On page 131, Coyne cites resistance to penicillin as a prime example of natural selection. Penicillin was once very useful in curing infections caused by the bacterium Staphylococcus aureus; however, now, the effectiveness of penicillin has decreased significantly. Briefly explain how this demonstrates natural selection. Also, please relate to a biological theme. Furthermore, some food for thought: could this resistance actually come from the habituation of patients to penicillin as opposed to evolutionary adaptations of the bacterium itself - why or why not?
On pages 131-132, Coyne goes on to consider certain strains of bacteria/viruses that have not evolved resistance to vaccines/antibiotics. What causes certain strains to adapt and others to fail at adapting?
Finally, Coyne states that "when a population that encounters a stress that doesn't come from humans..., natural selection will often produce an adaptive response" (132). Evaluate the truth behind this statement. For instance, can you cite any other examples (besides Staphylococcus) where organisms have formulated an adaptive response to human-induced stress? Or, if you prefer, can you cite any organisms that have adaptive responses to nature-induced stress (salinity, pH...etc)? Be sure to consult Campbell and other sources for your answer.
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Bacteria that are able to resist natural selection is an example of natural selection because it demonstrates how one gene facilitates a species’ survival, and that gene is passed down to future bacterium generations. This population that has the gene for penicillin survival will grow, yet those that don’t have the gene will still die. Therefore, because of genetic variety, the bacteria will survive.
ReplyDeleteThough I don’t know much about the human immune system (since we haven’t studied that unit yet), I would guess that there is a chance that drugs might stop fighting off pathogens because of human habituation. A person’s genetic code may cause white blood cells to engulf Penicillium, causing bacteria to take over the body. It all depends on whether someone’s genetic code causes the immune system to fight off some antibiotics.
The strains of bacteria that are able to adapt to a drug do so after multiple generations because mutations finally occur in the bacteria’s genome that helps it survive. We have learned in class that some bacteria even acquire genes for resistance by transformation. Transformation is “the change in genotype and phenotype due to the assimilation of external DNA by a cell” (306). These bacteria that acquire DNA via transformation are also able to survive. However, the bacteria that aren’t able to survive simply die out, while those with the resistance gene pass it on to further generations.
I really don’t think that Coyne’s statement about “adaptive response” is entirely true. Though there is a chance that bacteria develop resistance to antibiotics, natural selection doesn’t produce “an adaptive response.” Evolution has no direction, as Coyne even implies by saying “species don’t try to adapt to their environment. There is no will involved, no conscious striving” (117). The “use and disuse theory,” what adapting to a human-induced stress implies, is Lamarck’s theory of evolution, a theory that was prior to Darwin’s (Campbell 454). Darwin disproved Lamarck’s theory in his first chapter of evolution, and it is the theory that many, if not all, scientists accept today.
However, what Coyne does explain right is that genes “that produce better adaptations become more frequent over time” (117). This statement is explained by natural selection. Going back to the penicillin example, if a population of bacterium is seen with the penicillin resistance gene, then future generations will have this gene in their genomes too because the ones that actually survive are the ones with this gene. This is a good example of the theme continuity and change. Even though the population of the bacterium is continuous, the population is also changing because natural selection only allows those with penicillin resistant genes to survive. These genes are passed on, and the population continues to live while it is still ever changing.
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ReplyDeleteStaphylococcus's adaptation to penicillin is evidence of natural selection in that drug-resistant bacteria have a selective advantage to non-resistant bacteria after penicillin is introduced into the environment. Because of this selective advantage, drug-resistant bacteria are more likely to survive and reproduce, and therefore would eventually become the dominant population of Staphylococcus.
ReplyDeleteSome bacteria are unable to evolve drug resistance simply because the genetic mutation never occurs. However, if the mutation does occur, it can spread within the bacteria population very quickly, for not only does the mutation spread through bacterium's incredibly high reproductive rate, but also can be transferred betweeen individual bacterium to conjugation and recombination (Campbell 563).
Another example of an organism that has adapted to human-induced stress is the raccoon. Much of the natural habitat of the raccoon was destroyed by human land development. Instead of migrating to pockets of natural habitat or dying, the raccoon adapted to the human-induced change. The raccoon has become a mesocarnivore, and takes advantage of artificial food sources common in developed areas in the form of trash dumps and parks. This adaptation is a selective advantage because it allows the raccoon to exploit a food source that is inaccessible to many organisms and therefore decreases the likeliness of premature death due to starvation. This also relates to energy transfer in that the raccoons are taking advantage of the potential energy found in the trash of humans and use the energy to perform biological processes such as reproduction. Indeed, the raccoon has so successfully adapted to developed areas that it is considered a common pest in many cities. (https://fp.auburn.edu/sfws/ditchkoff/PDF%20publications/2006%20-%20UrbanEco.pdf)