Nice article. Say how about translating it to english one day? edo wrote: > In this context a polymorphism is a naturally occurring variation > in the normal nucleotide sequence of the genome within > individuals in a population, and an allele is one of two or more > forms of a given gene that control a particular characteristic, > with the alternative forms occupying corresponding loci on > homologous chromosomes. Variations are denoted as polymorphisms > only if they cannot be accounted for by recurrent mutation and > occur with a frequency of at least about 1%. > In general, a heterozygote is a diploid or polyploid individual > that has inherited different alleles at one or more loci and > therefore does not breed true. So you're saying animals at any point got any triploid heterozygotes?? I thought those were only present in plants... (BTW, diploid heterozygotes do breed true.) > In genetics, a "balanced polymorphism" is a genetic polymorphism > maintained in a population because the heterozygotes for the > alleles under consideration have a higher adaptive value than > either homozygote. > Prions are a class of poorly understood proteins implicated in a > number of exotic human neurological diseases and in some common > animal diseases such as sheep scrapie and bovine spongiform > encephalopathy in cattle ("mad cow disease"). Spongiform > encephalopathies are a type of brain disease found in humans and > animals and are characterized by macroscopic vacancies produced > by the disease process (the brain has a sponge-like appearance). > What is remarkable about prions is that they behave as infectious > agents, but they are 100 times smaller than viruses and their > mechanism of replication is unclear. Prions are nothing but complex molecules that, when specific circumstances in contact with a specific indentigrent (of a human braincell in this case) forms a duplicate of itself, in effect transforming your brain into a mass of non-functional hydrogen-bond connected prion strains. This is rather easy to imagine once you know the function of the average enzyme, but of course it has not been explained into detail as of yet. > One human disease in which > prions have been strongly implicated is Creutzfeldt-Jakob disease > (CJD), which appears to have a genetic basis in about 15% of the > cases. All the prion diseases are apparently associated with the > accumulation in the brain of an abnormal protease-resistant > isoform of the prion protein. In other words, an abnormal variant > of the normal prion protein is somehow copied or produced by the > disease process, which can be initiated by introducing infectious > prion into the system. > Of interest in this context, is the disease "Kuru". This disease > is similar to Creutzfeldt-Jakob disease, and is a human > spongiform encephalopathy. Kuru occurs only in the eastern > highlands of New Guinea, occurs more frequently in women than in > men, which apparently coincides with the customs surrounding > cannibalism in a society where the remains of dead relatives are > handled and eaten primarily by children and women. After > cannibalism was outlawed, the incidence of the disease decreased, > and the current consensus is that cannibalism was the primary > mode of transmission of the pathological agent. You've got a problem here. CJD is a disease that was in effect generated in the cow society, while Kuru was likely cultivated in human society or maybe at some point in time jumped to human from something those people eat. > The following points are made by John F. Brookfield (Current > Biology 2003 13:R592): > 1) The patterns of DNA sequence variation in human populations > are the result of migration, selection and random genetic drift > operating, as a function of the effective population size, on > human populations over the last million years. Given this, the > possibility exists of using the structure of the human > variability to infer something about human migration, selection > and effective population sizes in the past. A new study of DNA > sequence variation at the prion protein locus (Mead et al: > Science 2003 300:640) has been interpreted as suggesting a > sustained heterozygote advantage created by a lifestyle of > habitual cannibalism, implying a new vision of the lifestyles of > our ancestors. Ok... > 2) One of the most challenging questions about humans is to know > the extent to which natural selection operating in our > prehistoric ancestry has shaped our present phenotypes and > behavior. Evolutionary psychology tries to explain human > behavior in terms of the selective advantage conferred by > individual behavioral traits. This approach falls into the > biological tradition of trying to explain aspects of an > organism's phenotype through the fitness advantage that the > phenotype generates. With humans, however, the explanation of > behavior in adaptive terms is more difficult than in other > species, Ahem! Likely, it is just as complex as with other species, of course none of the scientist had gotten the idea to doubt it so far however. For example the obvious degenerations of capability to produce certian vitamins in our liver at first glance seems like a degeneration due to the lack of importance of that fact amongst humans in a given society, however it is also true that if you simply take into account the practical fact that with the obtaining of these vitamins (or their provitamin stages) thus removes the need to waste energy to synthesize them, the evolutionary point of degeneration of those abbilities is also reached. > as the societies in which we live today are immeasurably > different from those in which our gene pool evolved. While we may > be adept at hang-gliding, the genes that make us so were > unquestionably not shaped by selection against individuals who > hang-glided unsuccessfully in our evolutionary past. And so is it with all the animals, but who cares. > 3) For this reason, selective explanations of human behavior > cannot be judged on the basis of the consequences of the > behavior for modern humans, but only in terms of whether the > genes responsible would have been favored by selection during > the prehistoric eras when our genome evolved. For this reason, > many have speculated about the "environment of evolutionary > adaptedness", the hypothetical pleistocene environment to which > our genes were adapted by selection. While some insights into our > lifestyle during the time of the environment of evolutionary > adaptedness can be gleaned from studies of hunter-gatherers > living today, and from the archaeological record, this can never > be known with certainty. This is obviously a problem for the > adaptive interpretation of human behavior, as it is very easy to > hypothesize selection having operated on any arbitrary behavior > by making appropriate guesses about the nature of the environment > of evolutionary adaptedness. Lucky we sometimes got the chance to look into actual archeological fact and not just drift off dreaming how things should be... Remember how Leonardo drew the male reproductive organ in his time? The sperm comming trough the spine from the brain? He did that because he thought it was the way it should be. Don't do the same mistake twice. Please. > 4) In summary: A new study of genetic variation in the human > prion protein gene suggests that balancing selection has operated > on an amino acid sequence polymorphism in the gene during the > last five hundred thousand years, and suggests this is a legacy > of widespread cannibalism by our ancestors. In summary: Unless you show me a prion or heterozygote or anything like that from an archeological find, I'm not beliving a thing. FACT is what makes a hypotesys a theory. -- I could run like the wind just to be with you. Observer aka DustWolf aka CyberLegend aka Jure Sah C'ya! -- Cellphone: +38640809676 (SMS enabled) Don't feel bad about asking/telling me anything, I will always gladly reply. "Yes, Master." Have you been told Internet will always be threatened by worms viruses etc? We don't think so: http://208.186.111.189/ici/index.htm MesonAI -- If nobody else wants to do it, why shouldn't we?(TM)