For evolution to work, natural selection has to recognize and eliminate bad mutations, while recognizing and promoting good mutations. However, most mutations are much to small to make any detectable difference (they fall within Kimura’s “No Selection Zone” 2), and so natural selection cannot even see them. Since almost all mutations are negative (about a million to one), the genome of an organism will slowly degrade by thousands and millions of accumulating undetectable mutations which, by themselves, cannot be detected, but in the long run will result in genetic death. By analogy, you cannot see individual atoms on your car rusting at any one time, but over the years, it will destroy the car. 3
This analogy, provided by Dr. J. C. Sanford in Genetic Entropy: The Mystery of the Genome, is an excellent one for explaining why natural selection is very limited: 4
… let’s imagine a new method for improving textbooks. Start with a high school biochemistry textbook and say it is equivalent to a simple bacterial genome. Let’s now begin introducing random misspellings, duplications, and deletions. Each student, across the whole country, will get a slightly different textbook, each containing its own set of random errors (approximately 100 new errors per text). At the end of the year, we will test all the students, and we will only save the textbook from the students with the best 100 scores. Those texts will be used for the next round of copying, which will introduce new “errors”, etc. Can we expect to see a steady improvement of textbook? Why not? Will we expect to see a steady improvement of average student grades? Why not?
Sanford’s analogy demonstrates why natural selection can’t produce new information slowly over time. Because of natural noise, it is unrealistic.
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Sources
Sanford, J. C., & Baumgardner, J. (2008). Genetic Entropy & the Mystery of the Genome (3rd ed.). Waterloo, NY: FMS Publications.