The Argument-
David Shenk states that "[Epigenetic change] offers not just another mechanism by which species can adapt to changing environments, but also the prospect of an evolutionary process that is more interactive, less random, and runs along several different parallel tracks at the same time" (161). How will this finding affect the current definition of evolution? What effect does community ecology have on evolution? Due to the importance of environmental factors, do entire communities evolve together, adapting to gain the advantage over one another? Furthermore, how does this affect the role of randomness in evolution? What role do mutations play in changing the phenotype of an organism? And what kind of epigenetic factors can parents pass down to their offspring to impact evolution? How do epigenetic changes and mutations work together to affect gene expression? Focus on the biological theme of evolution. Refer to chapter 54 for community ecology, chapter 14 and 15 for inheritance, chapter 17 for mutations, and chapter 18 for gene expression and epigenetic inheritance. Examine how all these factors work together to drive evolution.
Aaron Zalewski (bitquest@yahoo.com)
While learning that gene expression and heredity can be affected by epigenetics, the definition of natural selection and evolution should be updated since epigenetics complicate current concepts. According to David Shenk, the current understanding of evolution proposed by Darwin—that evolution happens when “genes are altered…by random mutations”—is too simple (p. 156). “Randomness” means very little now because the idea of epigenetics reduces the “randomness” of the evolutionary process. Epigenetics introduces the concept of “free-will” (p. 160). If a person’s lifestyle or environment can influence their genome, then humans do have control on their gene expression and heredity at least to some extent.
ReplyDeleteIn ecology, epigenetics is a rather new field and is often misunderstood. David Shenk explains, “epigenome can be altered by the environment and is therefore an important mechanism for gene-environment interaction” (p. 159), which shows that community ecology has a large influence on evolution since it is full of interspecific interactions between species and its habitats. Epigenetics can be a source of heritable phenotypic variations independent of DNA sequence variation (http://www.researchgate.net/conference/ESF-EMBO_Symposium_Epigenetics_in_Context_From_Ecology_to_Evolution/). Epigenetics could have a role in shaping the results of interactions—competitive exclusion, for example.
The term, “competitive exclusion”, was coined by Russian ecologist G.F. Gause to explain how two species competing for the same limiting resources cannot coexist in the same place. Eventually, the inferior competitor will become extinct, while the superior continues to use the resources more efficiently. For example, Paramecium caudatum was driven to extinction by Paramecium aurelia when cultured together, in which Gause concluded that P. Aurelia’s competitive nature allowed it to survive and reproduce more than P. caudatum (Campbell 1199). Rather than simply attributing it to random mutations as Darwin would, epigenetics can narrow it down to specific changes in the epigenome by either DNA acetylation or DNA methylation.
Tracy Lai(tracymlai@hotmail.com)
DNA acetylation refers to attachment of acetyl groups to lysines in histone tails; this attachment loosens histone tails and gives transcription proteins more access to genes. DNA methylation is the complete opposite: the addition of methyl groups promotes condensing of the histone tails, inhibiting gene expression (Campbell 358). Another conclusion could be made that the stressful environment that led to the extinction of P. caudatum triggered histone acetylation of genes that enhances the ability to survive and reproduce in P. aurelia but not as successfully in P. caudatum. It might not be because P. aurelia had certain random mutations that proved better than the genes of P. caudatum but that P. aurelia had epigenetic changes (which could have been inherited from previous generations) that was its selective advantage. And since environmental interactions affect adaptations that organisms acquired through evolution (via random mutations, epigenetics changes, or both), we can conclude that communities evolve together, not individually.
ReplyDeleteMutations are the driving forces of evolution—whether in the genome or the epigenome. While mutations in the genome obviously lead to phenotypic changes in offspring, they are the central cause of genetic diversity. While mutations can be a source of complications ranging from the growth of a sixth finger to the conjoining of twins, such as the case of Abby and Brittany Hensel, there are many that are beneficial to humans that people may choose to preserve and pass down future generations. For example, there is the gene for sickle cell disease, which has the ability to protect carriers from malaria. This mutation is common in people of African descent, since malaria is so prominent in Africa, and only those carrying two copies of the gene would develop a stronger resistance to malaria, so it would be an evolutionary advantage to preserve the gene among a group of people with the same mutation in order to reproduce with a higher percentage of offspring having the mutated gene. Although sickle cell anemia is not necessarily a good disease to have because of its shortening of life expectancy, it allows carriers to build a tolerance towards the more deadly disease of malaria, and allows them to survive past adulthood to be able to reproduce at least once before succumbing to any other fatal environmental factors
Tracy Lai (tracymlai@hotmail.com)