Monday Pets: Biological Evidence That Dog is Man's Best Friend

The party isn't over yet! Here's another helping of Monday Pets. Enjoy!

Wild Dog crawled into the Cave and laid his head on the Woman's lap... And the Woman said, "His name is not Wild Dog any more, but the First Friend."

--Just So Stories, Rudyard Kipling.

ResearchBlogging.orgArchaeological evidence indicates that dogs were already a part of human society around the end of the Ice Age. Small dog skeletons have been unearthed in human communities as far back as 6- to 12-thousand years ago in Europe, the Middle East, and China. The jawbone of a domestic dog was found in a late Paleolithic grave in Germany, and dated to around 14 thousand years ago. And there is the famous site at Ein Mallaha (Eynan, in Hebrew), in Northern Israel where an elderly human and a 4-5 month old puppy were buried together, 10- to 12-thousand years ago.

i-0f84aed4b96c31971436fb52be48c091-ein mallaha.jpg

Figure 1: From the site at Ein Mallaha. The person's left hand is placed on the body of a 4-5 month old puppy.

Some evidence exists that dogs were the first animals to be domesticated, and until now, humans have only succeeded in domesticating around 20 different animal species. Compared with those other species (such as sheep, goats, pigs, cows, horses, donkeys, and camels), only dogs (and to some extent, cats, though at the risk of alienating readers, I maintain that cats are evil) have established for themselves a social niche within human society. Dogs were not only bred for companionship; some dogs were bred for hunting, guarding, or herding. More recently, dogs have worked as service dogs or drug-sniffing dogs. The question remains: Why do dogs have such apparent psychological effects on humans?

One hypothesis claims that humans develop positive feelings and behaviors towards dogs as a side-effect of a mechanism in place that forms the bond between parents and children. Attachment, or social bonding, is a sort of behavioral regulation system that exists to reduce the risk of harm (e.g. predation) to a young animal.

John Bowlby described two characteristics of the attachment relationship in mammals and birds:
(1) Parents maintain physical proximity to their young (and the young to their parents), and if that proximity is broken, they strive to restore it.
(2) Parents and their young display special behavior towards each other that they would not display towards others of their species. Parent-child relationships are specific, and characterized by individual recognition and differential behavior.

Most studies of dog-human attachment have relied on psychological scales and questionnaires. One group of researchers, however, from Azabu University in Japan, have attempted to provide a biological perspective to this question.

They begin with the assumption that individual recognition is essential for long-term bonds between between individuals. This is not as trivial as it sounds. Human adults are extraordinarily bad at distinguishing among monkey faces, for example, though highly skilled at distinguishing among human faces.


Figure 2: I promise, those monkey faces belong to different individuals.

Previous research showed that dogs are able to discriminate between human beings, and they're able to do it in a multimodal way, combining both visual and auditory stimuli. For example, they tend to look longer at a picture of their owner when it is paired with a recording of their owner's voice than with a stranger's voice. Other research has demonstrated that both human infants and dogs, but not human-reared wolves, behaved differently with strangers than with their owners (or parents). Is there a physiological mechanism that underlies this behavioral pattern?

Under normal resting conditions, the heart rate (HR) shows regular variation in beat-to-beat intervals. This variation is referred to as heart rate variability, or HRV. In dogs, HR increases during periods of increased physical activity (as would be expected), but HRV increased when dogs were playing with their favorite toy. So while HR is a measure of activity, HRV may indicate attention. The ratio of the low frequency part of the HRV pattern to the high frequency part is considered to reflect the activity of the autonomic nervous system.

Seven adult dogs and their owners participated in the study. The dog was put into an enclosure, and then presented with three strangers and their owner. Each of the strangers was of the same sex and of similar appearance to the owners. Each individual (the three strangers and the owner) were present for 4 minutes each, with 3 minute intervals between them. HR and HRV were measured during each stimulus presentation.

They found that HR and HRV decreased significantly between the first stranger and the third stranger, and this was probably due to habituation; the dog became used to seeing strangers. Then, when the owner was presented, HR and HRV both significantly increased.

Figure 3: HR when presented with strangers 1-3, and then the owner (top). HRV when presented with strangers 1-3, and then the owner (bottom).

As you can see, the difference in HR and HRV between strangers 1 and 3 is significant, as are the differences in HR and HRV between stranger 3 and the owner. This means that not only do dogs discriminate between their owners and other humans, but they also display an emotional response towards them (as indicated by the autonomic arousal). So at least one of the criteria for attachment, individual recognition, is fulfilled.

Pretty cool. But there's more.

When a social bond is broken, animals exhibit separation anxiety (I have scratch marks on my door to prove it) and a stress response in the endocrine system is activated. It is important to differentiate this form of attachment-based social bonding from a more general form of social affiliation. When separating monogamous animal pairs, separation anxiety and the endocrine response both occur. But separation of mates in a polygamous species does not elicit the physiological endocrine response.

Oxytocin is a hormone that occurs in the brain, and is important for bonding between mating pairs and between parents and children (Sci has covered oxytocin exhaustively, if you're interested). Increases in oxytocin levels are implicated in infants' memory formation of their caregiver, and in the process of pair-bond formation in monogamous species (like prairie voles). If you give prairie voles a drug that blocks oxytocin just before mating, the pair-bond won't form. Oxytocin given to stressed out animals (humans included) will cause them to relax, and cope with the stress. Oxytocin has even been called "the most important neurotransmitter that is responsible for social bonding." So you might expect oxytocin to figure prominently in the human-dog relationship.

Fifty-five human dog owners participated in this experiment, and all answered a brief questionnaire regarding their relationship with their dogs.
Experimental condition: First the owner pees into a cup. Then they play with their dogs for half an hour. Then they pee into a cup again.
Control condition: First the owner pees into a cup. Then they are made to sit facing a wall, and not interact with their dogs for half an hour. Then they pee into a cup again.

Then the experimental group was split in half on the basis of how long their dogs looked at them while playing. There was a strong correlation between gaze duration and the strength of the relationship, as assessed by the questionnaire.

And guess what? Those in the experimental group who had stronger relationships with their dogs also had more oxytocin in their urine, compared with the other group, who reported weaker relationships with their dogs! So the initial hypothesis, that the human-dog relationship emerges out of a mechanism initially designed to stimulate and maintain the parent-child relationship, may indeed be supported!

The changes in HRV as well as attenuation of oxytocin are both probably related to activity of the hypothalamic-pituitary-adrenal, or HPA, axis (which is involved, among other things, in the stress response).

There's still a lot left to figure out, but this study was a pretty important piece of the puzzle. It provides a clue as to the neural mechanisms that support the relationship between dogs and humans. It may also suggest a physiological mechanism to account for anecdotal reports of health-related benefits following animal interaction, but a lot more research is needed for that. It may also be the case that the attachment system in both humans and dogs share a similar neurophysiological mechanism (via the HPA axis). That may explain why dogs have adapted so easily to human society, and why humans so readily treat dogs as part of the family.

Nagasawa, M., Mogi, K., & Kikusui, T. (2009). Attachment between humans and dogs Japanese Psychological Research, 51 (3), 209-22.1 DOI: 10.1111/j.1468-5884.2009.00402.x


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OK, I'm convinced by a lot of lines of evidence (more than presented here) that dogs and humans have a very close relationship, we've influenced each other's evolution, we're kind of made for each other.

But how are there cat people? How are there people who naturally hate dogs? I've never liked or trusted dogs. Barking - to me - is one of the most hateful sounds I can hear. I like a cute dog (especially if it's quiet), but I'd hate to own one, and I can't stand to hear one. They sound like they're saying "Fuck you!" every time they open their yaps.

Cats may not give a shit about human beings, but they don't offend me that way. What gives? Why do a large fraction of humans hate dogs, if we're so close? It isn't ancestral memory of predation, because wolves are mostly silent. Hell, most predators are silent when they kill you. Hit me with some hypotheses.

By great.american.satan (not verified) on 12 Apr 2010 #permalink

I contend that cats were never domesticated, in the sense that dogs & livestock have been. Cats have merely occupied a novel trophic niche through their association with humans. The degree of artificial selection brought to bear on cats is miniscule compared to that of domesticated animals, and largely consists of manipulations of natural color variations that can be maintained due to relaxation of predation risk in association with humans.

A dog's barking is supposed to sound hateful, satan. If it sounded pleasant it would be ignored or at least wouldn't be considered a warning of danger. Same with a baby's crying - the baby wouldn't get the attention it needs if its squalling was pleasant to the adult ear.

By darwinsdog (not verified) on 12 Apr 2010 #permalink

Very interesting stuff, and congrats on movin' up in the sci-blogging world! :-)

I'm humored by your comment on cats - I find cats evil too, but only because I'm allergic to the little dander factories. Besides, dogs seem to have so much more personality, and I'm a sucker for emotional-attachment.

@GAS - There are plenty of humans who don't like children either, not just the sound of a baby crying, but even the sounds of kids laughing and playing. The hypotheses for why this is might also apply to why some individuals don't like dogs. Besides, the data discussed here doesn't say that all people will like all dogs, or vice verse, but that dogs and owners that are close have a biological connection similar to that between a child and parent.

I've heard a hypothesis that dogs were what gave us the advantage over the Neanderthals. By allowing dogs to do our sniffing, we were able to allocate more skull space to brains, to do things like outsmarting Neanderthals.

And I'm quite aware of the bonding that occurs between us and our canine companions. I have a Newfie-Lab hybrid underneath my office chair right now. Despite the risk of getting her tail run over, she wants to be as close as possible.

By GoatRider (not verified) on 12 Apr 2010 #permalink

...but that dogs and owners that are close have a biological connection similar to that between a child and parent.

Indeed. The argument is that dogs "hijack" a system that initially evolved for a somewhat different purpose. Not that humans are somehow "wired" to love dogs.

Dr. O is also correct in her observation that just as there is a continuum of how much people respond to certain cues from children, there is similarly a continuum in terms of how people respond to dogs. And that continuum can be characterized biologically.

Oh for Pete's sake. What is it about dog people that makes them all say cats are "evil"? How can a cat be "evil"?

I am an animal person. I have had a half dozen dogs, a half dozen cats, fish, a ferret.

Cats certainly do care about people. The reason they do not *seem* to care as much as dogs is we do not let our dogs run wild. We do cats. The fact that we let our cats roam, allows them to remain mostly independent and autonomous. Dogs are bound to us. Servile. Stray dogs and packs are swept up by by-law enforcement, where cats are not.

So, arguably, a cats affection and love is far more mature and genuine than a dog's dependency based relationship, because it is given freely. If a cat likes you, he/she actually likes you. A dog just grows dependent, like a weak willed human being. They need humans (or a pack). Cats do not.

We admire dogs because they are social animals like us. We admire cats because they are self reliant, like we want to be.

Anyway, the point of this is, in a scientific based blog, it is best to keep personal statements like "cats are evil" out of the articles as it tends to diminish credibility due to an appearance of eroded objectivity, and as can be clearly seen in the comments, detracts from the main point.

By Someguyouthere (not verified) on 12 Apr 2010 #permalink

"Dr. O is also correct in her observation that just as there is a continuum of how much people respond to certain cues from children, there is similarly a continuum in terms of how people respond to dogs. And that continuum can be characterized biologically." -Jason G. Goldman

And rabbits and doe eyed deer. This is a gross over simplification/generalization.

By Someguyouthere (not verified) on 12 Apr 2010 #permalink

And rabbits and doe eyed deer. This is a gross over simplification/generalization.

The difference is that dogs are very good at using human signals. They follow human eye gaze; they understand the pointing gesture. This is not a small thing. No other wild-type or domesticated animal (that has been tested) has been able to do these things. The Russian domesticated silver foxes come close, but domesticated dogs still win. Cats moderately succeed on the pointing gesture, but not with eye gaze.

Humans are also extraordinarily sensitive to things like mutual attention and joint eye gaze. The measure that correlated with the increase oxytocin and self-reported relationship quality was eye gaze.

I'm going to anthpomorphize to make this point: dogs seem to take advantage of their owners' sensitivity to eye gaze in order to facilitate the attachment bond.

It is not that "people love dogs." The attachment bond is *bidirectional*. People "love" dogs who exhibit behavioral cues that call the neural/hormonal attachment system into action, the same way that people love babies who exhibit behavioral cues that activate the attachment system.

The hypothesis that emerges from this is: If other animals (goats or bunnies or great white sharks or even robots) learn to perform these behavioral cues (eye gaze, in this example), then that should equally activate the attachment system. It's not the dog, per se, its the behavior that dogs as a species have gotten good at performing.

The other hypothesis (which is supported by this paper) is that individual dogs who are BAD at things like following eye gaze will NOT activate the attachment bond with their owners. This is an over-simplification, though, since nobody has proved a causal relationship, just a correlation.

There may indeed be individual cats (or horses or zebras or koalas) who DO succeed at things like following eye gaze. You would expect, in this case, that they'd indeed activate the attachment system.

Cats have that wonderfully addictive intermittent reinforcement system that seems to work for them. Mamzers.

I like cats but I'll be the first to point out that they are made for killing. They literally can't help it; they have knives for fingers and a bear-trap mouth for a hand. Watching a kitten play with an insect or lizard, just as it would with a flower bud or ball, and inadvertently kill it taught me more about cats than most of the reading I'd done on the subject.

@ #8 someguyouthere

So, arguably, a cat's affection and love is far more mature and genuine than a dog's dependency-based relationship, because it is given freely. If a cat likes you, he/she actually likes you. A dog just grows dependent, like a weak-willed human being. They need humans (or a pack). Cats do not.

I so totally agree with this. I'm a cat person (4 quirky, individual, perfect indoor-only felines at the moment), a dog person when I'm living in a situation that warrants having a dog (room to run, time for walks/exercise, etc.), and a horse person (riding instructor with a string of 27 school horses, with whom I work daily).

I like cats because they aren't obsequious and overly dependent. Sure, they welcome me at the door when I come home, follow me from room to room, alternate their lap-sitting duties, and sleep on the bed with me. But unlike horses and dogs, I can't get them to do this with the judicious use of a treat (I've never known such a non-treat-eating group of cats). I can't bribe a cat the way I can a dog or a horse. I like that!

There's nothing evil about that. Yes, they shed buckets -- so do dogs and horses. Yes, they run around the house at odd hours. Yes, they poop a lot (but I'd far rather clean 4 litter boxes than 4 stalls, or poop-scoop a yard full of dog doo). Yes, they scratch furniture if they don't have alternate scratching surfaces. (All 4 of my cats have claws all around, and I have designated one sacrificial piece of old upholstered furniture for scratching, and I have tons of cat scratchers around. No other furniture suffers. I've also replaced some of my antique hooked rugs with sisal carpets. I'm figure I'm better at adapting to their habits and requirements than vice versa!)

"Cats are evil"? Them's fightin' words, you know. And you don't want to make us crazy cat ladies angry. (You wouldn't like us when, etc.)

Yes, but is the failure of cats to do as well on the pointing and eye gaze tests really because they don't form "bidirectional attachment bond", or is it because those tests are not the *correct* tests to use for cats? Dogs are, as a group, much more social then cats (however domesticated cats are still more social then undomesticated or feral cats). The eye gaze and pointing tests seem more a test for sociality then for a bidirectional bond. IMO cats are just as good as picking up on human action, and interacting with humans, as dogs, they just do it differently.
For example: my cat wanted to interact with me earlier (wanted to lay on my lap and be petted) so he nosed me. Dogs would probably bark or get a favorite toy and drop it in front of their owner - both are much more active and social then what my cat did.

Welcome to Science Blogs! Just added you to my reader...I wanted to study this once upon a time, but science pulled me elsewhere, as it has a tendency to do.

So have you read anything about if the ability to use behavioral cues to the greatest effect varies by breed? My grad seminar just discussed a paper about how many breed-specific traits (well, the focus was on morphological traits, mostly) are a result of allelic variations in tandem repeats. Since they're relatively easily mutatable (reversibly so), they make good targets for breeding (not that the breeder would know that, of course). So I'm curious as to whether the variation in 'bonding behavior' is greater between individuals that between breeds.

"It is not that "people love dogs." The attachment bond is *bidirectional*. People "love" dogs who exhibit behavioral cues that call the neural/hormonal attachment system into action, the same way that people love babies who exhibit behavioral cues that activate the attachment system."

Actually, my cats do a lot of eye contact. The "sleepy eyes" thing they do is pretty sweet. Conversely, the cat who does the most staring has a really impassive face that amuses or creeps out my girlfriend by different turns. The cats seem to like me the most by a wide margin, which annoys her to no end. Guess I should've encouraged her to feed them occasionally years ago. Now I am the King of All Cats.

So yes, cats are evil. And that is why they rule.

By great.american.satan (not verified) on 12 Apr 2010 #permalink


I'm not sure that's data-based. I mean, my dog noses me for attention or puts her paw on my leg; my roommate's cat yowls loudly. I think the point is that cats' human interactions are fundamentally different from dogs', and perhaps not based on the same easy recognition of social cues that dogs employ.

...for instance, no cat I've ever met seems to realize that I don't like being randomly bitten for no reason.

It would seem that since dogs are hardwired to behave as a social group, the pack, it's transition to our innate human social structure doesn't seem like it's such a stretch. Cats on the other hand, do not form packs, and instead is hardwired to react socially only to its litter mates or mother and so it brings me dead birds, licks my head other stuff it might do to other cats from within its familial structure, and even then, with some restraint usually, and naturally.
The interesting thing with domestic animals is that they dont' seem to develop the instinctual reluctance we see in the adult ancestral animals from which they originated to see others as part of their social unit whether it's a pack, or a litter, or a tribe.

"...for instance, no cat I've ever met seems to realize that I don't like being randomly bitten for no reason"

No, they realize it.

This was another excellent article. Yes, cats are evil little creatures who shamelessly torture and kill anything helpless that catches their eye, but I love my kitty companions as much as my doggy companions and human companions. Many families have drama and cats play an important role in keeping the soap opera kind of drama flowing. Oh, and I think my little neko has succeeded at activating my attachment system as one of the most vocal, playful, and needy cats I've ever known.

By aratina cage (not verified) on 12 Apr 2010 #permalink

Don't want to be part of dog vs. cat war, I think it is the best combination of having one of each, they will stimulate the child - parent style bond (dogs) and cats will secure oxitocins flow on rainy, winter evenings when dog comes back from the walk to dirty to cuddle :)

Just read your first two entries and here's my suggestion: more stats!

I realize you're linking to research that has clearly stated statistical information, but the more you point out the actual measured effects from research in your article instead of using more qualitative statements, the less "MY DOG DOESN'T DO THAT!" responses you're going to get. A lot of developed animal behaviors exist because they add a few percentage points to the likelyhood of survival and reproduction to certain members of the species, but people tend to like statments like "dogs do x because of y" and unless you make it more explicit, that's what people are going to hear.

For instance, I was going to respond about cats and gazing because my cats do it all the time (indoor cats, that seems to make a difference), then I realized that probably lots of cats do it all the time, they just score lower as a group than dogs. Avoiding statements like "dogs do this, cats do this" is good because they're inadequate descriptors (like a comedian doing the "black people are all like 'this', white people are all like 'this'" routine). Anyways, I like the tone of the blog and I like the topic, I'll be coming back for more.

By mikerattlesnake (not verified) on 13 Apr 2010 #permalink

I think that the whole cat v dog thing is due to how long the human species has had domesticated dogs as opposed to cats, as well as how the "job" of cats was to operate independently.

While even people who do not like dogs are aware of basic dog behavior (i.e. wagging tail=happy), even people who have owned cats their entire lives can be greatly ignorant of the rules of cat behavior, interaction and body-language.

Example: the entire "my cat can randomly freak out and bite me when I pet it" thing. My cats never do that. I read umpteen cat-behavior books before I got my kittens; I learned that cats have very tiny body language signs that they think are loud and clear but that humans can miss entirely. If one of my cats presents me with a tummy to scratch, I am careful to watch for the tiniest sign that the cat has had enough of that rather than go past my cats comfort level and end up with claws and teeth wrapped around my wrist.

Beyond the extreme subtlety of cat body language, a lot of cat language is the opposite of Dog body language or is just flat out confusing. You should never approach a cat when it's tail is wagging; it is NOT a happy cat! Cats can purr when they are happy, but they also purr to self-comfort when they are injured or sick (and likely to lash out).

To me, Dogs are something that Humanity has been living with for so long that we instinctively understand their body language to a certain extent. We don't have that natural affinity with cats, but we can learn to understand them if we try.

My point was more that the formation of a bidirectional bond is based on many different behaviors, which also manifests differently in different species, and in different individuals. Just because one species typically does poorly at certain tests does not mean they don't form bonds with people.

Layman's Breakdown
Dogs = Unconditional Love
Cats = Unconditional Indifference

i love my cats and my dogs. but cats aren't 'independent'. they're just too stupid to interact with a human on anything but the most basic level.

cats have also definitely been domesticated to some extent. they had to be wild once, right? have you ever tried to cuddle a bobcat? it's surprisingly painful. or so i've heard.

By jackralph (not verified) on 14 Apr 2010 #permalink

Haha! Good stuff. I obviously favor cats, but I admit they are stupid as heck and have violently uncivilized instincts. BTW, I think the "random" biting of some cats isn't a matter of "going past the comfort level" as it is from some kind of freaky S&M thing. In my experience, cats who are enjoying petting too much will turn around and bite you because of that enjoyment. Not all cats though, just about 40% of the ones I've known. Not that I get bit (I see it coming), because I'm also a good read of cat behavior. My apartment has cat psychology all over it. I never leave something small by the edge of a surface unless I'm OK with it being knocked over, for one example.
Cats cats cats! OK, I am getting off-topic. Adios.

By Great American Satan (not verified) on 14 Apr 2010 #permalink

In the playing-with-your-dog experiment, the control condition should have been playing with someone else's dog, not staring at a blank wall. Otherwise, it could be that playing with any animal increases your oxytocin. Or that any kind of playing does. Or any kind of activity. Or that staring at a blank wall reduces oxytocin from basal levels...

In the playing-with-your-dog experiment, the control condition should have been playing with someone else's dog, not staring at a blank wall.

I agree, this makes sense. Maybe they're doing that study now. That might be the logical next step.

We got our first family dog in July, because the kids are old enough and naturally wanted a real pet. Unfortunately, the cat we had for several years is pretty anti-social. But she solved the rodent problem. I sort of liked dogs. But damn if I'm not smitten with this dog! I wondered why I almost feel bonded to a mammal I never breast-fed.
The article mentioned a combination of visual and auditory recognition, but what about smell? I thought dogs relied as heavily on that as humans do on sight. Maybe it would be more difficult to humans to evaluate.
My sweet Golden Retriever/Border Collie shelter mutt has since turned me into a dog-lover!

By laursaurus (not verified) on 17 Apr 2010 #permalink

I love my dog and she seems to worship me but I am also convinced that she is really a furry cuckoo engaging in an extremely sophisticated brood parasitism.

Stray dogs and packs are swept up by by-law enforcement

Not where I live. Here in OKC, I haven't seen a patrolling animal control vehicle in nearly a decade. Budget shortfalls and what-not. Not that I know it to be truth, but a coworker of mine that does a lot of work with her local animal shelter has told me that they will take your contact information and bill you, should you request an animal be picked up. And we have lots of strays. On the east-side of the city, you can barely go a block w/out seeing at least one stray pit bull.

That being said, I am a dog and cat person, though I like dogs much better, owning 1 dog (lab/newfie mix) and 0 cats. I grew up with cats and find them affectionate enough, but they lack any usefulness, outside of the stress release of petting them. Dogs, because of their "obsequiousness", can almost seem an extension of the human mind and body with minimal training.

Also, cats poop inside the home as a matter of course. They walk in their own excrement, then go plodding over counter-tops, couches and bed-sheets. While they are certainly less than evil, this fact alone makes for an irreconcilable difference between cat ownership and an objectively hygienic living space.

By cgauthier (not verified) on 27 Jul 2010 #permalink