Kleinman said:
Examples of nutrient deficiencies are so commonplace that I didn’t think I had to give any examples. In humans, multiple nutrient deficiencies are very common, for example in alcoholism, starvation, fad dieting and so on. Dietary nutrient deficiencies also occur in the wild.
And these somehow limit evolution? How? Your argument was that these multiple pressures limit or eliminate evolution, was it not?
I've seen plenty of multiple minor deficiencies. They tend to do fairly little clinically, but may have effects on reproduction (obviously important for the evolutionary process). I've seen plenty of multiple major deficiencies. They
tend to do one thing -- lead to death. Death seems to me to be a very big part of evolution. Those who do survive the process of these multiple deficiencies tend to do so for only one reason -- variability or new mutation that allows them to survive. Funny, that.
Kleinman said:
So, you are taking the position that only a single selection condition drives evolution at any given moment. Do you want to describe to us what the selection condition that evolves a gene from the beginning?
OK, I'll spell it out.......what you are describing with the antiretrovirals are selection pressures that tend to lead to the death of species. The pressures are immense for this particular virus. The fact that they work tells us something important -- that we have found a significantly profound pressure that has beaten back this virus somewhat. If you provide significant enough pressures you can kill or beat back anything. The number of pressures is not necessarily the magic ingredient. If we have a bacterium that uses glucose but has a pathway that can activate galactose metabolism, then the absence of glucose will not kill it. But if we remove glucose and galactose then the bacterium is in serious trouble and will likely go extinct unless there is a variant that uses another food source and takes over. If we have a bacterium that will not produce quite as many offspring if glucose is not present and not as many offspring if galactose is not present, then this will not be absolutely fatal, even in the presence of both deficiencies. It is likely that some variant will arise in that situation to use another energy source eventually though. Of course this process will take longer than the deficiencies that tend to be fatal. While multiple pressures may be fatal or severely limiting, other variants of different types of pressures will not. It depends critically on the type of pressures involved. Concentrating on the number and thinking of it magically is silly. These pressures are generally not absolute -- we see relative deficiences of certain foodstuffs rather than complete deficiences. The situation with multiple reverse trancscriptase inhibitors is most akin to a complete or near complete deficiency of some resource that keeps the organism near the brink of extinction. Or, rather, it is like a severe hit on the gonads of any vertebrate -- eliminate the possibility of reproduction. This should eradicate the organism, but it hasn't in this case (damn retroviruses). HIV is a special case in many respects. I don't think you can draw many conclusions from the type of pressure being placed on this virus except that if you slow reproduction, then you slow reproduction. I see nothing that tells me that other pressures would have the same effect.
And, no, I have no number of selection pressures in mind. I don't think it even makes sense to think that way as an absolute. There were undoubtedly times when one pressure for early organisms was important and other times when multiple pressures came into play.
Just because antiretroviral drugs primarily target reverse transcriptase does not mean that each drug works in the same way. Ultimately, the strategy for the using multiple drugs is to slow the reproduction of the virus and minimize the appearance of drug resistant strains of the virus.
Um, yes, in the broad sense it does. That is what we mean when we use the term "mechanism of action". They all target the same enzyme system. They have different sites of action, so one drug may continue to work when resistance to the others forms. Eventually this will mean that none of these drugs will work. Eventually the virus is going to win. We already know it will win. It's beginning to win already.
So tell us, what was the selection pressure that gives rise to the hemoglobin gene and molecule? If it is as Paul previously suggested, the presence of oxygen in the atmosphere, describe that selection pressure so that it can be put in ev and evolve the hemoglobin gene.
I'm sorry, but what does this have to do with anything I have said or your use of HIV as the example par excellence? I do not pretend to knowledge that I do not have. I would need to study the problem before even beginning to suggest alternatives. I do not know the history of the molecule and its progenitors well enough to say.
It is the secondary infection that usually kills the person infected with HIV so treating the secondary infection prolonged life slightly. It wasn’t until combination therapy was introduced that real selective pressure was put on the virus (unless you count the 20 or so selective pressures you speculate are placed on the virus by the person’s own immune system). This selective pressure has altered the HIV virus. Mutated HIV reproduces at a slow rate than the wild virus.
I know the history, I watched it happen. Support for the secondary infections initially prolonged life only for short periods of time. As time progressed and before triple therapy was begun people were already living longer. The virus was already becoming less virulent before triple therapy was introduced. It mutated because it killed people too fast and less virulent strains were able to be transmitted to others. AZT caused a huge pressure on the virus to mutate. That pressure alone resulted in big changes, not all of which have or can be quantified. Triple therapy has produced changes as well. It continues to do so. Evolution has stopped, though?
It’s not the way I define it, it is the way reality works. Certainly there is an immune response to the virus, antibodies to the virus are detected. However, this immune response is almost universally ineffective. Once the retroviral therapy is initiated, it would not surprise me that the person’s own immune system contributes to the suppression of the virus.
I'm sorry again, but I cannot understand what would possess anyone to think that the immune response is the only host reaction to the presence of the virus and the only selection pressure.
Bottom line........HIV is a bad example.
