Thursday, April 15, 2010
Dogs
On page 125 Coyne talks about the breeding that humans have done of the domestic dog in relation to evolution by selection. The dogs all come from ancestors of other animals that were not forced to live in captivity and when they were evolved into the dogs that we know today. These include around 150 breeds of dogs that were created due to human action. "Breeders have virtually sculpted these dogs to their liking..." (126). Was this human influence on dog evolution harmful to the ancestors that they came from? Should the breeding of dogs for things like the shade and thickness of their coats be allowed even though it may cause health problems and interferes with natural selection? Discuss the effect that this evolution by selection has on the process of natural selection and give other examples of evolution by selection. How do wild dog breeds and domestic dog breeds differ and relate to each other? Contrast and compare artificial selection versus natural selection.
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Well, the ancestors of dogs are currently extinct so we can't really say if our breeding is harmful to the ancestors.
ReplyDeleteDog breeders isolate a certain trait that they like about a certain dog and breed with it, hoping that that trait would continue to be passed on. This is has happened for a very long period of time, and of course isn't limited to just dogs. We regularly breed cows and other livestock animals, along with plants, and select the traits we like and reproduce them.
Technology has come to the point where natural selection no longer is a dominating force acting upon a dogs life. We have veterinarians who can provide treatment to sick dogs, dogs that would have normally died if no such treatment was provided. Breeding also does not necessarily produce a negative effect on the dog. Of course a dog dying because humans don't want its genetics is detrimental to that dog, but I'd say overall breeding has proved beneficial for the dog species. Just like in humans where there is a higher probability of disease from reproduction of the same family, a similar trend can be attributed to pure bred dogs. Crossbreeding arguably provides a healthier result. Furthermore, the plentiful food supplies created by humans reduces the need for hunting, unless you are a hunting dog.
A wild dog is by no means stronger than a domesticated dog. A study I saw once on Discovery Channel showed that a domesticated guard dog had much more jaw power than the strongest wild dog they could find. For other animals, a supercow is currently being bred, which yields much leaner and tender meat than regular cows. Geneticists continue to breed this cow by isolating healthy sperm and healthy egg cells from the strongest cows they bred to continue this evolution of the supercow (you can find this on youtube). In general, artificial selection by humans tends to create a stronger result for the task we want that animal to do; although, not necessarily for that animal to just simply survive and reproduce.
Sources:
http://www.k9web.com/dog-faqs/breeding.html#potential_hereditary_problems
http://en.wikipedia.org/wiki/Dog_breeding
http://www.1902encyclopedia.com/D/DOG/dog-01.html
http://www.youtube.com/watch?v=Nmkj5gq1cQU
Humans most likely didnt have a harmful affect on the ancestors of dogs. This was most likely the Eurasian Gray wolf, and humans began to breed them to their own needs. This probably didn't cause harm to the species, it just took it from its natural path of evolution on to a man-made one. Humans interfered with natural selection long ago (starting about 10,000 years ago) so it is too late now to worry about the interference of humans and evolution. Also, the breeding humans do, for the most part, does not result in health problems. They live healthily until atleast the age of reproduction so that they can have offspring and pass on their genes. This would not be eliminated by natural selection, since they are able to reproduce, so the artificial selection is not harming the species. For this reason, there are no laws against breeding dogs, because there is no harm being done to them. There are a lot of differences between wild dog breeds and domestic dog breeds. The amount of diversity between wild dog breeds is much smaller than the diversity seen in domestic dog breeds. Domestic dogs range from 2 pounds to 180 pounds while wild dogs range from 2 to 60 pounds. Also the diversity in wild dogs arose through natural selection and took over one thousand times longer than the diversity created by artificial selection in domestic dogs.
ReplyDeleteThere are numerous examples of species that have been artificially selected through humans. Agriculture is a major reason for artificial selection. Humans want the most quantity and quality food. Humans have selected corn, tomatoes, cabbage, and many more crop plants. Many of these, like corn, are easily recognized today, but "you wouldn't recognize the ancestor of our ear of corn, which was an inconspicuous grass" (127). They have come a long way because of humans and artificial selection.
Artificial selection is much quicker than natural selection. Both have variations produced by genetic mutations, but they may not always be chosen in natural selection, and in artificial selection the breeder decides. Also, artificial selection doesn't always necessarilly result in the strongest and most able to survive and reproduce, while natural selection only chooses the mutations most fit for surviving and reproducing.
Sources:
Why Evolution Is True
http://www.learner.org/courses/essential/life/session5/closer1.html
http://library.thinkquest.org/C0118084/Gene/Genetic_variation/artificialselection.htm
Dog evolution wasn’t a harmful process, as I’d expect the wolf that now weighs from 45 to 120 lbs or even its ancestors wouldn’t have exactly went along with the process. Wolves are wild creatures and the reason they were easy to tame is because we took advantage of their basic needs. These basic needs are food, shelter, and care. We still see wolves scavenging campsites when campers leave food left out in the open. Wolves, like any animal, need to eat, so it would make sense by offering them food that we’d form a bond. I’m sure at first it wasn’t a very strong one. Maybe wolves only followed humans to get the scraps of the meals they left behind. After all, we all know how wild animals are skittish around humans and need to maintain a certain distance before feeling threatened. This distance, called the “flight distance”, might have decreased as time went on until humans were actually able to touch wolves. Of course, this happened over generations. It wasn’t like the wolf was domesticated overnight. Another way wolves were domesticated were by taking in orphaned wolf cubs and raising them alongside our own children. According to Wikipedia, this is how the evolution of dog like behavior formed over time. What proof do we have though that these methods even helped domestication? It sounds good in theory, but is there is a way to prove it? An experiment was conducted just to figure that out called the “farm fox” experiment. These researchers selectively bred silver foxes in attempt to domesticate them. After thirty-five generations and forty years, these foxes appeared more dog-like, becoming friendly, having curled tails, and having floppy ears (Origin). They were as tame as dogs and even developed new coat colors. Obviously, domestication of these foxes was successful and it illustrated that domesticating wolves had only taken time and patience.
ReplyDeleteSelective breeding wasn’t started with the idea of keeping dogs healthy unfortunately. As Coyne said, it was to have, “the elongated, short legged dachshund, ideal for catching badgers in their holes; retrievers, bred to fetch game from the water; and the fluffy Pomeranians, bred as comforting lap dogs” (126). Even more, border collies are made to herd sheep and German Shepherds were selected to protect flocks from predators. These dogs have a purpose, and though a healthy dog is important, issues in each breed was more of a side effect when they were being selectively bred. An example I’ll use is with the German Shepherd. These big dogs are used as both house pets and workings dogs, being beautiful canines and very sociable. Unfortunately, their breed has an issue with hip and elbow dysplasia. There has been effort to reduce disease in the breed, but even now they’re being used less in the police force (Wikipedia). Like Potpie addressed, crossbreeding is a way to breed healthier dogs while purebreds that are normally over bred have more health issues.
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Another example of an animal that has been domesticated and selectively bred is the turkey. As Coyne addressed in his book, domestic turkeys are huge meaty birds and “with breasts so large the male domestic turkey can no longer mount females, who must be instead artificially inseminated” (127). Though the bird is highly dependent on humans, it was selected by us in order to get the most amount of meat out of the turkey instead of being a successful independent organism. Others, brought up by Corey, are corn and other vegetables. Selective breeding associated with food is normally to increase the amount/size and to manipulate with the taste of the crop. Diving right into the artificial selection vs. natural selection, this is just an example of how artificial selection gives the breeder the ability to decide which traits they want to see past down to the next generation. According to Coyne when it comes to artificial selection, “the criterion of reproductive success is human desire, rather than adaptation to natural environment” (127). Natural selection wouldn’t have allowed the domestic turkey to become incapable of reproducing on its own. It’s currently situation is all because of artificial selection.
ReplyDeleteWild dogs and domesticated dogs relate in several ways. Wilds dogs like wolves or African wild dogs are very social pack animals as domesticate dogs are very social with humans. Some even say domesticated dogs look at their families like their packs, with their owners being the Alpha. Wolves and quite a few species such as the Mackenzie River dog and Eskimo dog resemble each other greatly with appearance and vocals (Dog). Also wolves and dogs show a lot of the same time of body language behavior. When afraid they tuck their tails under their legs and when they are frightened they bare their teeth and growl. Dogs also are like wolf puppies because they as well show those tail wagging and whimpering characteristics (Wikipedia). When it comes to contrasts in wild canines and domesticated ones, wild dogs do not bark. As puppies they might yip or be more vocal, but adult wild dogs are a lot more silent. Also wild dogs don’t have such a spectrum of breeds as domesticated dogs have a total of 150 breeds that are recognized. Also they are all around the same shape and size while domesticated dogs can be as tiny as a Chihuahua or as big as a Newfoundland.
Sources:
Why Evolution Is True
http://www.1902encyclopedia.com/D/DOG/dog-01.html
http://en.wikipedia.org/wiki/German_shepherd
http://www.articlesbase.com/pets-articles/origin-of-the-domestic-dog-130582.html
http://www.everythingwolf.com/facts.aspx
http://en.wikipedia.org/wiki/Origin_of_the_domestic_dog
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