contrarian
Registered Senior Member
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"Mutations are commonly said to occur "randomly". However, as we have seen, mutations do not occur random with respect to genomic location, nor do all types of mutations occur with equal frequency. So, what aspect of mutation is random? Mutations are said to be random in respect to their effect on the fitness of the organism carrying them"
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Li and Graur, Fundamentals of Molecular Evolution, 2000"
From the quote above, it seems a reasonable definition of random with respect to fitness(R wrt F) mutations is mutations which take place at the same rate regardless of whether they are fit and nonfit *when everything else is equal*. One way of measuring this would be for the exact same (physical) mutation one would expect the rate of its occurence to be the same in environmental conditions where the mutation results in a fit phenotype as when environmental conditions cause the phenotype to be nonfit.
Given this definition, I don't believe that 1. there is ANY scientific evidence for random wrt fitness mutations and 2 I believe there is SOME scientific evidence for nonrandom wrt fitness mutations.
My argument for 2. is based on a simplified (for argument's sake) take on starvation induced hypermutation, whereby a starving bacteria increases its mutation rate when it is starving. Let's say that a hypothetical bacteria has 1000 possible (physically)mutations, each of which have the same probability of occuring as any other mutation at any given time.
Let's say that while the organism is not starving it has the following possibilities for its mutations to affect fitness. 990 mutations will be neutral(no effect on fitness), 9 will be negative(reduce fitness) and 1 will be fit(increase fitness). Upon starvation, however, 998 mutations will be neutral and 2 will be fit. Since the bacteria is already starving, its fitness cannot decrease(it cannot reproduce at all) and I will say that a previously neutral mutation will improve digestion(possibly by allowing digestion of a different food source). If starvation causes a doubling of the mutation rate and the bacteria starves 1/2 the time, we can analyse the relationships that exist btw mutations and their fitness.
Non starving 989 neutral 9 negative 1 positive
Starving 1996 neutral 0 negative 4 positive
If we measure the occurence of the mutation that changed from neutral to fit under starvation conditions, we see that it takes place twice as often when it is fit. Likewise a mutation that moves from negative to neutral under starvation will happen twice as often when its fitness value is higher than when it is lower.
Now, as far as I can see, even this simplified(IMO uncontroversial) exercise shows that mutation is sometimes nonrandom wrt fitness, so it appears that random mutation is falsified.
Any comments?