As we conclude this most amazing blog, I feel we should concentrate more on big-picture ideas and themes that Carroll has emphasized throughout his book, one of which is the genetic perspective on evolution.
Why is DNA, both new and old, critical to the explanation and support of evolution? In what way is a genetic perspective effective? Also, describe TWO examples in which Carroll uses DNA evidence to bolster support for evolution. (myriad examples of this are furnished in the book...)
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DNA is critical to the explanation and support of evolution because it is the genetic code, the code that makes up each organism. It is the unique sequences of nucleotides, those bases, sugars, phosphate groups - that make up an organism. The variety in the sequences is the cause of the evolutionary time-frame. With mutations continually bombarding the genetic code, nucleotides are changed, frame-shift and point mutations occur - as well as other types of mutations. All of these mutations cause a different function to be used by the organism: some mutations might create a new function such as the creation of opsins over long periods of time; others might create a loss of function - namely, the loss of sight. DNA's universal use among all species makes it so wondrous. DNA is critical to the explanation and support of evolution because it is the cause of evolution in a sense. As stated above, mutations in DNA cause different functions to be gained or lost. With these gain and losses, natural selection allows those functions that are favorable in a certain environment at a certain time to thrive. Those functions of organisms that thrive eventually become adaptations. A genetic perspective is effective because it is the source of evolutionary adaptations. It is the source of how the organism came to being (i.e. using fossil genes, LINES, SINES, etc). It is the source of all mutations that could possibly occur in the future.
ReplyDeleteOne example that Carroll uses in the novel is about the icefish, which is referenced throughout his novel. "The clear, stunning answer to the question of what happened to their hemoglobin came from the study of icefish DNA more than forty years after Ruud first sampled their blood. In these amazing fish, the two genes that normally contain the DNA code for the globin part of the hemoglobin molecule have gone extinct. One gene is a molecular fossil, a mere remnant of a globin gene - it still resides in the DNA of the icefish, but it is utterly useless and eroding away, just as fossil withers upon exposure to the elements. The second globin gene...has eroded away completely. This is absolute proof that the icefish have abandoned, forever, the genes for the making of a molecule that nurtured the lives of their ancestors for over 500 million years," (Carroll 23). This example is Carroll's first use to explain how DNA links to evolution - the favorable adaptation allowed the icefish to thrive in the cold waters.
Another example where Carroll uses DNA evidence to bolster support for evolution is his description of the MC1R gene, "From what we know already, it is clear that there must be at least ten different ways to mutate MC1R to darken fur, plumage, or scales. With ten target sites in the gene, and the same mutation rate...what are the probabilities that an MC1R-caused black variant will arise? It is 10 times higher than the probability of the exact change in the SWS opsin. Therefore, 1 in about 75 million offspring will be black," (Carroll 158). Carroll makes a point of stating that evolution happens over years and years of time and not instantly. The MC1R gene, part of the genetic code, is one that can be mutated and is linked to the biological theme of evolution.
Even so I could never hope to forge a blog posting as eloquent as Daniel's, I will do my best to add 2 cents. I believe the DNA point of view was taken because in all realistic honesty, it is the only perspective that can hope to prove the reality of evolution. One example are the SINES and LINES (as shiekh has noted, which are basically genetical markers letting us know that two species are related to each other in some way, and thus in a sense, "one evolved from the other".
ReplyDeleteAnother key aspect to DNA is that is is an ever growing library among species, and as Carrol has noted "new traits are constantly evolving". I believe our long forgotten single cell ancestors never imagined the ability to see, hear, feel, touch, and think really. DNA is like a cooking recipe, and the more mutations and odd recipes come into effect, the greater the probability of new and interesting things coming to life. I mean several of the animals on our planet are so spectacular and odd, and the key to their diversity lies in their genetic code. Just today I heard of an "Immortal" jellyfish that can revert to its polyp form if stimulated... I mean wow! And the only way to truly inspect the cause root of such phenonmen's is inspecting a creatures DNA. A fossily could say some things, but the DNA is truly the bluprint of life as we know it.
Danyal and Boris effectively address most of the reasons why the genetic perspective is very effective. In addition to the previously stated reasons for why DNA is integral to proving evolution, as Carroll himself points out, incorporating DNA into the evolution debate provides further evidence supporting evolution and can be used to debunk many intelligent design theories. Also DNA serves as a perfect library, as Boris says, of mutations a species experiences. Due to the universality of DNA, scientists can compare the genomes of two closely related organisms and their common ancestors to track down specific mutations that led to speciation. Similar studies can allow us to track the evolution of individual traits themselves and address the issues surrounding the development of complex structures related to the studied trait.
ReplyDeleteCarroll uses DNA to explain how complexity and variation in structure could arise in nature by discussing the Pax-6 (italics for entire post) gene. Addressing a widely disputed issue, Pax-6 is part of the genome of every organism with eyes. Pax-6 shows us that variation in complex--sometimes irreducibly-- structures can arise in nature through Darwinian evolution because groups of organisms share a genetic “toolkit” for organ building.
Carroll also shows us how variation can occur in very closely related organisms. He gives us the example of the pelvis reduced and full pelvis stickleback fishes that are so closely related that they can reproduce and produce offspring. The two forms of stickleback also share the exact same toolkit gene: Pitx1 (italics for entire post). However, gene theory resolves this issue by showing us that the Pitx1 gene is inactive in the pelvis reduced stickleback because the regulatory DNA sequences related to Pitx1 are altered in the pelvis reduced.