Argue which one of the eight themes is the most reoccurring theme in the book, not including evolution. Be sure to be able to define what the theme means as well as refute why another theme that appears in the book should not be considered as the most reoccurring theme.
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ReplyDeleteJ. Cohen, I think continuity and change is definitely seen in evolution. However, I think that relationship between structure and function is a more reoccuring theme. Evolution results in the survival and reproduction of the genes of organisms that are most able to survive in the world. In order to survive and reproduce, an organism's structure must fit the organism's function.
ReplyDeleteSquid are predators that have the structure (the siphon and tentacles) to quickly move by jet propulsion and capture prey. Additionally, since squid are also prey, squid have the ink sac, a structure whose function is to prevent predators from eating squid. These structures have evolved because of the squid's niche in the squid's environment, the squid's functions of eating and escaping prey.
At the same time, Coyne uses some instances of bad structure (design) to support evolution. One of his primary examples is the laryngeal nerve in humans. The laryngeal nerve's function is to allow humans to speak and swallow. The laryngeal nerve obviously possesses an important function. Despite this, the nerve has evolved from our ancestors, the fish. Because of evolution, the laryngeal nerve runs down into our chest and loops around the aorta instead of following a direct path from the brain to the larynx. The structure of the laryngeal nerve increases the risk of injury to the nerve, which would impair the ability to speak and swallow. This instance of structure seeming to reduce the optimal ability to function is an example of evolution that also shows the theme of the relationship between structure in function.
Therefore, rather than continuity and change, I believe the most reoccurring theme seen in evolution (other than evolution itself) is the relationship between structure and function. This relationship is seen in both good designs and bad designs, both resulting from evolution.
I would say that the (second) most recurring theme in "Why Evolution is True" would be “continuity and change,” or the similarity of traits due to DNA sequences that are passed down over the generations, as well as the mutations that cause changes in these traits (Campbell 8). The process of evolution relies on this theme; the evolution of a species is marked by differences in traits that “are based on changes in DNA, which originate as mutations” (Coyne 3).
ReplyDeleteOn page 29, Coyne mentions that "the most recent fossils are those most similar to living species." This demonstrates continuity, since the evolution of traits is gradual. We would recognize more traits in the fossils of chronologically closer species than in those that are further apart. For example, mammals share more traits with reptiles, which appeared approximately 50 million years apart (Coyne 27) than with lobe-finned fish, which appeared 150 million years apart (Coyne 28). The phylogenic tree from the vertebrate unit also shows how traits evolved sequentially (Campbell 699). For example, all craniates are chordates and have a head, while all vertebrates, in addition to being craniates, also have a vertebral column.
In addition, the evolution of traits is a direct result of changes in DNA. In the transformation lab, the addition of the pGLO plasmid, with the gene bla that coded for resistance to ampicillin, gave the E. coli the ability to survive in the presence of the antibiotic ampicillin. As a result, the E. coli that survived passed on the gene for ampicillin resistance to its descendants, resulting in several colonies of antibiotic-resistant bacteria. Coyne references this on page 130, revealing that introduction of penicillin in the 1940s was able to wipe out most strains of S. aureus: however, the only strains to survive were ones with mutations that made them resistant to penicillin. As a result, most of the staph strains today are resistant to penicillin because they are descendants of the mutated strains from the 40s.
Although other themes also appear in Coyne's book, they are not as reoccurring as “continuity and change.”
"Energy transfer,” the exchange of matter and energy between organisms in an environment (Campbell 6) does play a role in determining which traits get passed on. Traits that are too energetically expensive (such as ornaments in chapter 6, “how sex drives evolution”) do not provide a selective advantage. However, energy transfer does not explain how traits develop in the first place.
Regulation and feedback mechanisms don’t really apply to evolution, since there is no “end product” that affects the process of “production.” (Campbell 11).
Interdependence in nature, the reliance of an organism on biotic and abiotic factors in its environment, is like structure and function in that it explains how traits evolve by providing a selective advantage in a certain environment (like the sand-colored mice that depended on the color of the background for camouflage). However, interdependence in nature doesn’t take into account how evolution can occur without selection due to genetic drift (Coyne 123).
Dennis H., I would agree that the relationship between structure and function demonstrates how traits seem to match their environmental challenges; however, I would say that the theme of continuity and change, as the genetic engine behind the development of all traits, is more present throughout the book. Continuity and change explains how, on a molecular level, all traits are able to exist, through mutations and inheritance of genes.