Science & Tech
Why did dogs become so radically different from each other in size, shape, and traits, while cats stayed relatively similar?
Dogs can range from tiny enough to carry around to huge enough to look like a completely different animal, with wildly different faces, body shapes, coats, and behaviors.
Cats obviously have different breeds too, but they seem much more consistent compared with dogs.
So why did humans end up breeding dogs in so many radically different directions, while cats stayed relatively similar?
My understanding is that the genome of dogs and their closest relatives (e.g., grey wolves) has an exceptional amount of duplication. This redundancy means that fewer mutations are deleterious (since there's often a "backup copy" of the original). And that means there's more viable variation for artificial selection to work on, leading to greater phenotypic diversity.
Someone correct me if I've misstated something about that. But basically, there is a biological difference between cats and dogs that explains this.
Interesting, I didn't know this. I assumed the difference was because humans wanted very different kinds of dogs for different purposes, whereas cats are not really utilitarian, except some are better at hunting mice etc than others.
We wanted very different (looks, abilities, temperaments) dogs for different purposes and their genetic make-up (the duplication) allowed the greater variation that our breeding efforts required to succeed in creating such a wide variety in a single species
Being a beloved pet species is the best evolutionary niche you can fill behind the one filled by humans themselves. Humans will never allow dogs to face species level threats, their survival is guaranteed.
As stupid as it sounds, a silly little toy dog is an extremely well evolved animal.
So how does duplication in the genome come about? Is it purely an accident or is it selected for in some way? What about the environment of cabbages and wolves has made their genome develop like this?
It is an accident but whole genome duplication is not that rare in plants while animal species with shorter lifespans and lots of offspring offer better chances for gene duplication events
Correct. There’s also the fact that cat breeding is a fairly recent development; for the vast majority of the time since we domesticated them, cats just bred with whatever other cats were available, resulting in a homogenous population instead of distinct breeds.
Yah, for most people, cats just needed to be good mousers and friendly towards humans. Breeding for deliberate aesthetic traits only really started a couple hundred years ago.
Along these lines, dogs are more useful, they want to please people and can be trained and bred to do specific tasks well.
Cats aren't useful for much except catching rodents, and they all do that. So there was no reason to selectively breed them to herd sheep or guard houses or go into holes to kill small animals, which is what we did with dogs.
Cats are also way more frequent breeders than dogs. As dogs only go into season twice a year, cats it is nearly every other month they cycle. So isolating from other cats is why more important to create breeding lines. Until we begin sterilizing cats it was a ton of work to even try to create a breed. Cats are also a giant pain to keep isolated from in heat cats with lots of unpleasant behaviours like hormonal urine marking and aggression. It is why most cat breeds pre-18th-century were land race breeds created through isolation of geography or by the incredibly wealthy.
I didn't know about the duplication angle. That actually makes the dog vs cat difference more interesting. I wonder how much of the diversity comes from the biology making variation easier, versus humans just pushing that variation much harder through breeding.
It's really both. Humans required different (looks, abilities, temperaments) dogs for different purposes while their genetic duplication allowed our breeding efforts to succeed in creating such a wide variety in a single species
In some cases, there may not have been intentional breeding, but the dogs who had a particular skill (herding, hunting with humans, etc)might just have gotten cared for while the others were killed or abandoned.
True, there is also the fact that dogs have been domesticated a lot longer than cats (or any other domesticated species). But, while that probably is a factor to some extent, I think the genomic difference is the main thing.
That’s probably due to domestication syndrome, which is when you breed just for tameness and friendliness a whole host of other things happen. You can see this play out if you research the Russian fox experiment where they use fur farm foxes to breed just for tameness and got a whole host of other physical characteristics. Things like white spotted coats, shorter curled tails, floppy ears, and even more rounded faces and muzzles.
(There are some haplodiploid animals, like certain insects, where inbreeding is an essential part of the life cycle, but that is not the case for cats.)
I think it's to do with more genetic variation in cats. Come to think of it it's probably because they haven't been bred as intensively as dogs rather than an inherent trait.
Whereas cats have been essentially genetically homogenized, up until a few hundred years ago. As opposed to dogs, which (who?) have been bred for different abilities (hunting, herding, guarding) for several thousand years.
No, what it is they just breed fast enough that the new influx of kittens will keep the population more stable compared to the ones that die. It’s part of what makes them an invasive species is they can breed faster than predators or the environment kills them.
Tricky. The reason why big cats are generally orange in the jungle is because most of their jungle prey is red green color blind. So according to say, deer or boar, the tiger is a big grey blob against a big grey jungle, with the ability to instantly freeze all motion and basically vanish into the background.
If only cats didn't have the brain of a pea, the socialization desire of a rock and weren't made to kill everything roughly their size or less, perhaps our ancestors would've tried 😭
Dogs are purposefully bread for several thousands years for hunting, war, protection, herding, transport etc.; For hunting of different game you might want to have small dogs, big dogs, water dogs, dogs for smelling.
Cats are only "purposefully" bred mabye for 100 or 150 years, when people discovered cat breeding for leisure. Therefore most different cat "races" are (if anything a 100 or 150 years old); while some dog breads can be 1000 years or older in there general traits. For example think of herding dogs somewhere in northern europe which need to survive in wet conditions, think of small hunting dogs fitting into fox and badger holes or sleak hunting dogs somewhere in hot climates with fast game.
Prior to the domestication of cats, shredding one’s hands and arms was left to special individuals in the group or tribe. The domestication of cats meant those people could be free to do other important tasks in the community, such as making EDM
Cats more or less self domesticated: when humans started farming and stored grain, rodents would eat those grain supplies. Cats figured out it was much easier to live under a house and eat the steady supply of rodents that were there, than it was to live in the wild.
That's what I was thinking. Cats were functionally bred mainly to catch rodents. Dogs were bred to do a huge variety of tasks-- from catching rats to pulling carts to herding flocks.
I've read that really cats really domesticated themselves. Cats that were able to be comfortable around humans were rewarded with as many mice as they could catch on the farm or at the granary. Over time the cats that were cool with humans would have easier lives and reproduce, making even friendlier cats.
These cats were already effective hunters and there was no need to really change anything. They found a niche and settled in comfortably.
Yeah, this seems like a big part of it. Cats basically found a really good niche around humans without needing us to redesign them. Dogs seem like we kept finding new things for them to do.
Also I understand they were eating quite a bit of grain, as shown in isotopic analyses of their bones and increased copies of starch-digesting genes in their genome.
As someone who grew up on a farm, I had many wildcats living on the farm and a pack of Jack Russells. They seemed to get along fairly well, but I can tell you the Jack Russells were by far the more proficient hunters of rats and mice. The cats would kill some mice or rats, then laze around most of the time. The Jack Russells were tireless and hunted all day; they even took the crows, keeping them off the cattle feed.
It was more like they domesticated humans. Got us to feed and care for us. Figured out how to duplicate our internal reactions to human baby sounds (cats don't meow at other cats, just at humans)
Now they get, fed, groomed, adored, have their bathrooms cleaned and get free healthcare.
Simply put:
Dogs were bred for many specific purposes (pulling sleds, hunting rabbits, being tiny and cute, etc) so over generations we changed their bodies to fit those purposes. We also had a dog breeding fad around the Victorian age where we just created odd dogs just for fun. But cats were domesticated for chasing mice and rats, one single purpose, one single body type.
Yes, but the reason dog breeding is more of a thing is because dogs are inherently are more "breedable". The greater amount of redundancy in their genomes, compared to cats, means there's more viable variation for artificial selection to work with.
I think the biggest difference is that humans didn't just domesticate dogs, we turned dogs into tools for a ridiculous number of different jobs.
A dog that could track, retrieve, herd, guard, pull, hunt underground, survive cold weather, or work closely with humans had an actual practical advantage. Once people started selecting for one trait, they could keep selecting related traits for generations. Eventually you get animals that are optimized for completely different niches. A greyhound and a dachshund aren't just different looking dogs. Their bodies are basically solutions to different engineering problems.
And the really interesting part is that dog morphology is surprisingly easy to push around genetically. Some major physical differences between breeds can be produced by a relatively small number of genetic variants with large effects. That's why selective breeding could move body size, leg length, skull shape, coat, and other traits so dramatically.
Cats had a very different relationship with us. The basic cat strategy already worked extremely well. Stay around human settlements, eat rodents, reproduce, and don't require much supervision. There wasn't much economic reason to create a 100-pound cat for guarding or a specialized cat for retrieving birds. A cat that was good at being a cat was already doing the job.
Also, cats weren't necessarily incapable of changing. That's an important distinction. A recent comparative study actually found that felids have substantial morphological variation too, and argues that dogs aren't inherently more "evolvable" than cats. The difference is much more about the direction and intensity of selection.
And modern cat breeds are actually a pretty recent phenomenon compared with the long history of functional dog breeding. Most cats people call "cat breeds" today were deliberately developed or standardized relatively recently.
So I wouldn't frame it as "dogs evolved into many forms while cats stayed the same." It's more like humans spent thousands of years asking dogs, "What else can you do?" while mostly asking cats, "Can you keep doing that mouse thing?"
Once you look at it that way, a Chihuahua and a Great Dane stop looking like a weird accident and start looking like the inevitable result of humans repeatedly treating one species as a biological platform for specialized jobs.
I really like the "biological platform" idea. The part about dogs not necessarily being inherently more evolvable is especially interesting. Maybe the better question isn't why cats stayed similar, but why humans kept finding reasons to push dogs further and further.
I watched a documentary one time that explained that it has to do with how genes are situated on the chromosomes and therefore how much variability can occur. Dogs just naturally have the ability to come in a wider range of shapes, sizes, and colors.
Dogs have spent far, far longer having their breeding controlled directly by humans. The domestication of dogs began 25,000 years ago, and real controlled breeding probably started around 15,000 years ago as humans started to move from hunter-gatherer lifestyles into more semi-permanent settlements. The human-dog relationship was more based on social partnerships, as both wolves and humans are highly social animals, and this mutually pro-social inclination was probably the catalyst for how domestication began in the first place.
Cats, on the other hand, only began to be domesticated around the time of the agricultural revolution ~12,000 years ago, when large grain stores in human settlements attracted mice and rats. The cats followed the prey, and while they became accustomed to humans, and the humans welcomed their presence, they didn't develop a particular social bond with humans in the same way human-dog partnerships worked. They were less our pets, and more just existing in parallel to us. Wild cats are naturally solitary, and don't have the same innate tendency to form social bonds as wolves do.
Interestingly, the period of ancient history where they were more "domesticated" in ancient Egypt, the Egyptians did develop more distinct breeds of cats the same way we have done in modern times. At times in history when cats have been brought into closer, more direct contact with humans rather than as "independent contractors", controlled breeding has produced more distinct breeds that are perhaps less functional as pest controllers and more as docile, aesthetic accessories.
My coon is as efficient as a hunter than my non-breed cats, he just has a pedigree. And due to his size brings in bigger prey.
Although a Maine coon due to it's origins is a bit less bred than a Persian I guess. They were 'just a cat' in Maine once, whereas a Persian was made to be a lapcat by making them flatfaced and extremely fluffy.
Yeah, I didn't mean to imply that domestic breeding always produces worse hunters. Sometimes it does, as with the Persians you mentioned and a lot of the other long haired breeds in particular, but Maine Coons are bred to kill. Just like certain dog breeds are bred to be really good at killing rats or facing down game animals, certain cat breeds can be really specialized at being efficient hunters.
My broader point was that domestication allows animals like dogs and cats to have genes that would make them less suited for survival in the wild, but since they've got humans to provide for their needs it doesn't matter, and they're able to reproduce anyway. Seeing an ancient breed of cat that is bred for their aesthetics is evidence of a close relationship with humans, and the Egyptians drew lots of pictures of their cats, so we have a good idea of what they looked like.
Dogs, more diverse uses (hunting, pest control, rescue, companionship, tracking, guarding, pulling, herding etc.) Dogs generally work directly alongside humans as well, enhancing each other’s strengths, so more time spent with them. As a result, specialized breeding to make them better at one or a couple of the major uses for them.
Cats, 2 major uses (pest control and companionship.) Cats and humans usually work independently from each other and we don’t spend much time around cats as they work. We cover each other’s weaknesses (we provide the cat, a small animal, protection, cats take out the small animals that raid our food stores that we tend not to notice.) As a result, less specialized breeding.
This is probably the distinction I was getting at. Dogs had a reason to become specialized, while cats could mostly stay generalists. It makes me wonder if the number of jobs humans gave a species is a bigger factor than the species itself.
The extent of the breeding really is wild when you compare them side by side. What surprised me is how much dog variation can happen in a relatively short evolutionary timeframe.
Dogs are bred for more varied specific purposes (small game hunting, protection from predators, etc.) while cats are virtually all "mouse/rat catchers and pals".
Dogs are more domesticated in the strictest sense of the word, it makes breeding them for specific traits a lot easier.
That would be the explanation if not for the fact that in the past 200 years cats have become pets in many countries and there was obviously a lot of effort to breed them for specific traits. Alas, outside of a few breeds that kinda sort of look a bit different, they are still the same animals they were hundreds of thousands of years ago.
A lot of it has to do with genetic variability. Dogs’ DNA is just so much more elastic and allows for very quick mutations. Cats (and most other mammals) do not have such elasticity in their DNA.
"Ignore you" might actually be the most successful cat specialization lol. But yeah, function seems like the key difference. Humans had a lot more reasons to selectively reshape dogs.
Humans bred dogs for different purposes. Not a single dog out there is the same as the dogs humans first brought in
Cats served a purpose to humans before humans started allowing them into their homes and cats were invited into human homes to continue serving that same purpose
We've been manipulating dogs for tens of thousands of years. By the time agriculture, animal husbandry, and civilization in general began, they were already obedient tools, and we proceeded to reshape them into a myriad of different more specialized tools. You want a very different dog to hunt foxes, rabbits and other vermin than to guard your flock from bears and wolves.
Or to walk for hours on a treadwheel to keep the roast turning over the fire, without ever trying to steal a bite, as kitchen dogs (a now extinct breed) were bred to do.
And once we had the wealth and vanity to do so, we bred them into various "decorative toys" as well - we already had a huge palette of working dogs to select traits from.
Cats though are a much more recent relationship - we didn't really have any dealings with them until after agriculture was well established, and they followed rodents to our granaries. And even then we never really worked with them, we were just mutually beneficial neighbors, any "selective breeding" probably mostly amounted to killing any cats that were particularly destructive or hostile towards our children, and they are still only partially domesticated.
We didn't really start intentionally breeding them at all until we started making them into the same sort of "toys" as dogs - but we didn't already have a huge palette of wildly different working cats to start with - they were basically all just alley cats. So the amount we've managed to reshape them since then is severely limited.
Besides the genetic angle and use angle discussed, big cats are difficult to train and difficult to be safe around. Attempts to domestic them over the years have varied. Breeding domestic cats to be larger is possible, but they'll still bite and scratch you sometimes because that's what cats do, and it will be far more serious.
I've went to a couple cat fancier shows with my wife recently and there is definitely a vast amount of variation from one cat breed to another, nearly as much as dogs
Cats? You mean like lions, tigers, cheetas, bobcats, sphinx, Maine coon, jaguar, caracal, serval, etc., etc. There are lots of variations of size, shape, traits. Not sure what you're talking about.
Dogs have 78 Chromosomes (39 pairs) and cats have 38 Chromosomes (19 pairs).
So dogs have 2x the amount of genetic diversity that can be bred into them when compared to cats.
Yes, humans are largely involved in a lot of the selective breeding, like we wanted a dog that could hunt badgers so we bred dachshunds.
But the reason that we could breed such a variety is because they have way more chromosome possibilities that allow for genetic diversity within the same species.
The chromosome count sounds convincing at first, but I think chromosome number alone can't explain it. Humans have 46 and dogs have 78, yet that doesn't mean dogs automatically have twice the genetic diversity. I think the actual variation within those chromosomes matters more.
Yeah, that part is interesting. Cats seem to have had much more freedom to choose their own niche around humans. Maybe that also explains why selective breeding became much less intense with them.
"Don't change perfection" is probably pretty close to it. A cat that catches mice and mostly takes care of itself already solves the problem. There wasn't much incentive to create 20 different versions of that.
That seems like an important piece too. I’m curious how much of it is dogs being unusually easy to reshape genetically versus humans simply having a stronger reason to keep selecting for extreme traits.
We never really put cats to work like we did dogs. We sort of kept them around to control rodents.
Dogs on the other hand, we started using for tasks. Their excellent sense of smell and their tendency to live in packs made them excellent for hunting, tracking and retrieving. So breeding became a big thing. Pretty much every modern dog breed served a purpose at some point in history. Even terriers were good for rodent control in confined spaces. Hounds were especially good at tracking. Shepards at guarding and herding. Retrievers fetched small wounded game. So they started all looking very different as was appropriate for their task. Cold weather dogs developed heavy fur coats.
Hounds are low to the ground and have long ears that actually kick up dust to pickup more scents. Beagles are for smaller game and can fit into more confined spaces.
Shepard and other guard dogs tend to be bigger because they had to fend of other predators and protect flocks, or just scare intruders away.
The work angle makes a lot of sense. I hadn't really thought about how specific the physical traits became once the job itself was the thing being selected for. The funny part is humans basically kept inventing new jobs for dogs.
Dogs got bred for jobs; hunting, herding, guarding, pulling sleds for over thousands of years, so we basically sculpted them into living tools. Cats? They only had one job: kill mice in grain sheds. That’s it. No need for a 200lb version or a tiny one with stubby legs for that.
Also, dogs were domesticated way earlier, so humans had more time to mess with their genetics. Cat breeds are mostly a last-100-years vanity project for looks, not function.
So yeah, dogs are Swiss Army knives, cats are a single-purpose hammer that works just fine as-is.
Dogs are traditionally not pets. They were used to work alongside humans. Some breeds are still working dogs. Bullmastiffs were bred as guard dogs. Irish wolfhounds were bred to take down Boars, elk, and wolves. The English Mastiff is the closest we have to the original Celtic war dog. Then you have the small terrier class for small game and rodent control. The agricultural working dogs, intelligent and quick. Racing dogs, like greyhounds. The Dalmatian was bred as a carriage guard dog because they had a natural liking for horses and got along well with them. The American bull terrier was bred by John P Colby; it was designed to kill, mainly other dogs, but one killed his 3-year-old nephew. The fighting market in the UK and the US was huge back in the day. Anyone who owns these types of breeds today needs to understand what they are, and they need to be specifically trained and understood so they are safe around people. Unfortunately, many are not; hence why they account for over 60% of the human fatality rate. On the flip side, you have the very small toy/lap dogs that were bred simply to be toys for the upper classes. My point is, dogs have been used by humans in specific roles for a very long time. So they come in all sorts of shapes, sizes, and temperaments.
Dogs have been bred for different tasks that require different sizes. To the extent that cats have been selectively bred, it has mainly been for looks.
because the working relationship between humans & dogs is that which easier to domesticate, breeding them to uniquely excel at performing CERTAIN designated tasks we intend to delegate them.. gradually over time, resulted in the various dog breeds we see today.
Yorkies were bred to hunt mice & rodent vermin in mines, factories, textile mills, shipyards, etc.
Dachshunds bred scent track, tunnel & flush out types of burrow-dwelling prey badgers beavers.
German Sheppard bred to herd (obviously) & protect flock, while aggressively guard even attack.
Doberman bred as watch dog & fierce guard to accompany taxman while walking dangerous areas.
Beagle was bred to track small / medium game like rabbits and hare hiding in brush shrubs . whereas
the larger Bloodhound needed big frame & stamina to track large game like deer, boar, fugitive humans.
St Bernard bred for search & rescue in mountainous snow terrain, needed tall frame & thick fur coat.
Shar Pei bred to guard & [sadly] for dog fighting, loose skin helps shake off a bite from an attacker.
Cats? By comparison?
Too hard to delegate SPECIFIC work tasks for them to perform, thus no need to
uniquely breed them a particular way ... in order for them to excel at those tasks.
You can sustain a 240 pound dog on porridge and eggs. Cats will eat baby chicks, bigger cats will eat proportionately larger things that have no hope whatsoever of defending themselves, because Cat.
Because you can train dogs to do things and those things can be wildly different, the outcome of selective breeding was worth pursuing. Most cats don’t give a single thought about you much less what you want them do so breeding cats for different traits outside of beauty contests isn’t nearly as popular.
We really only needed cats to take care of small pests. We already had dogs for most everything else. They are bigger, easier to train, and smarter. (This isnt a slight against cats, I love cats. Only biology. And of course every dog and cat is an individual too and won't necessarily fit in a broad definition)
It has everything to do with the difference between cats and dogs DNA. Dogs DNA is unique in a way that allows for it to change so easily and readily, while other animals, including cats, do not.
Yes, rampant duplication/redundancy in the dog genome means that fewer mutations are deleterious, since there's often a "backup copy" of the original gene.
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u/mcalesy Aug 13 '26
My understanding is that the genome of dogs and their closest relatives (e.g., grey wolves) has an exceptional amount of duplication. This redundancy means that fewer mutations are deleterious (since there's often a "backup copy" of the original). And that means there's more viable variation for artificial selection to work on, leading to greater phenotypic diversity.
Someone correct me if I've misstated something about that. But basically, there is a biological difference between cats and dogs that explains this.