Home Page › Forums › Darwin’s Ark › science question — atavism, reversion and pariah morphs
- This topic has 2 replies, 2 voices, and was last updated 4 years, 6 months ago by Jennifer.
November 12, 2018 at 7:23 pm #7049
There’s an idea I’ve often seen referenced online (Reddit, Quora etc.), usually in the context of discussions regarding an alleged tendency of megamutts to resemble “primitive” dogs, and especially to resemble the “Dingo look” (tawny, midsize, short-coated, prick-eared, with a “wolfy” head). Often these discussions will start with someone expressing curiosity as to why so many of the street mutts they saw in [name of some developing-country megalopolis] had this look. And the prevailing answer always seems to be “When dogs of all different breeds are allowed to randomly mix together, the resulting dogs revert to the original dog type, this is called a pariah morph” or something to that effect. Sometimes the answerer will even use phrasing like “morphs into,” which to me sounds like a misuse of the term (my understanding was that calling a dog a “pariah morph”–a term coined by Dr. Brisbin of Carolina Dog fame, AFAIK–simply means you’re observing that the dog looks like a Dingo, not that you’re implying anything about WHY it looks like a Dingo).
This idea has always seemed to me to have a suspicious whiff of magical thinking about it, but it’s not like I have a better answer, so I usually just frown in puzzlement and move on. But recently, I saw someone respond to one of those “why do so many megamutts seem to tend towards the same look” questions with a direct quote from a 1989 AKC Gazette article by Ian Dunbar. That got my attention, since Dunbar is a well-known and well-credentialed source, not only a veterinarian but also an animal behavior PhD. The quote was:
Now, if four dissimilar pure-breeds e.g., Lhasa Apso, Cardigan Corgi, Saluki and Newfoundland, were allowed to interbreed willy nilly, within just two generations, the mixed-breed offspring would largely resemble shepherds, Labradors, huskies and terriers types, even though these dogs have had no shepherd, Lab, husky, or terrier blood in their veins for hundreds of generations. This phenomenon is known as atavism, whereby the interbreeding of highly selected strains causes a reversion to the wild type, i.e., wolfy-lookalikes (shepherds and huskies) and prototypical dogs (Lab-pointer types).
He seems to be using “atavism” here very similarly to the way I’ve seen others use “pariah morph” (he even specifically raises the idea of “reversion”). But this quote puzzles me too, because I thought “atavism” referred to the re-emergence of a trait that’s otherwise been lost to a species through evolutionary change–like the way early carnivores’ rear double dewclaws have re-emerged in certain dog and cat breeds, despite that trait’s absence in wild canids, wild felids, and the earliest true dogs and cats. I don’t understand why that would even apply to his hypothetical, since between them its founding breeds already express all the traits needed to explain descendants looking as he describes (Corgi prick ears, Lhasa curly tails, Corgi and Saluki pointy heads, regression to the mean on height, etc.).
TL;DR — Is there anything to the idea that “atavism”/”reversion”/”morphing into a pariah dog” are required to explain why street mutts in many places often have the “Dingo look?” Or is it more likely just a question of, those are the traits that happened to be most common and/or dominant in these dogs’ ancestors (whether we’re talking the original founders of that population, or more recent infusions), and so that’s how their descendants tend to look as well, nothing particularly remarkable or hard-to-explain about it? I’ve always leaned strongly towards the latter, but I’ve seen this “reversion/pariah morph” explanation soooo many times now online that I’m starting to wonder if I should give it more credence.November 13, 2018 at 5:00 pm #7056
Thanks for your thoughtful question. I think this idea comes from a misunderstanding of what a pariah/ village dog is. There is this idea that all dogs come from our pet population dogs and that all dogs are mixes of breeds. In reality a vast majority of the world’s dogs are free-living animals that were never any breed. Those dogs as you mention have a certain look to them, (we have a nice blog article on this entitled “What is a dog breed”). This look is due to natural selection as well as some random events, for example if the founder of a new population has spots or floppy ears and they are not deleterious those will occur at a high rate. If a pure bred dog strays into the village dog population, it’s traits tend to be less well adapted to this environment and will be selected against and quickly swamped out by those of the better adapted local village dogs. There is actually a village in Venezuela that the Coppinger’s write about in their recent book “What is a dog” where they let St. Bernard’s breed with their village dogs, to try to make them look more like the famous war dog Nevado. Of course, the St. Bernard is much too large to be well adapted to surviving as a village dog in this area and while a few of their village dogs have some St. Bernard traits for a time, they do not survive as well and do not produce as many pups as the regular village dogs, so without continued reintroduction of St. Bernards their village dogs look like the normal village dogs from anywhere else in that climate.November 14, 2018 at 6:12 am #7058
Thanks, Kathryn, for the informative answer. I’ll have to add that Coppinger book to my reading list. I’d never thought about it quite that way before…that if you’re conceptually lumping all non-purebred dogs in the world into one arbitrary “mongrels” category, you’ll probably tend to come up with some pretty far-fetched theories trying to account for the tendency of longstanding “pariah” populations to look a certain way. I think it was that Dunbar quote that really threw me for a loop, because I thought, OK, well here’s someone with serious credentials, and even he seems to be saying there really is some sort of “reversion” effect intrinsic to mixing different breeds that’s destined to generate a “primitive”-looking population in pretty short order. To be fair, the quote is 30 years old, and in context he was discussing the unreliability of breed ID in bite statistics, not trying to explain why “village dogs” look the way they do. Still, I find it hard to read it as anything other than implicit support for the “mutts morphing into pariahs” scenario, and indeed that’s why the person I saw post it chose to cite it. Of course, it’s completely true that housepet-descended “First World” shelter mutts, like many of us own, often have no overall resemblance to any breed in them, and also that the loss of “type” relative to their purebred ancestors tends to be especially pronounced when those ancestors were phenotypically extreme (which seems to be a theme with Dunbar’s chosen example breeds). But at least to the best of my limited understanding, that’s not because these mutts are “reverting” towards any particular predestined form or forms, and certainly not because natural selection was substantially in play for their near ancestors.
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