is quite similar. Those animals who have traits well matched to us are more likely to be kept by us, and survive.
Thus, animals who we like – who we find useful, or cute, or cute and useful – will be successful. Another way of looking at this, though, is that those animals who have traits we like are good at using us to succeed. The dog is a case in point.
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How artificial selection changed how dogs look
Initially, there was almost certainly no intentional breeding by humans; rather, those proto-dogs or wolves who were the least fearful of us were most likely to be allowed near our homes and communities.
Over time, we began keeping dogs for functions they served: as guards or as hunting companions, for instance. Those who were kept were more likely to mate – or be mated – with other dogs serving that role.
The rise of pure breeding, breeding for looks more than for function, only arose over the last 200 years. But all along, we likely selected inadvertently for dogs who looked the way we liked and acted the way we liked.
This is where the ‘puppy-dog eyes’ come in. First, as a result of domestication, dogs typically have a neotenised, or juvenile, appearance.
They even behave in some ways more like young animals, playing together into adulthood (something much more rare among wild animals). Even when grown up, they retain a kind of infantile appearance.
Human babies have extra giant heads (relative to the typical adult head), big cheeks, chubby limbs and big saucer-like eyes. It’s thought that this prompts a human response to care for these helpless young humans. It turns out, in implicit preference tasks, humans prefer the look of dogs with large, baby-like eyes too.
But dogs do something special with those large eyes, something unlike what their nearest ancestors, wolves, do: they gaze at us and look into our faces. We humans look at each other’s faces in communication and empathy – and so do dogs. For wolves, by contrast, most eye contact is a threat. (Don’t try to share a loving gaze with a wolf if you come across one.)
So dogs are already looking at our eyes, and we at theirs, and this enables the feeling of mutual understanding.
But on top of that, researchers found that, unlike wolves, dogs have a special muscle, known as the levator anguli oculi medialis, or LAOM, muscle above their eyes. It allows them to raise their inner eyebrow in a beguiling way that reads as an appeal or as sadness.
An eyebrow-raising development
Humans make this eyebrow movement, too and we’re deeply attuned to it – perhaps even primed to respond to it. And it turns out that dogs living in a shelter who use their LAOM muscle when a person wanders by, are more likely to be adopted than the dogs that don’t.
A second eye muscle, the retractor anguli oculi lateralis (RAOL) muscle, pulls the outside corner of the eye back, enabling them to nearly smile with their eyes. The combination certainly prompts a nurturing response from us.
Are these large, human-gazing, eyebrow-raising puppy eyes just ‘manipulating’ us, as is sometimes said? Well, insofar as humans have almost certainly artificially selected dogs who have these familiar and beguiling expressions, it’s we who are the manipulators. Of domestic dogs’ physical features and of ourselves.
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