Mystery of Genome

Page 139

Can natural selection create?

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repeatedly. But as we will soon see, neither can such a sequence arise randomly one nucleotide at a time. A pre-existing “concept” is required as a framework upon which a sentence or a functional sequence must be built. Such a concept can only pre-exist within the “mind of the author”. Starting from the very first mutation, we have a fundamental problem - even in trying to define what our first desired beneficial mutation should be! 2. Waiting for the first mutation - Human evolution is generally assumed to have occurred in a small population of about 10,000. The mutation rate for any given nucleotide, per person per generation is exceedingly small (only about one chance in 30 million). So in a typical evolutionary population, if we assume 100 mutations per person per generation, one would have to wait 3,000 generations (at least 60,000 years) to expect a specific nucleotide to mutate within a population of 10,000. But two out of three times, it will mutate into the “wrong” nucleotide. So to get a specific desired mutation at a specific site will take three times as long - or at least 120,000 years. Once the mutation has occurred, it has to become fixed (such that all individuals in the population will have two copies of it). For new mutations, because they are so rare within the population, they have an extremely great probability of being lost from the population, due to random genetic drift. Only if the mutation is dominant and has a very distinct benefit does selection have any reasonable chance to rescue any given new mutation from random elimination via drift. According to population geneticists, apart from effective selection, in a population of 10,000 our given new mutant has only one chance in 20,000 (the total number of non-mutant nucleotides present in the population) of not being lost via drift. Even with some modest level of selection operating, there is a very high probability of random loss, especially if the


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