On page 139, Jerry Coyne states that laboratories can make certain specimen undergo "genuine evolutionary change" because it provides all three requirements of evolution: variation,
heritability, and the differential survival and reproduction of variants. Jerry Coyne argues that this is better than artificial selection; what is your opinion on the idea these laboratory experiments demonstrate evolutionary change? If so, is it possible for humans to elicit certain mutations to occur in certain specimens; thereby, controlling evolution of these specimen? If not, what are the limits or errors that prevent these experiments from eliciting "genuine evolutionary change"? Give examples and an explanation stating your argument.
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An example of test tube change is found on pg. 128 (in Coyne’s book), in experiment done by Lenski at Michigan State University. Identical E. coli strains were grown where the E. coli had access to sugar glucose food at the beginning of everyday but this supply was depleted by the end of the day. As you may remember from the glowing bacteria lab (near Halloween), E. coli is a great example species to use for laboratory tests because E. coli are not highly toxic and the time between generations is on average only 20 minutes (biology-online.org). The experimenters were testing the effect of this type of feast-and-famine environment on the ability of E. coli to adapt. Since this is a well designed experiment, it displays the theme of science as a process. The researchers asked a question and continue to pursue this question through experimentation. The experiment yielded results that show significant evidence of evolution. 18 years after this experiment began, the bacteria that have been living in the feast-and-famine environment can grow 70% faster under these conditions that the original strain that did not undergo selection. Furthermore the scientists identified nine specific genes that mutated to cause the adaptation to the feast-and-fast environment. There is no doubt that genuine evolution occurred. The population in the feast-and-fast environment is clearly genetically different that the original strain, showing change over time to better suit a specific environment.
ReplyDeleteLike Sami posted, the evolution in these experiments is absolutely genuine. These bacteria have the requirements necessary for genuine evolution; variation, heritability, and differential survival and reproduction of variants. I’ll focus on a different experiment than the one at Michigan State University. Barry Hall’s experiments at the University of Rochester are important in showing how test tube evolution is genuine. In this experiment, Hall removed a gene from E. coli that produced an enzyme that is crucial in the process of breaking down lactose into smaller units. When put into an environment of only lactose, the bacteria obviously didn’t grow, because the enzyme necessary for the bacteria to “eat” was missing. However, Hall quickly found that as time went on, the E. coli were able to “eat” the lactose because of mutations in the genes that allowed a new enzyme to be produced that would help the bacteria take up food. This experiment conclusively shows that evolution occurred because an organism adapted to its surroundings to enhance its chances of survival(Coyne 129). As Sami said, this experiment touches on the theme of science as a process. Scientists conducted an experiment, and in the process were able to make many conclusions and learn important lessons. This is without doubt genuine evolution; E. coli was genetically modified through natural selection in the same way that millions of other organisms are. This experiment relates to our study of lactose intolerance and the lac operon. In lactose intolerance humans, people lack lactase, which is necessary in breaking down lactose to smaller subunits like glucose and galactose. http://digestive.niddk.nih.gov/ddiseases/pubs/lactoseintolerance/. This is exactly the same situation as the originally modified E. coli were in. Because bacteria reproduce so quickly(up to once every 20 minutes), natural selection and genetic mutation occur much quicker than in humans. As a result, the experimenters that E. coli was able to adapt quickly. Hopefully, when as time goes on and more genetic mutations in humans occur, the same thing will happen and new genes will create new enzymes which will then be able to break down lactose.
ReplyDeleteKevin and Sami both bring up good examples backing up the legitimacy of test-tube evolution. Another example can be seen on pages 129-130, when Coyne discusses the research of Paul Rainey and his colleagues at Oxford. Rainey put a strain of the bacteria Pseudomonas fluorescens in a vessel with nutrient broth. The vessel contained different environments within it, due to differences in oxygen concentration at the top and bottom. After ten days or a few hundred generations, “the ancestral free-floating smooth bacterium had evolved into two additional forms occupying different parts of the beaker.” (130) Further testing proved that the two new forms were different genetically from the ancestor. The first thing to note here is that natural selection for the fittest genotypes for each environment was the means for the evolution of Pseudomonas; even though it was only in a vessel, genuine evolution occurred. Not only that, but speciation happened in the lab right before Rainey’s eyes as Pseudomonas adapted to each environment inside the vessel.
ReplyDeleteLike both Kevin and Sami point out, test tube evolution relates to science as a process, since for example, Rainey and his team started out with a question, created experiments to try to get an answer and used the evidence gained to address bigger thoughts and ideas about evolution.
Source: http://evolution.massey.ac.nz/rainey/