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A couple of genetic factors may correlate to increased variability in response to stress. However, these are not inherent in the punctuated equilibrium model. They also do not require or suggest any intelligent reasoning to deal with the problem.
One proposed scenario for large, abrupt evolutionary changes is based on the role of heat-shock proteins (HSP). These have several regulatory functions, including acting to chaperone other proteins. The influence of the HSP may conceal the effects of a mutation in the other protein. However, in a cellular emergency (such as heat shock), the HSP proteins are transfered to damage control and other more pressing needs, leaving the others unchaperoned. As a result, accumulated concealed mutations may be expressed. The articles that I have seen relating to this idea have shown experimentally that such emergencies can reveal hidden mutations, but I do not know of any experiments that subjected the mutations to further evolutionary pressure.
Another, more substantiated mechanism was discovered in study of bacteria that seemed to show Lamarckian evolution. The bacteria seemed to mutate more quickly when under stress and then to "remember" to mutate quickly when the stress was repeated. However, it turned out to have a better explanation than smart bacteria. The experiment involved making bacteria unable to feed on lactose, putting them on lactose, and seeing what would happen. Under the initial stress, the bacteria could not multiply. Although each individual bacterium was stressed, there was little competition. Thus, normally unfavorable mutations that would usually be outcompeted were able to survive. One mutation occurred in a gene that affects DNA copying and error checking. This greatly increased its mutation rate, normally a bad thing but in this situation its only chance. One of the resulting mutations fixed the lactose-utilizing gene. As they already had a high mutation rate, the successful bacteria quickly recovered when the experimenter modified the lactose-utilizing gene again. A similar pattern occurs in cancer. Although high mutation rates are generally bad for cells and produce a lot of inviable cells, rapid change is the only way for cancer to stay ahead of the body's defenses. However, the cells have no way to try to become more prone to mutation. Rather, the individuals that happen to have a suitable mutation are able to succeed.
Such situations, in which natural (or artificial) selection favors high levels of mutation, may account for some of the patterns of punctuated equilibrium. When a new opportunity opens, or the current niche for an organism becomes less favorable, the individuals that have higher mutation rates may be more successful. However, in relatively uniform conditions, individuals with low mutation rates will generally be more successful, by sticking with an established successful genome for the environment. Thus, we will see bursts of variation in organisms, often associated with times of environmental change, and long periods of little change. However, most punctuated changes are on relatively small scales, and do not require a large genetic shift.
Depending on the ratio of science to fiction in your writing, you could envision an organism that was capable of deliberately manipulating its mutation rate in response to perceived need, but there is no evidence for the existence of such ability.
Dr. David Campbell
Old Seashells
University of Alabama
Biodiversity & Systematics
Dept. Biological Sciences
Box 870345
Tuscaloosa, AL 35487 USA
bivalve@mail.davidson.alumlink.com
That is Uncle Joe, taken in the masonic regalia of a Grand Exalted Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at Droitgate Spa
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