Monday, March 8, 2010

Artificial Selection

The domestic dog is an example of a species that has been "sculpted" into many different breeds. The difference between artificial selection and natural selection is that "it is the breeder rather than nature who sorts out which variants are 'good' and 'bad'" (Coyne, 127). Breeders can mate dogs with desirable traits to create just about any variation they would like. This selection extends to Coyne's examples of the wild cabbage and of the svelte wild turkey.

How come domestic dogs can exhibit such variation but still remain just one species?
How is artificial selection evidence for natural selection?
Give some examples of organisms that have been bred for a desirable variant and state their purpose(s).
In your opinion, is there anything wrong with humans imposing their will on the characteristics of other organisms? Why or why not?

5 comments:

  1. Domestic dogs have such variation because breeders have created certain breeeds to have certain features. The varying types of dogs are still considered one species because they have the ability to mate with each other. Artificial selection shows how humans can speed up the process of natural selection by picking select dogs to survive and reproduce, creating dogs that have specific traits humans have picked over a few generation. This shows how certain traits that are an aid in helping a species reproduce could lead to that triat showing up in the population many generations later. In the case of artificial selection, humans speed the process up by picking dogs with specific traits, while nature is a much slower process that solely results in survival of traits that help an organism reproduce. Examples of organisms that have been bred for a desirable variant are seedless grapes, seedless watermelon, and seedless oranges. All these fruits have been created because people do not enjoy eating the seeds of the plant. Breeders of plants created these variations by ensuring the plant reproduces. Eventually, the plants lost the seeds that would be used for reproduction because they were no longer needed since the breeders ensured successful reproduction. I think it is wrong for humans to impose their will on organisms because we are virtually changing the makeup of these animals to the point where they are no longer recognizable compared to their ancestors. The svelte turkey shows an example of humans changing the characterisitics of an organism to an excessive point. The svelte turkey has been bred to produce large breasts to the point that it can't stand due to the weight of the breasts. Humans become too controlling when the change the normal function of the organism they genetically alter.

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  2. The domestic dog diverged from the gray wolf on the path of evolution over thousands of years of domestication and training by humans. Using mitochondrial DNA, scientists have found that the two species first began to diverge 100,000 years ago, but the first true evidence of a growing relationship between man and dog can be found at a fossil site in Germany that dates back 14,000 years. Dogs developed a mutualistic symbiosis with humans; by sticking close to humans, dogs could ensure themselves of a steady supply of food, shelter, safety, and dogs of the opposite sex, while humans could benefit from the dogs’ fantastic sense of smell on the hunt and the warmth that the dogs could provide. Over the thousands of years that this relationship has existed, humans have selectively bred domestic dogs for various traits, in effect taking the “natural” out of natural selection. While this selective breeding has led to different sizes, appearances, and behavioral traits, all breeds of dogs are considered to be the same species because they can still reproduce with each other. Breeds of dogs are analogous to races of humans; each breed shares the same anatomical characteristics while containing outward features that distinguish it. Each breed of dog has characteristics that would have been favorable to the people domesticating it; for example, Siberian huskies have thick coats and wolf-like appearances that befit survival in the extreme cold of Siberia. A golden retriever or Yorkshire terrier simply does not have the outward features to survive in such a harsh climate, and thus those breeds would not have been useful to the native people of Siberia. As Coyne says in his book, “the criterion of reproductive success is human desire rather than adaptation to a natural environment” (127). Whether the humans of a certain region bred dogs for appearance, speed, aggression, durability, or any other characteristic, they selected for various mutation in canine DNA, which then became the norm for that particular breed.
    Many like to look past this fact, but there was also an effort to breed humans. The eugenics movement, which gained infamy under Hitler but also had followers in the United States, sought to breed humans for strength, height, and Nordic traits- blond hair and blue eyes. Hitler attempted to carry this plan out by rounding up all people who did not have these characteristics and sterilizing them so they could not pass their genes to the next generation. The ultimate irony is that Hitler himself did not have blond hair or blue eyes. Yet to think of this as a Nazi plot is to fail to grasp the scope of the problem; the eugenics movement actually began in America. California adopted eugenics laws in 1909 and ultimately sterilized 60,000 people who did not have the desired Nordic traits. Gas chambers were created to exterminate individuals who were considered faulty. Even Supreme Court justice Oliver Wendell Holmes declared that “three generations of imbeciles is enough.” Fortunately, the eugenics movement lost popularity after it became associated with the Nazis, but it goes to show that artificial selection can have cruel and deadly consequences. For every trait that we select, hundreds of thousands of individuals without the trait are condemned to death. We must be careful that we don’t take selective breeding too far, or else we could end up as cruel, inhumane murderers.

    Sources: Wikipedia
    http://www.waragainsttheweak.com/offSiteArchive/www.sfgate.com/index.html
    http://archaeology.about.com/od/domestications/qt/dogs.htm

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  3. Well we classify species as those that can reproduce with one another. Like Coyne talks about how we are one species, even though there are many variations, but we have to be careful with this subject because it touches the issue of race. They experience so much variation because breeders want to create those adaptation are the most favorable. Though our generation is focused not just on favorable, but if you were to create adaptation of a specie that was very rare, then you would be able to get a lot of cash. We want dogs that are able to do good things also like the dogs that aid people. You will need to be able to get a dog that is calm, and not excited all the time, and one that is intelligent to be trusted to help a person.
    Artificial selection would be evidence for natural selection because it shows how traits evolve generation to generation. I agree with Annie in which she saids that people are able to speed up the process of natural selection. We basically eliminate the poor genes of one species and only put in creatures with good genes. What would take evolution and natural selection to work a while, we eliminate those bad variables. So by speeding up the process, we have animals that we like and want basically, and we ruin the natural processes of natural selection.
    An animal that has been bred for a desirable variant would be greyhounds, and horses. Since I have greyhounds, I can see why these animals are bred. They are very quick and if you breed one that is very fast, you will be able to make a lot. Horses are the same way, they are used for races.
    Though we can see that through these adaptations, we are using these animals to our benefit, and now be are judging it as cruelty. So in my opinion this artificial selection is wrong, but only pertaining to animals because we only use them to our benefit to make money. The only way i would let this slide if it was helpful to someone like the guide dog. We should let natural selection run its course and let life be life. Let's not try and change things from what they should be.

    Sources:


    Annies comment

    http://en.wikipedia.org/wiki/Species

    http://en.wikipedia.org/wiki/Artificial_selection

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  4. First off, it is important to define what a species is. Coyne describes a species as being “reproductively isolated from one another” (172) and the “unit of evolution” into which members of a species evolve, sharing genes, appearance, and behavior (174). By this definition, different breeds of dogs may still be considered one species; their major differences come from variations in size, fur, and disposition (tailored to their purpose – whether they are more suitable for hunting, companionship, etc). The mechanism for this human-driven breeding for what we deem desirable in our domestic dogs is called artificial selection. Artificial selection is suggested by Coyne to be good evidence for natural selection because it is a good parallel that acts in a time appreciable for humans to comprehend that changes do take place and that given evolutionary time, it is quite possible and even likely that evolution is taking place and is very real. As Coyne outlines on page 126, the breeding of dogs mirrors natural selection as a mechanism for evolution, and satisfies all the tenets of evolution except speciation. Artificial selection means that instead of natural forces working to select the most reproductively viable and the “better” genes, humans choose which dogs get to survive to reproduce based on what they feel is aesthetically pleasing to them. That is to say, the criteria for selection is that random mutations must create traits that are enjoyed by humans, since they will reproduce. The argument is that it is simply just a different stimuli, a different force for natural selection (one that isn't so natural, but rather based in whim).

    One of the responses above says that 'for every trait we select, hundreds of thousands of individuals without the trait are condemned to death'. This statement is very weighty, but given the context, can be misleading. In artificial selection, (just like natural selection), one particular trait, associated with a particular gene mutation, is preferred over another, and allowed to reproduce with greater success than the individuals that do not have the trait. These individuals lacking this trait aren't necessarily condemned to death per se, but rather are just less likely to reproduce given the mechanism for evolution under which we all work. Also, going off the last response given above, there is a mention of poor and good genes. Natural selection will “promote” the genes that are more favorable for the individual's fitness and the individual's reproductive fitness at the time. Thus, poor and good are irrelevant and relative. And when taking artificial selection into account, one may argue that what humans necessarily select for aesthetics may not be the “good” genes for the animal. (I would disagree with this, because given the definition of evolution by natural selection, since humans provide for the animals to reproduce successfully, dogs with aesthetically pleasing traits to humans will increase their reproductive fitness and survive longer as well because they will be more likely to be appreciated by humans.)

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  5. …(cont'd)
    One, final thing I have to note about right and wrong in terms of artificial selection is that, though I do believe it is wrong, by my own moral standards, I think it has no worth in a discussion of evolution. Morals are not taken into consideration in natural selection driven evolution, and though we are imposing our own will when breeding dogs or producing seedless watermelons, they are another stimuli for which the species will undergo changes, the most suitable of which will be passed onto the next generation. In the example of the svelte turkey, consider this: the new born turkeys that can't stand due to their enlarged breasts don't have any idea of what it might have been like to be able to move if humans had not interfered, and (though this is disputed) they do not seem to show the capacity for outrage for having their human “natural rights” imposed upon. These moral standards are inherently human, and since humans are another species interacting in the world, whatever they do with their superior intelligence (at least, to us) to change the world is a fair stimulus around which other species may undergo changes and therefore evolution over time. How is it any different than developing adaptations to defend against new predators?

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