Unlike a certain companion animal that will go unnamed, dogs lose their minds when reunited with their owners. But it's not immediately obvious why our canine companions should grant us such an over-the-top greeting -- especially considering the power imbalance that exists between the two species. We spoke to the experts to find out why.
Call of the Wild
In order to gain an appreciation for dog behaviour, it's important to understand that dogs are descended from wolves (or at least a common wolf-like ancestor). Clearly, the two species, separated by about 10,000 to 15,000 years, share a lot in common.
Like dogs, wolves greet each other with vigorous face licking (Credit: Sander van der Wel CC A-SA 2.0)
But there's only so much we can extrapolate from wolves; dogs are categorically different by virtue of the fact that their ancestors actively sought out the company of humans. Making matters even more complicated is the realisation that Paleolithic era wolves are not the same as the ones around today. Consequently, any inferences we make about dog behaviour and how it relates to wolves is pure speculation.
"The most social of those ancestral dogs who were hanging around humans had to have been the most social of those wolves," he told io9. "They joined humans and eventually evolved to become dogs. The remainder of the wolf population were among the most antisocial of those animals, and did not want to have anything to do with humans."
That said, however, Berns says we can clearly see behaviours in wolves that are similar to those expressed by dogs. For instance, wolves greet each other by licking each others' faces. For these pack animals, this licking behaviour serves as an important social greeting, but also as a way to check out and determine what the other wolves have brought home in terms of food.
Wolves, says University of Trento neuroscientist Giorgio Vallortigara, greet each other in different ways depending on the type of individual relationships they have forged. Feral dogs, he says, behave in similar ways. But the big change in terms of adaptive sociality has been the ability of domesticated dogs to interact with humans using our own communicative signals, such as gazes and gestures.
"When I'm at Wolf Park in Battle Ground, Indiana, I am always struck by how much some of the specific wolf behaviours resemble behaviours I see in dogs -- but so much more ritualized, and sort of writ large," she told io9. "I witnessed one behavioural study there in which wolves who knew each other well had been separated for a few days and were put back together. The greeting rituals were fascinating, with lots of crouching and chin-licking from the subordinate wolves. You do see these behaviours in dogs, but more sporadically, without such intensity."
At the same time, dogs exhibit behaviours that are markedly different from wolves. As Hekman explained to me, one of the most dramatic differences between dogs and wolves is the ability of dogs to accept novelty. Simply put, dogs are less fearful than wolves.
"It may sound a little odd to say that a wolf, who can easily kill you, is afraid of you, but that is precisely why they can be dangerous: because they may choose to take proactive measures to protect themselves, using their teeth," says Hekman. "Dogs are a lot less likely to do this."
Indeed, given their wolf ancestry, it's remarkable that dogs get along with humans so well. But as Berns pointed out to me, sociability has turned out to be a rather powerful adaptation, one that has worked a lot better for dogs than it has wolves.
"I mean, look around the world and see how many dogs there are," he says. "With dogs, it's proven to be a highly effective evolutionary strategy. There are on the order of tens of millions of dogs in the world, so in many ways, dogs have out-evolved wolves."
Berns says that whatever the sociality that dogs have evolved, one of the defining traits of a dog is the degree to which they will interact with humans as well as other animals.
How Dogs See Humans
A key aspect of Berns' brain imaging research is to study how dogs perceive us. We humans know that dogs are a separate species, but are dogs cognisant of this as well? Or do they see us as members of their pack, or as some kind of weird dog?
Callie gets outfitted with ear protection prior to entering the noisy fMRI machine. The research team includes, from left, Andrew Brooks, Gregory Berns and Mark Spivak. (Credit: Bryan Meltz, Emory University)
According to Berns' research, dogs that are presented with certain smells in scanners can clearly tell the difference between dogs and humans, and also discern and recognise familiar and strange odours. In particular, the scent of a familiar human evokes a reward response in the brain.
"No other scent did that, not even that of a familiar dog," Berns told io9. "It's not the case that they see us as 'part of their pack as dogs,' they know that we're something different -- there's a special place in the brain just for us."
Berns stresses that dogs are social with us not just because of their scavenging tendencies.
"What we're finding with the imaging work is that dogs love their humans -- and not just for food," he says. "They love the company of humans simply for its own sake."
Hekman says it's hard to know what dogs are thinking, but she suspects they understand that we're not quite like them. As evidence, she points to aggressiveness in dogs as it's directed to other dogs and humans -- differences that aren't correlated. She says it's quite common for a dog to have a problem with one and not the other. In other words, dogs appear to perceive other dogs as one group, and humans as a separate group. What's more, dogs will seek the help of humans and not other dogs -- a possible sign that dogs understand that humans have resources that dogs do not, and are thus a different kind of social entity.
But do dogs see us as part of the pack?
"It's important to note that a pack of wolves is a family -- literally, usually mum, dad, puppies, and some young offspring from previous years who haven't gone off on their own yet," says Hekman. "Do dogs see us as part of their family? I think they do."
So Happy to See Us
Virtually all experts agree that the happiness dogs feel is comparable to what humans experience, and that it's similar to how humans feel towards each other.
One happy dog (Credit: Lars Curfs/CC-A-SA 3.0)
"All the things that we've done with the brain imaging -- where we present certain things to the dogs and map their reward responses -- we see analogous brain responses in humans," says Berns. "Seeing a person that's a friend or someone you like, these feelings are exactly analogous to what a dog experiences."
Berns says that dogs don't have the same language capacities as humans, and that they're not capable of representing things in their memory like we can. Because dogs don't have labels or names for people, he suspects that they have an even purer emotional response; their minds aren't filled with all sorts of abstract concepts.
It's also important to consider the dog-human bond and the degree of attachment each feels toward each other. When used with dogs, the "Strange Situation Test" devised by developmental psychologist Mary Ainsworth, suggests that during absence and then at the rejoining with the owners, a dog's behaviour is very similar to that observed in children and mothers in similar situations. As Vallortigara pointed out to me, it's appropriate and correct to speak of the dyad dog/owner in terms of "attachment."
A dog's particular greeting, however, is dependent on several factors, such as the dog's temperament, the personality of the owner, the nature of their relationship, the level of stress and anxiety, and the dog's tendency/capacity for self-control.
It's important to note, however, that stress manifests differently in dogs than it does in humans.
"The separation from the owner for the dog is not voluntary," says Vallortigara. "It is always unnatural for a dog to detach and abandon the pack."
Dogs will sometimes go solo on a temporary basis if they're sufficiently motivated to do so, but they do it knowing that social contact can be resumed at virtually any time.
"The exaggerated level of greeting that can be observed in some dogs is likely due to the fact that they have not yet learned to accept the possibility of non-voluntary detachment," says Vallortigara.
When trying to appreciate a dog's over-the-top greeting, Hekman says we need to imagine what it was like for a dog to be alone all day while we were gone.
So bored. (Credit: Pixabay/Pinger/10 images/CC0 Public Domain)
"This dog probably had a pretty boring day without much enrichment, and moreover may have been alone all day, which is unpleasant for a social animal," she told io9. "So in addition to being glad to see us, they are probably feeling some relief that they will get to do something interesting, like go for a walk, and have someone else around. Some people are able to have a dog walker come in or send their dogs to daycare -- this is a great solution to what can otherwise be a difficult lifestyle for a dog."
And as Berns points out, the greeting ritual is a social bonding mechanism -- but it's also a function of curiosity.
"When they jump up, they're trying to lick you in the face," says Berns. "Part of that is a social greeting, but they're also trying to taste and smell you to figure out where you've been and what you've done during the day. So some of it is curiosity. If I've been with other dogs, for instance, my dogs know it, and they resort to sniffing intensely."
How to Greet Your Dog Back
It's obviously important to respond to your dog when you get home, but according to Marcello Siniscalchi, a veterinary physician from the University of Bari, how you should react will depend on the context of the situation and the needs of the dog itself.
"The greeting ritual will vary from dog to dog because any individual dog perceives and reacts to detachment from the owner in a very personal way," he told io9. "Some dogs need to be greeted, in others it is better to avoid any escalation in the level of excitation, others need to learn strategies for coping the stress associated with detachment."
Hekman says there's definitely a tension between our buttoned-down greeting rituals ("Hi, honey, I'm home!") and theirs ("I want to lick you on the face repeatedly!").
"My dog Jenny is a very enthusiastic greeter, and I hate having her jump all over me in her efforts to get at my face," she says. "So I have taught her to get on a couch when I come home. I generally have to remind her to 'get on your couch,' but now she does with great enthusiasm, and waits for me to come over. The couch puts her more on my level, so she doesn't have to jump, and I can bend forward and let her lick my cheek, which is a very important part of the ritual for her."
Hekman stresses that, for any dog, it's important for us not to tell them what not to do (e.g. "don't jump on me!"), but to tell them what to do.
"Many is the retriever owner who has taught their dog to get a toy when they come home to channel their excitement," she added.
The main point, she says, is that it's important for dogs to have the greeting ritual, but it can be redirected in ways to make it easier on the owners such that everyone enjoys it.