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Is dog breeding evolution?

  1. Feb 2, 2008 #1
    I want to clairfy something: Is it true that without DNA mutations it would be impossible to start with a population of x wild wolfs and breed a chihuahua, or poodle?

    Lets say your only goal is to start with a very large population of wolfs who on average weigh 100 lbs, your goal is to create a dog that has an adult weight of 5 lbs, and lets say you are controling the evironment ect, so that no DNA mutations would occur. Would it be impossible to create a dog of that size unless you started out with a dog that size?

    Assuming no mutations if you start with a trillion wolfs and divide the population into a billion groups of 1000 and breed the smallest male and female from each group and they had 10 puppies each and you continued this until you were down to a final group siblings of puppies with the same parents is it possible that the smallest wolf could be 5 pounds, even though the smallest from the original trillion was say 80 pounds? It seems possible if each generation got smallest size set of contributing genes from each parent. Like if generation 1 got the combination of genes from their parents which is as small as possible, so that if you compare the size contributing genes of the father and mother and pick the ones from each that will contribute most to small size (one parent may be genetically bigger overall but they may have certain genes which contribute more to small size than the other parents versions of those genes).

    This would require that the genes for a 5 pound dog were somewhere in that origional population although they may be scattered amongst thousands of dogs.

    Is this how dog breeding works, because I find it improbable that enough mutations could have occurred to say create a chihuahua or poodle, in the 10,000 years since dogs first became domesticated by humans.

    Another question: is it possilbe for 2 siblings to get an identical set of genes from their parents, without being twins, for example two siblings born years apart which got the same exact genes? Do you know of an example where this has happened?
     
    Last edited: Feb 3, 2008
  2. jcsd
  3. Feb 3, 2008 #2
    Its chihuahua, sorry, just buggin' me. I would think that it is basically evolution, just a selective form of it.
     
  4. Feb 3, 2008 #3
    There I changed it.

    Does anyone who is an expert know the answer to the questions I asked?
     
  5. Feb 4, 2008 #4
    I would have though an expert on evoltion woul dbe quite hard to come across. I don't think of it as any natural form of evolution, as there is no selection between mates, and they do not evolve to better thei chances of survival.

    I think the fact that they are domestic pets would suggest that the evolution you are talking about isn't the same as natural evolution. I myself am not 100% so yes, if there is anyone clued up on this please try an explain :shy:
     
  6. Feb 4, 2008 #5

    Andy Resnick

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    I don't understand why you exclude mutation from a selection/evolution process. Mutations occur spontaneously all the time, and humans at least have huge numbers of single nucleotide polymorphisms (SNPs). Environmental pressure can drive what mutations are favored, but mutations are not *casued* only by the environment.
     
  7. Feb 4, 2008 #6
    Dog breeding is "selective" in most cases. Selective breeding and natural selection are two different things.
     
  8. Feb 4, 2008 #7

    Andy Resnick

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    Are they? It seems to me that the concept is the same. Certain traits correlate with increased survival and reproduction.
     
  9. Feb 4, 2008 #8
    The reason I excluded mutations, is because my specific question is how far could an animal be changed with pure breeding. If your goal was to continue to increase a certain trait in an animal how far could that be increased without mutations, and whether their is some limit, and to increase that trait any further you would need mutations. I guess that isnt such an important question anymore, since I would assume that it would be possible, if the original population had the genes somewhere, but it would be extremely unlikely that those genes would all end up in one animal at one point.

    By the way you say that mutations happen all the time, are you talking about mutations that get passed down to the child? I always assumed that they were very rare, because otherwise most people would probably have all kinds of genetic problems, since if you pick a random gene which has been chosen by billions of years of trial and error, and change it then you are almost guaranteed to have made a negative change, and only maybe 1 in 10 million DNA mutations would be positive.

    And I agree, I think that breeding and natural selection are basically the same, you could see the environment of the domesticated dog as being such that it favored small size. Its still selection for a certain trait, only that trait is chosen by someone.
     
  10. Feb 4, 2008 #9
    The dogs aren't being bred to increase their chances of survival!!! I would agree with you if it occured naturally but this is dog breeding, it is selective breeing, dogs whos genetics cause then to be better at survival aren't bred with other one as a result of the ones who do not have the survival trait dying.
     
  11. Feb 4, 2008 #10

    chroot

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    The biological definition of evolution is "the change in alelle frequency with time." This is certainly happening in selectively-bred dogs, and thus it certainly counts as evolution. In this case, the "natural" selection pressures are being overwhelmed by human decision-making, but the biological result is evolution all the same.

    - Warren
     
  12. Feb 4, 2008 #11
    I am talking about natural evolution. As I am sure you are aware evolution is a pretty vague word, I am saying that in terms of natural evolution where ideas like "survival of the fittest" and "natural selection" come from, this is not what dog breeding is. The reason I say this is that it is human who are controlling it, it is not the surrounding environment that has any say in what happen in terms of how they evolve. The results of this give you two different things, one is adapted to its surrounding environment and it best adapted and the other as you say is being overwhelmed by human decision-making.
     
  13. Feb 4, 2008 #12

    chroot

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    There's no sense in trying to isolate "natural" evolution from "artificial" evolution, in the same way that there's no sense in trying to isolate "natural" chemicals from "artificial" chemicals.

    Dog breeding is performed by allowing only the best animals to breed. This is still "survival of the fittest," only the assessment of fitness is done by a human being rather than by an ecosystem.

    It's still evolution, either way.

    - Warren
     
  14. Feb 4, 2008 #13

    This is where I dissagree, dog breeding is performed by allowing only the best animals to breed, that tick the boxes of the dog breeder. An example would be image, or bone structure. These characteristics are not necessarily key in their survival naturally, as their life does not depend on it. I think it is important to isolate both natural evolution and selective evolution, as they are not the same thing. Your example of chemicals does not really have much similarity to the one of dog breeding I don't think.
     
  15. Feb 4, 2008 #14

    chroot

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    These characteristics are critical to their ability to reproduce, at least in the false "ecosystem" created by the human breeders. If they escape their pens, all bets are off.

    You're free to have whatever opinion you like, but the biological definition of evolution is clearly met in both "natural" evolution and in selective breeding. Your personal biases aren't relevant to that determination.

    - Warren
     
  16. Feb 4, 2008 #15
    What I am trying to put forward is that there are two types of selection in evolution that we are talking about. One involves natural selection and the other involves artificial selection. I can accept that the biological definition is that, but I don't see what is wrong with dividing them into atleast these two groups. I am not dissagreeing with the definition, but saying that natural selection is the reproduction of a species with certain traits which is attributed towards its ability to survive and reproduce. Artificial selection is for the good of the human, who intentionally breeds (dogs) seeking particular traits.

    I think you have shown that I was initially incorrect in thinking that evolution fitted into more than one catagory, but I still think that it is important to note that specifically in selection that natural and artificial both result in something different, an adaptation to either their environment or to what their owners seeks to achieve,
     
  17. Feb 4, 2008 #16

    chroot

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    Again, you're welcome to your opinion -- just don't expect anyone else to have the same opinion.

    - Warren
     
  18. Feb 4, 2008 #17
    I don't think you could everyone to have the same opinion on anything, so I wouldn't expect the near on impossible. Thanks for the insight I think I will look at this all in a different light, and maybe I should actually read a bit more into the topic. Thanks.

    So I guess getting back to the thread starters question. Yes it is evolution. :tongue:
     
  19. Feb 4, 2008 #18
    Yes, mutations happen all the time. If you were to compare any 2 chromosomes, about 1 in every 1,000 bases would be a SNP (Single Nucleotide Polymorphism) on average. Keep in mind though, that the frequency of SNPs are less within genes than they are in between genes due to gene conservation.

    Oh and BTW, people DO have all sorts of genetic problems. Many may be obvious, and much more probably not so obvious.

    On the subject of dog breeding though, I think dogs have a somewhat unique genome that allows then to vary in size fairly drastically. I would say that the variation we see in dog breeding is more a result of epigenetics, than it is what many of you would think of as "evolution". But then again, IMHO epigenetics is a form of evolution as well...
     
  20. Feb 4, 2008 #19
    There is nothing sacred about definitions, we can define a word how we like for our own purposes, provided we do so clearly and unambiguously.
     
  21. Feb 10, 2008 #20
    My 2 cents if you will:
    The original question regarding a hypothetical scenario in which you wished to obtain a distinct breed of dog that has a significantly lower average mass than its intial ancestors, without new mutations occuring, is an interesting question.

    Firstly though, you simply could not prevent mutations from occuring. Most mutations are the result of infidelities of the DNA copying process. These could not be prevented in large and only enviromental mutation inducing factors could be eliminated, which as we have established play a small part in mutation occurence. Nevertheless it is a hypothetical situation.

    Obtaining this distinct breed of lower mass dog without mutations probably wouldn't be possible. Such a drastic difference in average mass would most likely be the result of a number of mutations. But a less drastic result could be attained. Unique combinations of alleles that already exist in the population you see can have massively varying effects depending on what other alleles they find themselves with. Genes do not act singularily and in isolation. The effect of an allele in the phenotype is as much a property of its genetic enviroment (and for that matter the 'traditional' enviroment) as the protein it codes for (look into additive gene effect). So it is possible that alleles already existing in the population could be combined so a much lighter dog is produced over many generations scrutinised by the human breeder. For as I have alluded to: traits of the phenotype, mass in this instance, are polygenic (determined by a number of genes). Hence there are a suprising number of combinations of genes for a given trait, each producing suprisingly drastic effects.

    Hopefully that did not come across as an uninformed rant. As for this debate over what evolution is and whether we can distinguish between natural and artificial selection.... I understand evolution as the increasing adaptedness of a population over generations. This may appear to defy the idea that the artificially selected dogs are evolving, but as just stated there is a degree of plasticity in biological 'definitions' which may not be familiar to physical scientists. It could be said the dogs are becoming more adapted, as they are becoming more like what the human breeder wants, and that is their main selection pressure. So I would show little caution in calling both types of selection causing evolution.

    The OP asked a second question, regarding the likelyhood of genetically idnetical individuals arising. Possible - yes. Likelyhood - ridiculously unlikely. Lets just consider in short what would have to happen and the approximate probabilities associated with these events. Two identical gametes would have to be produced by two different people: one male one female conventionally. Without going into details this is close to impossible (but technically not). Given this highly unlikely event occurs, the gametes would have to fuse on two occasions. The chance of a particular pair of gametes fusing is another stupidly improbably event. The offspring would also have to be viable (another probability assigned here). These events may as well be assumed independent, so the probability of two identicals being born on different occasions is calculated by mutlipying all these very, very small numbers together; obviously we obtain an even smaller number. Given sufficient time though, even the most improabable event, if it occurs continuously, should occur. But the time required for something like this to happen probably couldn't be counted on two hands. Considerations also have to be given to the different genotypes of individuals and the limited number of copulations in an organisms lifetime. All in all this ain't ever gonna happen.
     
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