The evolution of "puppy dog" eyes

Here in the UK, we are certainly a nation of pet lovers! The UK charity PDSA reckons that over half of all adults have a pet. With marginally more of us having cats than dogs. But let’s start by talking about man’s best friend. Juliane Kaminski from the University of Portsmouth is interested in the evolution of human social interactions. And it turns out that studying man’s best friend - who shares quite a long evolutionary history with humans - can shed light on the human-dog relationship, and also, perhaps, how we came to be the way we are...

Juliane - Well dogs have obviously various ways to communicate with our owners. They can communicate through vocal communication, like barking and other sounds that they produce. They can communicate with their body postures and all kinds of things. But one form of communication that we became really interested in the recent years is what dogs do with their faces when they're looking at humans. So at their facial movements.

Katie - Is this where looking cute comes in?

Juliane - Yes, that's very much where looking cute comes in! Because we found that dogs produce a special eyebrow movement when they look at humans and that seems to be particularly appealing to humans. So humans have a really strong preference for dogs that produce that eyebrow movement.

Katie - It sounds like a very compelling theory, but you set out to investigate the science behind this. How do you go about studying this in a scientific way?

Juliane - Well, first of all, we were interested to see whether humans would really have a preference for dogs that produce that movement. And we did that by simply observing the behaviour of many different dogs in dog shelters. And we basically recorded all the kinds of behaviours that they produce when they meet a person. And then we asked the shelters to tell us how quickly those dogs were adopted. And we wanted to see if anything in the dog's behaviour made them to be adopted quicker than other dogs. And we found that it was particularly that facial movement that guaranteed a dog to be adopted faster than dogs that didn't produce that movement very often.

Katie - Can you describe this movement?

Juliane - It's what we call the puppy dog eyes. It's this moving the eyebrow up and a little bit inwards and it makes the dog face look really appealing to humans.

Katie - It's the kind of "help me, feed me, look after me".

Juliane - Yeah. It's a really interesting movement because it resembles a movement that humans produce when we are sad. So we have the theory that it might kind of trigger this natural response. So this kind of attention that we are directing at dogs comes from the same place that this kind of attention that we would direct at an infant, for example, that is producing this kind of movement. We are attending to this sad-looking creature.

Katie - Are dogs unique in this? Where did this particular movement or muscle that facilitates this movement come about?

Juliane - Yeah, we were really interested in that to see if there's any evidence that we humans might have unconsciously selected for this movement by simply preferring dogs that could use that movement and nurturing those dogs more. So we compared wolf faces and dog faces to see if there's any difference. And what we found is that the facial muscle structure of dog faces and wolf faces is almost identical. So the only difference is around the eyes. So exactly that muscle that produces this eyebrow movement is a muscle that we could find in dogs, but not in wolves. This is not something that happened consciously. So humans wouldn't have gone, "Oh, that's a really cute dog. Let me give that dog a little more food". So this is most likely something that happened unconsciously. So we simply had an unconscious preference for this movement, which kind of triggered this response of us wanting to attend to this creature. Therefore, we simply unconsciously selected this trait in dogs.

Katie - Kind of sounds like this says just as much about humans as it does about dogs.

Juliane - That's a really interesting aspect of this work. So it kind of raises a lot of hypotheses to some extent about our own species, so that these unconscious preferences can have such a strong or create such a strong selection pressure on another species. I think that's enormously interesting.

Katie - Do dogs use this muscle to communicate with anyone else? Other dogs, other species, or is it really particular to us?

Juliane - That's a very interesting question to which we do not have the answer yet, but that's one of the things that we are going to look at. And another very interesting question is whether dogs have in any way learned that this movement works with us. So is there any evidence that in some sense, they're producing this movement in an "intentional" way? So have they learned to manipulate us in any way? Or is it simply that they just produce that movement and it has no meaning for them? But it's simply humans selecting based on a trait that they find attractive, even though for the dogs themselves it means nothing.

Katie - Ultimately you're interested in how humans communicate with each other. So how does studying how dogs and humans communicate, how does that tell scientists like you about us? And how we communicate with one another?

Juliane - Well, I guess ultimately I'm interested in the evolution of these processes. So I'm interested in the evolution of human social interactions. And whenever we're interested in the evolution of something, we need to kind of find a model species that can help address some of these questions. And for many people, I guess, primates are the main model species when we are looking at human evolution. We might be interested in apes, as humans' closest living relatives. But dogs are fascinating model species because they have been domesticated and they've been living with us for such a long time. So the idea is that maybe this kind of evolution in a shared environment can kind of shed some light on some of the evolutionary processes in place.