Why do big dogs have a shorter lifespan than small ones.Does the same apply to people

Why does, say, a Jack Russell have nearly double the average lifespan of an Irish Wolfhound.
It’s not like the Wolfhound has to struggle along with a terrier sized heart, etc.All it’s “bits” are in proportion to it’s size.
Why should a larger body size have such an effect on lifespan.
Does the same thing apply with humans.Do Pygmies live longer than Masai?
Apologies if this has been asked before but the search page will not accept the word dog as its less than 4 letters.

I’m not sure about why little dogs live longer, but I do have something to add.

I swear that Cecil did an article(not online though) about why we see no elderly tall people. He concluded that past a certain height, people live shorter lives. So it is true that tall people die younger.

Typically, larger bodies result in longer lifespans (For most mammals, the lifespan is proportional to the animal’s mass, raised to the 1/4 power). That the reverse effect appears in dog breeds would appear to have more to do with the particular breed than merely its size. And all bets are completely off when it comes to humans.

its to do with the amount of force needed to accelerate a body
related to its mass.
since dogs are friendly the big one needs to keep up with the little one and uses a lot of energy matching not only the speed but the accelleration
being bigger it thinks it should always win so overdoes the effort
my bitches were 15 when they died, both jack russells.

My WAG: The smaller dogs have been more in-bred than larger dogs, so are genetically less sound.

Can anybody with more dog knowledge than I support or refute my guess that the smaller dogs are generally in-bred more? My guess is takes more inbreeding to reduce size, but that is indeed just a guess.

Hmm, I wouldn’t think so, simply because if left to breed “naturally,” any given group of dogs (regardless of breed) in a feral population will, in several generations, come up with a generic, pariah type–as is evidenced by the Carolina Dog. They tend to range around thirtyish pounds, and I would guess selecting for smaller than thirty or forty pounds is less of a biological stretch than selecting for a hundred and fifty pound dog.
Plus, if smaller dogs were genetically less sound, wouldn’t they have the shorter life span?

Not an explanation, but another bit of information that may be connected. Smaller dogs typically have a much shorter adolescence and growth period than large or giant breeds. Most toy and small terrier breeds are considered to have reached full growth and maturity around a year, while large and giant breeds are just entering the throes of adolescence at eighteen months, generally lasting until two to two and a half years. You’d think that would mean they would live longer, no?


Square-cubed law? The more you scale up a given structure, the more stressed it becomes - the strength of bones and connective tissue scales to the square of the size, but the loads imposed square to the size cubed. So the same basic biology will be under more stress the larger you scale it. It’s why we can’t have ants the size of horses.

It’s why we can’t have any insect larger than a certain size-they wouldn’t be able to support their exoskeleton (learned that from watching Bill Nye the Science Guy). Though I did see something somewhere about 4 foot prehistoric spiders. That brings up a similar question-why have species become generally smaller? There are no 3-toes sloths or Icthisaurasus, the dinosaurs tended to be large too, and have all died. What assests do small animals have over larger ones I guess is the question. Maybe its the general fact that they can escape/hide easier?

That makes sense, I know you have to be very careful to control and slow the growth rate of large and giant breeds, otherwise their heart and skeletal system will be stressed and you will run into a lot of bone and joint, and general health issues later.


A vet I know once said that one of the main reasons that really large dogs have shorter lifespans is because of the amount of energy they use up in order to catch enough food for their size.

(That was worded horribly, so I hope you know what I mean.)

The conversation came about specifically because we were talking about an Irish Wolfhound who was rescued and brought to her clinic.

She said a bigger body requires “bigger” nourishment, but as carnivores big dogs don’t usually get it (they don’t graze all day like a cow) and Irish Wolfhounds don’t have huge stores of fat on which to draw. In the wild, they would use up a lot of energy to catch something and share it with the rest of the pack.

Large cats that sleep as much as possible to conserve energy to use in a big spurt to catch food. Dogs are so social they roam and DO lots of stuff in between meals, using up that precious energy and needing more food to replace it.

**NOTE:**That was her theory, but I don’t know if she was being really accurate or just speculating at the time.

Big animals that do nothing but graze all day have fairly long lifespans, as do smaller carnivores that can fill their bellies with lots of little snacks.

The above assumes a non-allometric scaling. Which, of course, is not how nature works. Elephant and large dinosaur bones are not just larger versions of the same bones found in smaller animals, they are typically much thicker proportionately to account for the extra load they must bear.

Which is completely different form physiological scaling. Lifespan is related to metabolic rate, and metabolic rates scale to the 1/4 power with respect to body mass in most animals. Again, the trend is for larger animals to have longer lifespans. If larger dog breeds have shorter lifepsans, it is almost undoubtedly a circumstance of their breeding, not of any scaling laws.

That the larger animals are extinct has little to do with their size in any strict sense (although, the survivors of the extinction at the end of the Creataceous were all small). There is, ultimately, no evolutionary “favoritism” towards either small or large animals. A significant factor in the absence of really large terrestrial animals today is us: we killed off a good many of our large contemporaries.

Yeah, I got mixed up there. I used to think the smaller dogs had the shorter lifespan, I guess because of my incorrect inbreeding theory. Thanks for the clarification!

After I read your post, I did a bit of Googling on the Carolina Dog. Interesting stuff! When you say ‘pariah type’, you mean a dog is produced that is rejected by the pack, and starts its own pack? The pariah type was mentioned in some pages I saw, but not explained.

Ah, but there’s the thing. We’re not comparing an elephant to a mouse. We’re talking about taking a wolf that’s spent millions of years adapted to a specific size, and in the space of a few thousand years breeding it to grow to an significantly smaller or larger adult size. The elephant has had millions of years to adapt to its size. The wolf bred into a mastiff or saint bernard hasn’t, and is under more physiological stress than a well-adapted animal of that size would be.

Except it isn’t by the breed. Small dogs consistently have long lifespans, except when heavily inbred or otherwise genetically unhealthy. Giant dog breeds consistently have shorter lifespans. It is true that some breeds live longer than others for the same size, but it is also the case that the larger dog breeds on average live shorter lives than the smaller ones.

Probably less than that. I believe active breeding of dogs has only been going on for 600 years or so.

Given that large breeds tend to succumb more frequently to cancers and heart disease than broken bones, I’d still say that the physical scaling isn’t a significant factor. And the size difference between the largest dog and the largest wolf is probably not sufficient for scaling effects to matter, anyway.

I didn’t say it was necessarily by breed, I said it was a circumstance of their breeding. The average life expectancy of a domestic dog is 8-9.5 years (in the U.S., anyway). Large dogs, by and large, may have lower life expectancies than smaller ones, but that has more to do with how they were bred than their absolute size (or rather, the effects of their breeding / inbreeding; I would suspect that the pool of available purebreds is greater for smaller dogs than for larger ones simply based on popularity). Once again: it is not because they are big that they live shorter lives. The smallest dogs are just as likely to experience problems as the largest. And hybrids can live to be much older than purebreds.

A pariah dog is sort of a general name for a usually feral, “primative” type of canine–kind of like what you’ll end up with if X number of random dogs were left to their own devices for a number of generations. According to encycolpedia.org, “PARIAH DOG, a dog of a domesticated breed that has reverted, in a greater or less degree, to a half-wild condition.” They seem to eventually revert to a dingo-esque, smallish, brushy coated, prick-eared generic type dog.
A number of breeds are known as primative, or pariah types, including the Caanan Dog, Carolina Dog, Basenji, and the New Guinea Singing Dog. Many of them revert not only in appearance, but other “survival” characteristics as well, such as bitches only having one heat cycle per year. This is evident in the Basenji, New Guinea Singing Dog, and possibly the Caanan dog–although I’m not certain about the Carolina Dog.


Are they called pariahs because they’ve been living and breeding on the fringes as they reverte, or because that’s the sort of dog that a pariah is likely to own?

Thanks again Mixie. Sounds like the term “pariah” in this context isn’t as analagous to other uses of “pariah” as I thought. Although I guess maybe it came from being outcast from human society, and not their own pack.

FYI, this site: http://www.carolinadogs.org/ says Carolina Dogs are decended from “the feral pariah canids who came across the Bering land mass 8,000 to 11,000 years ago as hunting companions to the ancestors of the Native Americans.”

I thought we didn’t see any elderly tall people because they all hunched over?

Sorry if that sounds mean, just what popped into my head.

Wrong answer.

look up dogs like pugs and pomerainians (sp?)

some dogs have been around for a long time.

of course google kicks back a ton of broken links but iirc pugs are close to 1000yrs old, pom’s were palace guard dogs (ala burgler alarms) for the chinese.