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Thread: Would Chihuahuas and Great Danes be considered separate species if all other breeds went extinct?

  1. #1 Would Chihuahuas and Great Danes be considered separate species if all other breeds went extinct? 
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    Can someone tell me whether my reasoning on this matter is sound. As I understand it, all the various breeds of dog, from Chihuahua to Great Danes, are currently by convention considered to be the same species. Even though it is virtually impossible for certain breeds such as Chihuahuas and Great Danes to interbreed with each other (if the Chihuahua was female it would die, and if it were male it couldn't impregnate the female Great Dane), because both breeds can interbreed with various medium-sized breeds, their genes can still flow back and forth (put very crudely, of course).

    However, what would happen if all of a sudden every other breed of dog went extinct, and all we were left with were pure-bred Chihuahuas and pure-bred Great Danes? Would the fact that these two populations, at least if left to their own devices with no human intervention, would be reproductively isolated from one another then mean that they would have to be considered to be separate species? Personally I've always felt that by all rights they should be considered different species now simply because they look so different from each other, not only in their fur but also their anatomy and skeletal features. But I know appearance isn't everything in biology.


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  3. #2  
    Life-Size Nanoputian Flick Montana's Avatar
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    While all dogs are of the same species, c. lupus, and descended from the gray wolf, we more than interfered with the natural evolution of the dog. They would still biologically be the same species and their off-spring (ignoring physical difficulties) would still be viable.

    Granted, if the only dogs left in the world were Chihuahuas and Great Danes and mankind didn't interfere in their survival, dogs would probably go extinct. Still, that doesn't affect their biological background and ancestry. It just means that we encouraged certain mutations to the point where the two breeds probably wouldn't be able to continue their lines.


    Last edited by Flick Montana; September 1st, 2012 at 09:16 PM. Reason: gray fox? too much skyrim
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    Then what would make them truly separate species? Because in that particular situation, it does fulfill at least some of the requirements for being considered its own species.
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    Life-Size Nanoputian Flick Montana's Avatar
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    Well, they are capable of producing fertile offspring. If you're trying to break the species designation by arguing that physical constraints prohibit reproduction, I would suggest that is more a product of our mutating them to the point where breeding is unlikely.

    The point I think you're trying to make is not one that is unknown to biologists. There has long been a species problem where defining the organisms proves difficult. For instance, if all organisms of the same species require the same ancestor, how do new species ever arise?

    The problem lies in the fact that it's just a naming system. Nature doesn't care how we divide up life, she works with her own methods. I think the issue you are experiencing is related to the taxonomy, not the biology, of the species problem.
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    Well, I feel I should point out that dogs/wolves and coyotes are able to produce fertile offspring with each other, and yet they are classified as different species, at least dogs/wolves and coyotes are, don't really know about wolves and dogs.
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    The current definition of species is imprecise. Lots of cases where different species are able to interbreed, yet still called different species.

    If the definition were tidied up, it would become an exact genetic definition. For example : two populations are considered different species if their genomes are different by factor 'X'. Maybe a percentage for a particular gene type?

    If such a definition were applied, making the science exact, the two breeds of dog would be clearly defined as the same species.
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    Alright, so I'm now going to ask my question another way. Have humans ever managed to breed any kind of animal/insect/fish/etc. to the point where it does become a different species with the original animal as its common ancestor, much like humans and Neanderthals are both descended from Homo heidelbergensis?
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    Brassica oleracea Strange's Avatar
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    Quote Originally Posted by Fanghur View Post
    Alright, so I'm now going to ask my question another way. Have humans ever managed to breed any kind of animal/insect/fish/etc. to the point where it does become a different species with the original animal as its common ancestor, much like humans and Neanderthals are both descended from Homo heidelbergensis?
    Yes. Observed Instances of Speciation

    I think an argument could be made that Chihuahuas and Great Danes are different species. After all, viable offspring isn't the only criterion. There are species which are almost genetically identical but are counted as separate species because they are geographically separate (don't ask me for an example because I can't think of one right now!)

    Also, I doubt that Chihuahuas and Great Danes could interbreed without assistance. In that sense they are reproductively isolated already.

    We consider them the same species for practical reasons. It is analogous to language. We consider Indonesian and Malaysian to be different languages for purely political reasons. We consider all the different languages in China to be "dialects" for political reasons. These are all man-made, and therefore, fuzzy groups.

    And, if adelady sees this thread, she may post one of her links to ring species...
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    Forum Radioactive Isotope skeptic's Avatar
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    Quote Originally Posted by Strange View Post

    I think an argument could be made that Chihuahuas and Great Danes are different species. .
    Only by jumping straight back to a non genetic definition of species. Rather a backwards step.

    Incidentally, the human/neanderthal distinction is not clear cut. Many anthropologists and geneticists regard the two as sub species - not distinct species. So we get Homo sapiens sapiens as distinct from Homo sapiens neanderthalensis. Distinct only at the sub species level, but both part of the same species.

    On two species closely related but geographically separated, I suggest the South American jaguar (Panthera onca) versus the African leopard (Panthera pardus). Those two are very similar, and occupy pretty much exactly the same ecological niche, but separated by an ocean.
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    Life-Size Nanoputian Flick Montana's Avatar
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    It can be difficult to apply a naming system to something that was not set up for a naming system. Defining species is still an ongoing topic of discussion among biologists so don't wrack your brain trying to figure it out.
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