Diversity Goes to the Dogs

Do domesticated dogs have the most diversity in physical appearance among those in the animal kingdom? If someone didn’t know better, they’d never guess that a chihuahua and a mastiff are the same animal. I can think of no other species where a healthy, normal adult can weigh, literally, 100 times more than a healthy, normal adult of the same species (not to mention the vast difference in exterior appearance.) And, how did they turn wolves into such a motley array of breeds? I know the short answer is selective breeding, but how do you get from a Saint Bernard to a Yorkie? Finally, what would happen if that Saint Bernard managed to impregnate that Yorkie? (With the help of modern science, of course.)

You don’t. You start with breeds closer in size and shape to your target and work from there.

Probably a difficult childbirth that would either kill the mother or the pups. The reverse might work, however.

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You don’t. You start with breeds closer in size and shape to your target and work from there.

I get that. Perhaps I should’ve written “how do you get from a wolf to a Yorkie?” or “a wolf to a Saint Bernard?”

There’s a fair amount of diversity in domesticated horses as well. Think Giant Draft horses - like Clydesdales vs miniature horses or Shetland ponies. Not as much diversity in facial features, but size difference is pretty comparable.

You breed only the animals that have characteristics you want. For a Yorkie, breed the animals that are smaller and have coat colors more appropriate to Yorkies. Keep breeding their offspring, and you are intentionally picking animals that tend to be smaller and smaller.

Selective breeding. Very selective breeding. Keep in mind that most modern breeds were only developed in the last 200 years. But we’ve been selectively breeding for thousands of years.

As for the diversity question, “yes” if we consider only mammals. You can find some crazy diversity in a single colony of social insects. Some species will have members with wings that can fly while others don’t. That’s some serious diversity there!

That isn’t clear. Dogs and wolves are closely related, but the divergence started a long time ago, there was a lot of recombination between dogs and wolves over that time. The various modern breeds were developed from ancient dog breeds that had a lot of variation already. From there the modern breeds were developed through inbreeding and mixing. So unless you begin by breeding wolves with dogs, it’s not clear that you could actually get a St. Bernard from a wolf simply through breeding. But since nature did something like that before, it could certainly happen with large enough populations and the ideal set of environmental conditions over a long period of time.

That’s not correct. All dogs are descended from wolves (with possible interbreeding with other canid species). Dogs are the same species of wolves, so it’s not like there was this dog lineage, independent of wolves, that were bred with wolves to get modern dogs. Dogs are wolves. Just a domesticated variety.

Indeed, we did get a St Bernard from a wolf through selective breeding.

Yes. That’s correct, but we don’t know if the path from wolf to domesticated dog was all a result of breeding.

Missed the edit window. Maybe I’m not being clear. We don’t know that the variety of modern or ancient dogs was entirely the result of selective breeding. Some of it may have been good old fashioned undirected evolution. It might not be possible to reproduce those conditions through breeding.

Ever see a really small adult person? Like, 3 feet tall? This is a single mutation that causes dwarfism. There are actually several different mutations that lead to dwarfism.

Toy dogs have the same sorts of mutations. It wasn’t just a matter of selecting the smallest pups out of litters of wolf-sized dogs for hundreds of years. People found random dwarf pups and for whatever reason kept them and bred them together.

So you can go from a wolf-sized dog to a lap dog in one generation, provided you get the correct mutation. All sorts of diverse dog traits come from a single mutation in one puppy that some breeder noticed and decided to preserve. And this is why dogs aren’t as genetically diverse as they seem, since most of these traits are simple mutations. Wolves have lots of genetic diversity even though they tend to look a lot alike.

Yes, but we’re pretty sure that the non-selective type didn’t produce the St Bernards and the Chihuahuas. At any rate, anything nature can select for, we can, too. It’s just genes.

Domesticated carp get pretty diverse - from giant koi (1.2m) to the weird varietiesof pop-eyed, fan-tailed goldfish (goldfish can reach 40cm so there’s a lot of variation there too). Koi and goldfish aren’t the same species, though - they can interbreed but the offspring are rarely fertile.

Yes, but dwarfism in humans not a reproduceable trait. Two dwarves do not necessarily produce dwarf offspring. But two cocker spaniels will always produce cocker spaniels.

Yes. Agreed. I’m not saying that wolves turned to St. Bernards or Chihuahuas through accidental evolution. But the intensive breeding that produced the modern breeds started with dogs that were already distinctly different from the general wolf population. The Irish Wolfhound, sometimes considered the largest dog based on shoulder height, is an ancient breed of unknown origin. They’re big enough to kill wolves by grabbing them by the neck and shaking. We just don’t know how much breeding and how much development in the wild created this variety of beast.

I’m not getting your point. There is no reason that we couldn’t take wolves, today, and turn them into St Bernards. It might take many, many generations, but there is no reason we couldn’t do it. If nature did it or nature + man did it, then man can do it without nature.

And by “nature”, I mean non-human influenced breeding.

I guess that could be true if you assume all mutations and variations of genetic composition can be reconstructed from breeding, and modern wolves contain all the genetic components that were in the wolf population at the time of the earliest divergence. With the first assumption you could eventually breed a St. Bernard from a fish.

That’s because random-bred populations that contain lots of varying alleles will be mostly heterozygous. To produce a breed that breeds true you have to fix the alleles you want and make them homozygous, that way every cocker spaniel will have two copies of the gene that makes floppy ears, and therefore every breeding between two cocker spaniels will produce babies with floppy ears. But if you breed a cocker spaniel with another dog, the pups won’t all have floppy ears, it might be that none of the pups will have floppy ears.

Some dog breeds have particular mutations that showed up at random, if those mutations don’t appear or aren’t recognized and preserved in your breeding population then you have no hope of reproducing the breed simply by selective breeding. Eventually you’ll probably find mutations that lead to similar or identical phenotypes, but you might never get the exact same single nucleotide polymorphisms that cause some dog traits, even though you might get mutations that have the exact same effect of knocking out a particular gene.