How big can a dog get?

May 26, 2009 9:57 AM

How big and how small could a dog theoretically be? If people decided to breed the biggest dog possible, could they make one as big as a bear? If they tried to breed the smallest one possible, could they get it to the size of a shrew? If so, how many generations or how many years would it take to breed a bear-sized dog? I'm talking about standard breeding techniques, not genetic engineering.
posted by empath to science & nature (24 comments total)

Big mastiff-type breeds are already about as big as a somewhat-below-average black bear. So the answer is: it would take zero generations.
posted by ROU_Xenophobe at 10:06 AM on May 26

Dogs and bears are genetic cousins, much like people and chimps. It's a slight bit more remote than housecat/lion, but one could argue that "bears are dogs" or "dogs are bears" already.
posted by unixrat at 10:15 AM on May 26

The biggest dogs are definitely already in the black bear weight class.
According to Guinness, the largest dog weighs 282 lbs. Wikipedia says black bears weigh on average between 155 and 600 lb.
posted by cgg at 10:17 AM on May 26

Argh, me no type good.

If you had said "How many generations would it take to breed a cat as big as a lion?", people would say "A lion is a cat, ergo zero."
One could almost argue the same thing for dogs-bears. "How many... dog as a bear?", people might be able to say "A bear is a dog, ergo zero."
posted by unixrat at 10:18 AM on May 26

You can get a dog as big as a bear, in fact, Dire Wolf (Canis dirus) (American megafauna existing 1 million - 10,000 years ago) was 5 foot to the shoulder. The largest bear today, the polar bear is also 5 ft at the shoulder. An American black bear today is 2.5-3 ft at the shoulder.

The bear, on the other hand, would likely to be heavier and thus stronger, owing to the fat carrying that bears tend to do for food as a matter of course.

So it could happen - there's historical precedent. If you go for breeding programs, however, you run into problems because the dog becomes increasingly less fit to maintain the difference between its baseline and what you're selecting for, because you're only selecting for phyical attributes, like size, rather than other necessary things like food efficiency, bone-structure, heart size, and the thousand and one other tiny little details that evolution takes care of automatically. Also, you're using a much smaller breeding pool, for control purposes, which increases the risk of genetic problems.

By the same token, there have already been born very small chihuahua's (at 4-6 inches) that are smaller in length than elephant shrews (4-8 inches) - though obviously that's not the smallest shrew there is. Again, for any real successful change to pygmy shrew size (at 1-2 inches) that wasn't just an improbable mutants, you'd need to modify a great deal (stomach processes, food sources, bone structure) so you really are looking evolutionary time and not just the lifespans of two or three dedicated dog breeders.
posted by Sparx at 10:31 AM on May 26 [1 favorite has favorites]

Anecdotally: This weekend, I saw a full-grown chihuahua that was smaller than an average pet/lab rat. Its owner held it in the upturned palm of their hand, and there was still plenty of room that, if the dog fell over on its side, it would have still been in the person's hand. It was a freaking tiny dog. I suppose it could have been a puppy, but it didn't look puppy-like, it looked like somebody shot a normal-sized chihuahua with the Honey, I Shrunk The Kids gun. I wasn't part of the dog-showing-off, just a passerby, but in what I overheard the owner didn't indicate it being newly born, and it sounded like they've had the dog for several months. This tiny chihuahua's head was disproportionately large, as most chihuahuas seem to me, which could be a limiter on their smallness - dog brains may simply be too complex to shrink.
posted by AzraelBrown at 10:36 AM on May 26 [1 favorite has favorites]

(NB: After seeing another couple of answers, I shall point out I'm talking in size of conceptual averages- sure there have been 8ft11 humans but when you talk about how much controlled breeding it would it take to get 9ft humans I think you're asking a different question)
posted by Sparx at 10:37 AM on May 26

To answer the question in the spirit of it, you could probably breed a dog as large as the largest mammal which has ever existed. But let us instead use an elephant for shorthand, since I do not know the name or the size of that largest of mammals.

Starting with your average dog, my guess is that you could see a lot of growth in the first few generations. Within ten, you could probably hit mastiff size. You'd also start noting a decline in lifespans of the animals in question.

After you hit dogs in the 200-300 pound region, you'd see a slowdown in the growth rate. At this point, you're struggling against fundamental dog engineering (although the canids are remarkably plastic).

*reaches behind himself for some digits* After thirty-odd generations, you'd still get growth, but it might be slow. You'll have already selected for nearly every extant allele (genetic variation inherent in dogs) that contributes to having a Big Frikkin' Dog. At this point, you are waiting for the odd mutation to kick in to get Big-Dogs. Big hearts to go with very big dogs. Disproportionately thicker legs and spine. Increased vascular sturdiness. Delayed growth patterns, maybe.

At some point during this project, however, you might thaw yourself out from the generation-hopping cryonics bed and look at the creature and ask "Is this still dog?" A good way to prevent this project from branching into a new species dog-plus is to begin a delayed breeding program as such:

1) Harvest sperm from prospective big-dog males.
2) Take half your sperm sample and use it to fertilize eggs from basic dog stock. Store the other half.
3) Implant fertilized eggs in big-dog.
4) Take the resulting young and make sure they can interbreed with each other, with normal dog stock, and with your big-dog.
5) For those young which produce viable offspring, track back to that stored sperm sample and use that for another generation.

We like this method because 1) sperm is easy to obtain and store, 2) we do not want giant hybrid puppies growing in tiny basic dog stock, which would not only be cruel, but it would result in a lot of dead puppies which are therefore unavailable for test breeding.

Naturally, this method isn't perfect, but it goes a long way to making sure that your species is still dog at the end of the day.

I'd just idly guess and say a couple of hundred generations might get you dogs which you can breed back and whose average size is that of a middling bear species.
posted by adipocere at 10:46 AM on May 26 [9 favorites has favorites]

This Science article suggests that most size variation in dogs is due to just a few genes (or maybe just one; I'm not much of a geneticist, so I don't entirely grasp the details.) It seems as though the range of size variation which can be achieved by variation in these genes may have come close to its limits in modern dogs. If that's the case, to achieve further change, you might have to wait for more mutations, ones that will change the dog body plan significantly enough to let the dog live at the size of a shrew or a grizzly--you'd probably need significant qualitative changes in skeletal structure and/or metabolism to accomplish this.

So, it's hard to say exactly how long it would take, because you'd need to wait around for the right mutations, and you would probably have to occasionally breed in some dogs from other lines of less extreme size to keep your population from getting too inbred. I think it's probably possible, but it might take thousands of years, and what you end up with might not be something you could really call a "dog" anymore.
posted by fermion at 10:46 AM on May 26 [1 favorite has favorites]

Adipocere, the largest mammal ever to exist still does. Hello blue whale.
posted by merocet at 10:51 AM on May 26

Large dogs generally have shorter lifespans than medium and small dogs. Would this complicate the whole theoretical BIG DOG breeding program?
posted by elsietheeel at 10:53 AM on May 26

St. Ives Museum in Cornwall (UK) has a tiny stuffed dog (called Tiny of course) that, through some mutation or other, was fully grown at four inches long. If I remember correctly it looked somewhat like an english pointer, and was in perfect proportion.

Unfortunately other details are hazy, and there seems to be little mention of it on the web.
posted by le morte de bea arthur at 10:57 AM on May 26

So basically, the answer is that a Mastiff is already about as big as a dog can get unless you're talking about mutations and evolutionary time scales?
posted by empath at 11:00 AM on May 26

Sparx makes useful points about historical dog size precedent achievable via evolution and the problems with trying to get large through breeding instead, so unless anybody has info about a breeding program that attempted to breed ever larger dogs and had to give up after a while due to untenable problems in the dogs, there may not be a good definition of the upper limit from a breeding standpoint.

But if your other question is how quickly can you get from size A to size B, does anyone know how long it took to breed to some of the cited sizes or known breeds from a starting point? Is there anything in the historical record of dog breeding that notes the size of starter dog stock and the ending size of a particular desired breed and how long that took in an uninterrupted program?

This article contains some tangential info on evolution and breeding of the various types of dogs:
posted by Askr at 11:09 AM on May 26

For reference, the biggest shrew is about .22 lbs (that's the house shrew or Suncus murinus), according to wikipedia. Apparently the current smallest dog (by weight)--that's "Ducky", a Chihuahua--is 1.4 lbs. So in relative terms there'd be a long way to go, and a hell of a lot of generations of good luck, given how delicate these dogs are.

Just FYI.
posted by supercoollady at 11:10 AM on May 26

Oh, and just for further useless information, elephant shrews are not shrews. In spite of the profoundly misleading name, they're actually not even related. Funny world, this.
posted by supercoollady at 11:15 AM on May 26

I doubt that dogs can get much smaller than they already are - as it is, Chihuahuas and Yorkies aren't the most robust breeds to start with, and the recordbreakers for "world's smallest dogs" never seem to live for very long - they show up in the news as soon as they get confirmed at around a year old, and then a few years later you hear about the latest little guy, wonder what happened to the previous contender or three, google them, and find out that they're dead. Yipe. An excellent example of this: the smallest dog ever recorded was a Yorkie named Sylvia (1943-1945) of England, who weighed in at 4 ounces, stood 2.5 inches tall and was 3.5 inches long.

Since supercoollady beat me to all the other entertaining biology facts, the largest land mammal to ever have existed was the Paraceratherium (also known as Indricotherium or Baluchitherium), a rhino that lived 30-20 million years ago. Given that blue whales are the largest animal ever to have lived (and thanks to us they're endangered - aren't we awesome?), it seems sort of unlikely that we could breed a dog that big. They're probably as large as they are because they can support their weight (recorded as large as 177 tons - twice as heavy as the estimated weight of the largest known dinosaur) in the ocean.

That said, a 180-ton dog would be pretty badass.
posted by bettafish at 12:17 PM on May 26

You might find Wiki's entry on bear dogs interesting, either closely related to bears or an earlier species in the Caniformia suborder (which includes bears and canines).

The potential issues of rapidly increasing the size by only selecting for size have been brought up compared to natural evolution which includes the other traits to support such a size healthfully. Canines already show the most variation among size, at least among adult mammal species, as far as I know. So it seems likely that, given enough time, dogs could be bred approaching the size of the larger bears. They will also probably look a lot more like bears, with similarly stocky bodies and heavy skeletons to support the extra mass.
posted by 6550 at 12:36 PM on May 26

If you had said "How many generations would it take to breed a cat as big as a lion?", people would say "A lion is a cat, ergo zero."
One could almost argue the same thing for dogs-bears. "How many... dog as a bear?", people might be able to say "A bear is a dog, ergo zero."

Except that while Lions and tigers are cats, bears are not dogs. Bears split off from dogs almost 20 million years ago. Bears and dogs are Caniforms an order that contains not only bears and dogs but also raccoons, otters and sea lions. Also, the largest Caniform is The Elephant Seal.

Wikipedia has a helpful Phylogenetic Tree which of Carnivora (the even larger group that contains bears, dogs, cats, weasels, hyenas etc.
posted by delmoi at 12:50 PM on May 26

Oh, and just for further useless information, elephant shrews are not shrews. In spite of the profoundly misleading name, they're actually not even related. Funny world, this.

Thanks for clearing that up. I wasn't up with actual shrews as much as meta fauna and so I appreciate being corrected. No seriously!
posted by Sparx at 3:39 PM on May 26

As for small dogs, a friend of mine is a chihuahua breeder, and I recall that she doesn't feel that a dog under 4 lbs can reliably maintain a steady blood sugar level.She always carries snacks for puppies who haven't hit that mark yet, to keep them from getting hypoglycemic. I do know that raising the topic of people breeding for adult dogs to be smaller than that weight is a good way to hear a colorful string of creative profanity from her.
posted by Lou Stuells at 4:05 PM on May 26

These are the biggest dog breeds around at the moment:

Irish Wolfhound: weight: 105-125 lbs. height: 35-35 in.
Great Danes: weight: 100-120 lbs. height: 28-32 in.
English Mastiff: weight: 175-190 lbs. height: 27.5-30 in.
Neopolitan Mastiff: weight: 150-180 lbs. height: 26-31 in.
Newfoundland: weight: 130-150 lbs. height 28-30 in.
Saint Bernard: weight: 150-200 lbs. height: 27-30 in.

These are animals that have been bred for size for many generations; although a poster above said "After you hit dogs in the 200-300 pound region, you'd see a slowdown in the growth rate" I believe he's speculating wildly and has no firm reason to believe that selective breeding from an average-sized dog would rapidly produce dogs around twice the size of the biggest dogs ever seen in all the millenia that people have been breeding dogs. I would disregard the rest of his answer two, especially the parts where he admits he's pulling digits out of his ass and idly guessing.

I will reiterate what Sparx said above: the largest dog relative on record, the Dire Wolf, might well be the theoretical limit, but with the current genetic pool available to dog breeders, the largest current breeds are likely the biggest you could get. Mastiffs only live for 9–12 years, probably because their great size is bad for them.

I don't what would happen if you crossed eg Irish Wolfhounds with English Mastiffs to get maybe a healthier hybrid taller than a mastiff but with a heavier frame than a wolfhound, select for healthier animals with long lifespans, and then cross those to similarly-derived Great Dane/Saint Bernard hybrids. This might bring a lot of different big dog genes together in animals much less inbred than current pure breeds, and thereby give you a healthy big dog gene pool to start selecting for size all over again. As a geneticist (but not a dog breeder!) this is how I would go about trying to make bigger dogs, but I am not going to pretend that I know whether this method would produce bigger dogs than currently available, what size you would max out at, or how long it would take.
posted by nowonmai at 4:22 PM on May 26 [2 favorites has favorites]

In terms of the smallest, I can give you a small insight based on mouse work. (Lab) mice that are deficient for Insulin-like growth factor weigh 75% less than normal mice. This, I have been told, is pretty much as small as a mouse can get and still be alive.

If the same held true for dogs, the theoretical limit would be 25% of the smallest known dog. However, it's very possible that the smallest recorded dogs actually have/had growth factor hormone defects, and therefore are/were at the absolute size limit.

I should point out that breeding for small size would probably be selecting for genetic defects (aren't all that uncommon, they're just mostly recessive). Thus, it really isn't that different from genetic engineering (where you target the location of the mutation) except in time scale. If you continued to cross worlds smallest dogs together and selected the smallest progeny for further breeding, you would get new record holders, probably only after a couple of generations. You'd have to keep it up for a very long time (over a 100 years) to see where the plateau occurred.
posted by kisch mokusch at 4:26 PM on May 26

This might bring a lot of different big dog genes together in animals much less inbred than current pure breeds, and thereby give you a healthy big dog gene pool to start selecting for size all over again.

It wouldn't help. The genes that make those big dogs big are pretty much the same for all breeds (as mentioned above). And the health problems that make them die young are caused by the same mechanisms. An example, large dog breeds all have very high risk of osteosarcoma at a relatively young age. This is because the large amounts of insulin like growth factor that allows them to grow that big can also stimulate their bone growth to continue when it shouldn't leading to cancer. If you had a dog with a new mutation that caused it to grow that large despite normal IGF levels then sure, that problem at least would go away. But it's biologically unlikely and not what has happened with current big dog breeds.

Cross breeding between a few inbred breeds doesn't actually lead to hybrid vigour, which is why designer breeds like labradoodles annoy me so much, so to get the changes in size that the OP is looking for I think you'd be better off starting in the middle and working out again rather than trying to optimise the already flawed dogs we currently have at each end of the spectrum. And even then we really need new mutations to solve the current set of problems inherant in the very big or very small dogs.
posted by shelleycat at 5:08 PM on May 26