EDITED PROMPT:
On page 122, Coyne paradoxically states, "genetic drift is not only powerless to create adaptations, but can actually overpower natural selection." Explain the process of genetic drift. Coyne mentions that genetic drift can cause features that don’t help or hurt the organisms. Then, what is the point of genetic drift? Distinguish between genetic drift and natural selection; in your response discuss randomness and lawfulness. Relate your response to a biological theme.
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What we have to recognize first is that genetic drift is the opposite of natural selection. That is, genetic drift also produces change in allele frequencies, but randomly, whereas natural selection causes changes in allele frequencies based on what genes and traits are beneficial and ensure the fittest organism, thus increasing chances for survival.
ReplyDeleteWhen discussing this point, Coyne bring up the fact that “as a purely random process, genetic drift can’t cause the evolution of adaptations. It could never build wing or an eye.” (123) Natural selection, however, CAN build a wing or an eye based on mutations that prove advantageous to an organism. On the other hand, genetic drift can still cause the evolution of features, but these features are neutral- they aren’t harmful, but they don’t provide a selective advantage of any kind, and therefore aren’t adaptations.
To the point of genetic drift overpowering natural selection, in small populations if the proportion of an allele increases by chance but is harmful, basically this is a force against what natural selection is trying to work at. Coyne brings up the example of high incidence of genetically based disease in humans where the people live in isolated communities. Here the frequency of harmful genes increases by the sampling effect (offspring are playing the lottery in terms of gene selection, and many kids may happen to draw a bad gene by chance), even though natural selection is fighting this and favoring ‘healthy’ individuals.
In terms of relative importance, I would say natural selection is more important in the context of evolution as a whole. Although it is true that drift produces genetic change and evolution, it is random and unpredictable. Also, oftentimes this drift doesn’t help or hurt, so it is left alone. On the other hand, natural selection is responsible for the evolution of new species, and important adaptations that enable current species to survive and reproduce. If we only evolved by chance, species would die out when faced with tough environmental changes. We’d have to cross our fingers that the frequency of genes that allowed the move from water to land would increase by luck; thanks to natural selection however, organisms developed adaptations that ensured the move was possible and successful. Relating this to what we learned about endosymbiosis, what if that was left to chance? What if not enough photosynthetic cyanobacteria were randomly ingested? We wouldn’t be able to have complex organisms. However, natural selection favored this, because organisms that could undergo photosynthesis had a selective advantage. This relates to the theme of continuity and change because some of the change we see over time is in fact random, but on the other hand a lot of the change we see can be attributed to natural selection favoring the fittest genotypes.
(additional source used: http://www.actionbioscience.org/evolution/futuyma.html)