Complexity of gene codes (Introduction)

by David Turell , Monday, August 16, 2010, 18:41 (5021 days ago) @ dhw

David has referred us to two websites, both of which as a non-scientist I find puzzling. > 
> The second article, available only in summary to non-subscribers, is on: 
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> http://www.sciencemag.org/cgi/content/summary/329/5993/740
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> but David has kindly provided us with salient extracts. It illustrates "positive selection", e.g. Tibetans adapting to high altitudes in "just 4000 years". David says that this "is a much faster rate than the known rates of random mutation and natural selection can provide. Therefore, it is concluded there are subtle mechanisms that can push adaptive evolution."
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> Firstly, I don't understand the relevance of random mutations anyway. Why on earth would Tibetans have randomly acquired an ability to cope with high altitudes prior to being exposed to such an environment? Doesn't common sense tell us this is "adaptative evolution", not random mutation? 
 
Of course it is adaptive evolution. Just as Reznick's guppies take two years to adapt to danger. The Tibetans migrated uphill and forced the adaptation. They didn't have to wait for random help from cosmic rays, or some other chance mechanism, creating a mutation. As stated yesterday in discussion with George, Darwin made some amazing guesses, but could not know what we are finding today. This type of research started in the early 1990's, and has developed quite a story of adapability, directed changes, not chance.->
> Also I wonder how the researchers hit on the figure of 4000 years. If you take that as the equivalent of say 200 generations, it seems a mighty long time for the Tibetans to be huffing up and down. (I'm not disputing the arguments of the experts. I'm just explaining why I don't understand them, and I'm asking for help.)-I don't either fully. It is done by identifying genes, and studies of changes from the past. I know I can go to 11,000 feet and walk around. I've done this at the top of Pike's Peak after taking the cog railroad up. I know if I stay there I'll get more red blood in my system and acclimate in a few days. I've done this at Cusco, Peru at 10,500 feet and then went to Machu Picchu at 8,500 feet very comfortably, toured Quito, Equador at 11,000 feet, over a two week period. And we started at Lima, at sea level. This is done by rapid temporary adaptation of the body, but eventually genes should take over and make the adaptation permanent.-
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> Secondly, as we have said repeatedly on this forum, the mechanism allowing for potential adaptation must have been built into early forms of life ... otherwise there would have been no evolution ... and so I can't see what is so revelatory about "positive selection". Right from the start of evolution, natural selection has meant the survival of those features that are best adapted to the environment, and this has to be "positive". Negative selection ultimately means goodbye.-I think it is a matter of bowing to Darwin verbiage: natural selection has both positive and negative sides to it, depending upon genetic response rate to adaptation. Too slow and you are gone as I previously stated: 
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> Geneticists are now showing us that the genome is responding actively to environmental pressures, not passively as Darwin expected. [...] Chance mutation and natural selection are a totally passive mechanism. 
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> Of course Darwin didn't know what we now know about genetics, but he certainly viewed adaptability as an integral feature of living things. but again I don't see what this has to do with chance mutation, which seems to me to be a totally different subject from adaptation. I'd always thought of the former as a random, entirely internal change (which may or may not be useful), and the latter as an internal change arising from interaction with external conditions. Am I missing something here?-Only that the "positive selection" proposal implies that there are internal processes that can change the genome to respond quickly to external pressures of the environment, immediately as those pressures are recognized. They do not allow the negative possibility implied in relying upon 'natural selection' alone to act in a random fashion.