Wednesday, March 31, 2010
Artificial Selection v Natural Selection
In chapter 5, "The Engine of Evolution," Coyne brings up animal and plant breeding as a means for people to see the process of natural selection leading to evolution happen in their lifetimes. Why is artificial selection a good parallel to natural selection? Coyne uses the example of dog breeding and the rapid creation of new species as a way to see and understand evolution by selection, saying that "the success of dog breeding validates two of the three requirements for evolution by selection." Which requirements is he referring to and how does dog breeding validate these requirements? Provide another example of artificial selection he discusses that does the same.
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The three requirements of evolution referred to are variation, heritability and the differential survival and reproduction of variants (Coyne 128). The requirement missing in reference to dog breeding is the differential survival and reproduction of variants. Since humans are specifically choosing which dogs can reproduce and with which other dog, there is no true differential reproduction of variants. Variation and heritability are present in dog breeding, as seen in the hundreds of breed all belonging to the single species Canis lupus familiaris (should be italicized).
ReplyDeleteAnother example of selective breeding, which also exhibits the two requirements of evolution, is the evolution of tomato plants. Selective breeding of plants began when early humans who planted tomatoes would replant the mutant tomato seeds which yielded the largest tomatoes. Large tomatoes thus had a selective advantage because it (the larger tomato) was more likely to be planted by humans. Thus, humans facilitated the evolution of tomatoes into the large two pound variety we can purchase today (Coyne 127).This type of selective breeding, in addition to exemplifying the theme of evolution, also shows the relationship between structure and function. The larger structure of some tomatoes, suits the function of being more attractive for humans to replant.
The key factor in differentiating natural and artificial selection is whether or not the species is evolving to better suit the environment (natural) or specifically changing to suit the needs of humans (artificial). The forces of nature, whether it be harsh weather or a predator, cause the death or lack of reproduction of the fittest in natural selection. In artificial selection, humans do not allow undesirable organisms to breed at all. Not all adaptations that arise from selective breeding are selective advantages for living in the wild. A dog that is breeded to be docile and small would not fare well in the (wild) natural environment. Likewise, a flower with certain color petals or aromas may be pleasing to humans but not attract bees in a natural setting (and thus would not be pollinated and would not reproduce).
An important part of artificial selection versus natural selection is the relative rate at which both occur. Going along with the dog example that both Radhe and Sam mentioned, Coyne comments on the relative rates of each. Coyne writes, "What is most astonishing about dog breeding is how fast it got results." He also states that it took "only 0.1 percent of the time that it took wild dog species to diversify" (Coyne 126). 0.1 percent means that artificial selection occurs 1000 times faster than natural selection. Looking at this incredibly fast rate, it is quite easy to see that species that evolve from artificial selection gain an advantage from those that evolve over the course of natural selection. Artificial selection also allows for a specific type of evolution that someone wants. For example, a dog breeder can cross breed two specific types of dogs to create a whole new breed.
ReplyDeleteCoyne mentions numerous different types of vegetables that have undergone artificial selection, but I thought his most interesting example was when he discussed turkeys. Particularly, when Coyne writes "Through selection, the svelte wild turkey has become our ... Thanksgiving monster, with breasts so large that male domestic turkeys can no longer mount females, who must instead be artificially inseminated" (Coyne 127). This quote reminds me of a show I was watching just this weekend about the mass production of turkeys. Turkeys are hatched in a hatchery, and then taken to a large warehouse type space. From here on out, the turkeys are never see the light of day. Every part of the turkeys' lives are monitored, from the type of woodchips used on the ground, to the feed used, to the temperature in the warehouse, to the amount of lighting used to simulate the mating season year-round. It is amazing how careful and meticulous the whole process must be, but it also a testament to the artificial selection that produced the turkeys that everybody loves to eat for Thanksgiving. The turkeys have evolved to thrive in their artificial environments, and grow as quickly as possible.