Posted by James on 10/18/2007, 2:48 pm, in reply to "Re: Infection Worse than AIDS" Mutations do not occur in response to the environment. They occur randomly, however, they are selected for or against by the environment as those with weaker traits do not survive to spread their genes within the pool. Thus, allele frequency changes, which if continued due to a more permanent change of environment will result in a new species. In the case of the bacterium, we are not observing a random mutation. We are observing certain genes (alleles) within the population being selected by the fact that those organisms with those genes survive the antibodies and pass on their genes to the next generation. Now, the generation after the bulk of the first generation has been obliterated will have a greater number of the alleles with the genes for surviving the antibodies that nearly wiped out the earlier generation. Since the bacterium's environment is constantly being hit by antibiotics that kill off those organisms without the proper genes for immunity to the antibodies, each successive generation will continue to have more and more numbers of organisms with the resistance. At the same time this is occuring, the genetic composition of the organisms is adjusting to the new environment. In other words, not only is the number of resistant alleles increasing, but at the same time, their genetic makeup is experimenting (for lack of a better word) with the gene sequence that gives resistance. Those organisms that are fortunate enough to get the new genes with stronger resistance will naturally survive better than the others, thus passing on a stronger resistance to the next generation. And the same allele frequency response as earlier will work out in the same way. This is evolution at work in the most basic and easily understood means. Most other understandings of evolution are off on this. As far as an impending human epidemic, the way I see it is that we humans are actively forcing the hand of bacterial and other organism's evolution, thus making them stronger, while at the same time hampering our own natural immune responses. And someday, that will come back to haunt us.
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"My understanding is that genetic mutations do not occur in response to anything except random chance. Only AFTER the random mutation has occurred does selection by the environment occur."
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