There seems to be more diversity in size shape and colouration between different breeds of dog than for any other species I can think of. Do people know why this is? And does this reflect some sort of underlying diversity in their genetics, or is it just that dogs have been bred more aggressively (and for longer) than other species?
As I understand it, it’s because the way dogs develop makes it easier to breed large, obvious differences in shape into them. Many of the differences you see in dogs are due to differing types of neonatalism*; the retention of juvenile traits into adulthood. Puppies have a greater difference in shape and appearance from adult dogs than (for example) kittens compared to cats, so it’s easier to make dogs that look seriously different in body, ear and muzzle shape.
- Examples of neonatalism: humans are shaped rather like baby chimpanzees, many ground dwelling birds are shaped like oversized chicks.
Yes, it is not so much that they have a great deal of genetic diversity, it is more that the ways their differences manifest are very visible. It is just variations in growth rates (snout long? Snout short? Legs long? Legs short?) which produces such a range of body types, nor basic genetic programming.
A species with seven blood types probably would have greater genetic diversity but you could not tell that from visual inspection.
Not long ago, a specific gene was identified that divides dogs into “large” and “small”. This seems to have been one of the first variants that was used by breeders to begin the process. It’s true that dogs have more phenotypic variation than just about any other species, and it’s not fully understood why, but it doesn’t necessarily take a lot of genetic variation to produce a lot of phenotypic variation, so I don’t think we can make that conclusion. It wouldn’t be surprising to find that there are only a handful or so of genes involved.
And yet somehow a bichon recognizes a lab as a fellow member of the ass-sniffing club when out for walks. Amazing.
“A dog is that which is recognized as a dog by other dogs”
-definition by Mark Twain
One item I read sais that the dog grwoth rates were turned on and off by different sets of genes at different times. Hence, you could make a daschund out of a rotweiler by selective breeding for the genes that forget to tell teh legs to grow. Ditto for the snout as mentioned above. This is, I think, the aspect of neonatalism that is more prevalent in dogs than most other species.
I also suspect that dog breeds have picked up a lot of donated genes from wild dogs of various types around the world. Eskimos for example, were known for staking out their huskies to be bred by wolves from time to time. Both Alsatians and Huskies look very wolf-like. So if the original pet dogs came from a very small gene pool of first-domesticated animals, I bet they got plenty of external donations as they spread around the world.
However, the process of creating a pure-bred inherently limits genetic diversity, since it involved a lot of inbreeding to make various traits dominant. I suppose the only saving grace of the dog’s genetics is that there are so many different pure-bred types and a wide variety of mongrels to add the occasional refresher.
This was on Nova Tuesday night. Even at the species level, it often isn’t so much a matter of different protein-coding DNA sequences so much as it is differences in the gene expression/ regulation system. To use a sort of silly analogy, it’s like the difference between a soft-boiled egg and a hard-boiled egg: exact same ingredients and preparation method, only difference is length of cooking.
The vast majority of dog genes are found in wild wolves. The main difference with dogs is that they’re segregated out. Thus, the typical wolf will (for instance) have some genes which tend to increase size, and some which tend to decrease size, and they just sort of average out to normal wolf-size, while a chihuahua’s size-related genes are almost all for small size, and a St. Bernard will have mostly big genes.
My guess is that it’s all in selective breeding. I had written a thorough explanation before noticing that Wikipedia has a more concise and better informed version of what I was trying to say:
http://en.wikipedia.org/wiki/Dog
“Over the 15,000 year span that the dog had been domesticated, it diverged into only a handful of landraces, groups of similar animals whose morphology and behavior have been shaped by environmental factors and functional roles. As the modern understanding of genetics developed, humans began to intentionally breed dogs for a wide range of specific traits. Through this process, the dog has developed into hundreds of varied breeds, and shows more behavioral and morphological variation than any other land mammal.”
If there is something at the genetic level that pre-disposes dogs to variation, I would suggest that this too is an outgrowth of 15,000 years of selective breeding. It would be an odd coincidence if the one species out of thousands of mammals that best lent itself to domestication also happened to be the one with the most stretchy-shapey genes.
This is fairly typical of any animal species that have been domesticated for a long time, and bred for different uses.
Look at horses, and the differences between Shire draft horses and Shetland ponies or mini’s.
Look at cattle, and the differences between Texas longhorn beef cattle and Guernsey dairy cows.
And then look at cats, and the fantastic variety of breeds!
This, combined with their social behavior, intelligence and versatility made the species useful for a wide variety of tasks. Has any other domesticated animal been subjected to such intensive breeding? 15K years is also a lot of generations for a species that reaches sexual maturity at about 10 months.
The term you are looking for is “neoteny”. That can explain some of the differences we see in dogs, but not most.
Most of the differences we see in dogs have to do with genes that regulate other genes, not genes that code for proteins. So no, dogs don’t have an usual amount of genetic diversity.
Incidentally, there are dog genetic testing companies that can tell you what breed or mix your dog is.
I don;t have a cite, but I recall an explanation that very minor differences produce the variance seen in dog breeds.
;)They claim to be able to do so. How do you know they aren’t just making the same guesses as people familiar with dogs make based on observable characteristics? Or even getting it totally wrong?
I’m sure they use good science, but I do wonder why people would want to pay for a service like that. My best friend is the best dog ever. Why would I want to find out what inferior breeds he descended from.
Well, for one thing, if you knew you could try to breed more dogs with his wonderful qualities. Or at the least, if you wanted to get another dog, you might try to find one that’s similar. And that’s even aside from just simple curiosity.
I wasn’t fully serious, I just like to brag about my friend. But I’ve seen people disappointed by trying to reproduce a good mix. Dogs have personalities that go beyond breeding. I wonder how dog cloning is working out though.
Funny! I’m sure your dog comes from the finest breeding stock! According to the testing sites, a lot of people do it because they keep getting asked what kind of dog they have, and all they can do is guess. My father has a mystery breed dog he rescued in Mexico. He’s always wondered what kind of dog she is. She was sickly and nearly bald when he found her, but grew into something resembling a bearded collie mix. He’s delighted that he can now find out more about her.
Actually, it was reflecting on the various other domesticates that brought the question to my mind in the first place. Yes there are a lot of, for instance, cat breeds. But the biggest ones are only about twice the size of the smallest, and there’s also less variation in facial shapes, fur/hair types and probably personality as well (I’m willing to be corrected on that last point - I’ve only ever owned moggies)
I was originally discussing this with a FOAF the other week and it was his considered opinion that I was on drugs for even asking the question, on the grounds that there’s far more variety within breeds in the plant kingdom (he brought up brassicas, in particular). Which to me seems like a totally invalid comparison, but sadly I don’t have enough knowledge of biology to articulate just why.
Because they aren’t animals, and don’t competitively reproduce?
This has been the subject of serious research, and there’s apparently an answer.
It’s not just genetic variety in dogs; it’s also that significant genetic change can occur more rapidly in dogs than in other animals. The significance of “more rapidly” is that it’s feasible to make sweeping changes in the animals within human lifetimes.
I can’t remember the term National Geographic’s The Science of Dogs program used, but it asserted that canids (dogs, wolves, foxes) have some unusual property to their DNA which is somehow linked to the genetic variation in dogs (something about repeating sequences…aha, I found this pretty well-summarized version while noodling around on Google:
excerpted from the Science of Heredity section of California Karelians. [Bolding and some typo corrections are mine.]
That website credits this Science Daily article as a source.