Lately, a paper to be published in the June edition of the American Naturalist has been getting some attention. The findings that are getting reported out of this paper didn't make sense to me, but I wondered if this was an issue with accuracy in reporting. So I went and found the paper. Turns out that the reporting is accurate, its the actual findings from the paper that confuse me. I really wanted to make sense of this paper, so I've been waiting a while to blog about it. But I can't make sense of one key finding.
But before we get to the confused, let's just review the paper, shall we?
The basic finding is that personality, energy expenditure, and longevity are correlated in domestic dogs. Dogs are a really good species to study the potential relationships between psychological attributes (like obedience), physical attributes (like body mass), physiological attributes (such as energy expenditure or metabolism), and average length of life.
Why are dogs ideal for addressing this question? Because there are over 400 different breeds which have been explicitly bred for various purposes. And It is unlikely that different breeders explicitly selected dogs on the basis of longevity or physiology; instead, most dogs were bred for specific jobs on the basis of morphology and trainability (i.e. personality). For example, Great Danes was bred as guard dogs, German shepherds as herders, and Pomeranians as companions. And different breeders in different locations bred different dogs for ostensibly similar purposes (tracking, herding, guarding, fighting, etc). And the different breeds are genetically distinct - there are more genetic differences between breeds than within breeds because breeders try really hard to keep their breeds genetically "pure" (i.e. purebred). (Keep in mind that even though the different breeds are relatively genetically distinct, all domesticated dog breeds still belong to the same species.)
The researchers picked out 56 breeds about which a lot is known about breed-specific personality, longevity, and energy expenditure. They labeled these traits "activity" which relates to general activity and excitability, "aggressiveness," relating to territorial defense and aggression towards other dogs, and "trainability," which refers to obedience, and they define as falling along a shy-bold dimension. They did a literature search and assigned scores for these three variables to as many of those 56 breeds as possible. They correlated these scores for each breed with adult body mass, mortality (risk of dying in the first 10 years of life), and "metabolizable energy intake," which means how much the dog eats.
They found three statistically significant correlations (say it with me: "correlation does not equal causation"):
(1) Activity correlated negatively with body mass. This means that bigger dogs are less active and excitable.
(2) Trainability correlated negatively with mortality. This means the more obedient breeds tend to outlive their more disobedient cousins. This is the one that's been getting all the attention in mainstream media.
(3) Aggressiveness correlated positively with energy intake. Breeds that eat more are more aggressive.
Longevity and metabolism are not explicitly selected for in breeding, nor are they included in breed standards. Additionally, different breeds were bred in different places by different groups of people. If you find a systematic relationship between two traits, one of which was explicitly selected for, like obedience, then it is reasonable to infer that the second trait varies as a correlated by-product of selection for the desired trait, instead of being simultaneously explicitly selected as well. So add longevity and metabolism to the list of things that are potentially correlated with personality, at least in dogs. This does, however, generate interesting hypotheses that are easily testable in humans, and that would be interesting.
Here's a big problem I have, and why this study confuses me. The authors say, in their abstract:
We found that obedient (or docile, shy) breeds live longer than disobedient (or bold) ones.
They say that obedience falls along a shy-bold dimension, with more obedient dogs being more shy. The experiments on the domestication of silver foxes in Russia showed that it was the more bold, less afraid foxes that were more willing to interact with humans. The more shy foxes were more afraid of humans and more aggressive. It doesn't follow that more shy breeds would be more trainable, because more trainable dogs need to be more willing to interact with humans. They need to prefer approach over avoidance. I expect that the more shy breeds would tend to be less obedient simply because they would prefer avoidance over approach. I'm not certain that these researchers are measuring what they intend to measure. So the finding that more obedient dogs live longer might suggest that more bold dogs - dogs who prefer approach over avoidance - are the ones that live longer. And if this is the case, there are some very interesting implications and potential physiological mechanisms that should be investigated, like the hypothalamic-pituitary-adrenal axis, which is involved in the stress response and approach/avoidance. To recap: it's not the finding (obedience related to longevity) that I have an issue with, its the measurement (shy dogs = more obedient) and the interpretation that arises from it.
I have one other big problem with this. Despite the fact that they conducted their literature search on 56 breeds, several of the correlations included far fewer breeds. Mortality rate data was only included from 19 breeds, and energy intake from only 9 breeds. So I'm less that impressed by these results. They did have body mass data for all 56 breeds. While the scatterplots look good and the regressions are highly significant, it only takes ONE datapoint to make or break significance in a correlation, even if you have a bajillion datapoints. If you DID have a bajillion datapoints, you could be reasonably certain that your correlation is legitimate, but with only 9 or 19 datapoints, it is uncertain.
So what are the take-home messages?
(1) These correlations are based on extremely small sample sizes, so interpret with caution.
(2) Domestication often has unintended consequences. As we continue to investigate the effects of domestication, we will likely find more things that are correlated by-products of selection for physical or psychological attributes.
(3) I'm confused. Or perhaps the paper authors are confused. I'm not sure. Does anyone have a different understanding than I do?
Careau, V., Réale, D., Humphries, M., & Thomas, D. (2010). The Pace of Life under Artificial Selection: Personality, Energy Expenditure, and Longevity Are Correlated in Domestic Dogs The American Naturalist, 175 (6), 753-758. DOI: 10.1086/652435
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Great danes were bred for hunting; specifically big prey like deer or swine.. Please just don't make stuff up, I generally consider your blog a nice reading; but I hate it when you seem to let your fantasy run loose like this.
If you want to get more confused, read the source paper (Svartberg 2002; http://tiny.cc/4ocp6) for the link between shy/ boldness and trainability; he has the relationship the other way around than what Careau et al have.
Svartberg 2002: "The results show that the shynessâboldness score is related to the level of performance: high-performing dogs have higher scores (i.e. are bolder) compared to low-performing dogs."
Careau et al "Given that trainability is inversely related to boldness in dogs (Svartberg 2002) [..]"
I'm with you; did they just switch the relationship round?
PS To RijkswaanVijanD: my dog book has Great Danes as being bred for both hunting and as guard dogs; don't be too quick to accuse people of making stuff up.
I'm sure the "activity"/body mass correlation is just the illusion of small animals being more "active". They're probably not actually moving faster than the big dogs, they just seem to be because they're smaller. (a dog that jumps four feet in the air looks more impressive if it's two feet high than if it's four feet high).
But wouldn't we expect an animal to be able to jump only a fixed multiple of their body height? No, that's an intuition that isn't borne out by biomechanics, which shows that an animal should be able to jump the same height in absolute centimeters, regardless of its own size. Similar considerations, appropriately scaled, apply to vigor in running, and so forth.
That's even if we discount the fact that metabolism doesn't scale one-to-one with size: so smaller animals have an actual greater metabolism per unit weight than bigger ones (doesn't a shrew look more energetic than an elephant? but the elephant is actually more active in absolute joules)
@3: I can't figure out in this paper how they measured "activity" but one would hope that it was more sophisticated than simply "moving fast" or "jumping a lot," etc.
They do note that artificial selection experiments on mice for high activity (measured by increased wheel-running) results in mice with smaller body mass at maturity, so I think there is probably something legitimate to this relationship - more than just measurement error.
Seems like more obedient dogs are gonna bond better with their masters, and be more likely to get more dollars spent on their medical care- more obedient breeds will be treated better. Or am I thinking too simplistically here?
I hope none of this dog research is being extrapolated to humans! So what if certain traits and physical attributes correlate in dogs who have been bred for various human-serving purposes? And so what if it's different in wild foxes (which are neither dogs nor humans?). IF (big if) I was interested in dogs, I would want to know whether the dogs studied were first matched on stage of life for the average of their breed and if all were treated somewhat the same from day to day. I would also like their activity to be measured using something objective like a pedometer (which we use for human studies of activity). Since rating scales have been used for "personality" and obedience, I'd like to see the development stages, validation and reliability information for those scales and finally, I hope the final raters were "blind" to the dog's name, owners, reputation and usual style of behaviour! By the way- were the researchers trained and experienced ethologists, used to observing animals?
Yah- who cares- they're just dogs!! Why did I bother commenting??
Liked this post! I agree - a very flawed study in so many ways.
One of the more annoying things about dog breeding is what individual breeds were bred for has changed recently and that may be enough dog generations to mess things up.
Some formally working breeds have been turned into guard breeds and many toy breeds used to be specialty hunter breeds(terriers good example). Dose any one still use German Shepherds for herding?
RijkswaanVijanD,
The UKC lists Great Danes as Guardian dogs even if at one time they were boar hunters.
The most obedient dogs are herders and gun dogs - both working groups that can't do their job unless they're super-fit and healthy. And they are often still selected for these traits today. Whereas most other breeds today are bred to conform to bizarre extreme show standards that probably shorten their lifespans, then kept as inactive, often obese pets. So I can see how the obedience/lifespan correlation might arise through both direct selection and lifestyle.
Also, how did they measure longevity? Ten is not very old for most breeds. I'd guess the vast majority of deaths in dogs under ten are due to being dumped, lost or killed by cars. Surely these fates are all more likely to befall disobedient dogs. So I hope they excluded these causes of mortality - if not the evo-devo spin is entirely unwarranted.
Adela [comment#8] is on the right track. When a dog-show announcer says that dog X was "bred to" work stock or hunt boar, what he really means is that a century or two ago, some of dog X's ancestors may have worked livestock or hunted. For at least a century, though, dogs in X's pedigree have not been selected for specific working abilities, but for size, shape, coat color, ear length, and so on.
Modern Shetland Sheepdogs have nothing in common with dogs that worked stock in the Shetland Islands 150 years ago. The modern German Shepherd is bred for show or for protection sports, not for stock work. Author Mark Derr has written that there are greater differences, personality-wise, between littermates than between dogs of different breeds. He has also written [in Dog's Best Friend, Henry Holt & Co., 1997] that "good breeding will often fade" before external factors like handling, socialization, nutrition and training.
[Rule of thumb among people who know the working border collie -- a purpose-bred dog breed -- is that it takes three generations of selecting for things other than the ability to work sheep and/or cattle for a dog to become useless at working stock. And please don't get me started on pet owners who say, "But Scout loves to herd the kids!"]
I see where your confusion is. One thought is that although the more bold foxes are more likely to approach humans, this likely has nothing to do with obedience. Maybe the shy foxes are more submissive (hence, don't have the guts to approach that big tall thing walking towards it), which means that they are more likely to place themselves in the beta role and allow humans to be the alpha. These bold foxes, though they're more friendly, may be less trainable specifically because they're not accepting a submissive role.