A Guide to the tactics of Evolutionists

Hi randman You might consider the HIV virus, which arose in a single individual (or at most a small number of individuals) in the 70s or early 80s (I don't recall). At one point only one or a few people had it and there was naturally low genetic diversity in the HIV population because the population was small. Nowadays, however, after 25 million people have died of it, we have not only different strains of the virus in different geographical regions, but also different strains within a single individual! These are called quasi-species in the literature, and you can do a google search to find lots of examples of multiple quasispecies HIV developing within single individual hosts. If you don't think that this genetic variability arose through mutation in the face of opposing drift and selection, I would be interested to know where you think it came from!In experimental terms, it is difficult to observe the development of genetic variability in metazoa because it is just too slow to be practical. Professor Lenski has carried out some experimental evolution studies in which populations of bacteria descended from a single individual are grown for tens of thousands of generations and the mutations occurring are observed by gene sequencing. He finds that genetic variability in his populations does indeed increase over time; the extent to which it increases is greater than that predicted by phylogenetic comparison of different bacterial genomes, but less than that predicted by direct estimates of bacterial mutation rates. In any case, there is NO genetic diversity in the starting population because it consists of a single individual, but after a few thousand generations the bacterial populations have diversified as expected.And then of course we have lots of natural experiments with things like novel antibiotic-resistant bacteria, new forms of the flu and common cold every year, etc. These new forms arise somehow, and if it is not mutation then it's up to you to explain where you think the variability comes from. Because Lenski's experiments give solid evidence that mutation is indeed the driving force behind genetic diversification and drift/selection doesn't stop it.MickAbE - sorry, I forgot to mention that your view of selection only decreasing genetic variability is not an accurate representation of the theory. This is quite an important point. Positive selection is expected to increase the rate at which novel beneficial alleles are fixed in a population such that selected fixation rates may be higher than the "background" fixation rate due just to drift. You are only correct in thinking that natural selection solely reduced diversity if you limit yourself to deleterious mutations. When we consider beneficial mutations, natural selection will increase the rate at which species diversify. Hence in humans we find unusually high diversification rates in genes involved in the brain, olfactory system, genes involved in cancer, etc. and those fixed substitutions exhibit high dn/ds ratios indicating that selection is the source of that diversification. Again, if you think that this diversification is just due to drift or some other mechanism, you will need to explain the high dn/ds ratio.For example, how do you explain these findings? The key quote from the abstract of that article is: "A significant McDonald-Kreitman test showed an excess of fixed amino acid replacing substitutions between species, consistent with positive selection." An excess, not a deficiency as you would predict.One last edit - I do think that Dr Adequate's question about the Y chromosome is important. I've no idea whether you are a YEC or not, so this may not apply to you but it certainly applies to others on the forum. If one were to accept that all humans arose from a single reproductive pair (which amusingly is - kind of - the common belief of both evolutionary biologists and creationists!) then where does modern day genetic variation come from? If we start with Adam and Eve (for the creationists, or just Y-Adam for the evolutionists) there was by definition a maximum of four alleles for each gene at the very beginning of the human species. Now it is quite clear we have more than four alleles fixed across global populations for many genes - where did they come from?Edited by mick, : No reason given.Edited by mick, : No reason given.Edited by mick, : No reason given.Edited by mick, : No reason given.Edited by mick, : No reason given.

Hi randman, yes, I agree with you, but I think I made the point somewhere in the last post that there are practical constraints on the kinds of experiments we can do. We can "easily" breed bacteria for 20,000 generations but it is impossible to do the same experiment with chimps. That experiment would take pretty much all of human history. It's not really a criticism of the theory to say that such experiments have not been carried out on chimps or reptiles or whatever, since such experiments are physically impossible. As biologists we just have to deal with the data that we can obtain, and understand that there is a great deal of data that we cannot obtain in a direct controlled experimental fashion.I think if you were to respond to just one of the points in the last post it would be that of the dn/ds ratio, i.e the difference between purifying selection (which removes genetic variation) and diversifying selection (which promotes genetic variation). Your model of evolution appears to predict an absence of diversifying selection, yet studies of dn/ds ratio in modern day species seems to show that diversifying selection is quite common.If you would like more detailed explanation of what the dn/ds thing is all about, please just let me know. Otherwise, take your time in replying, no hurry.Mickin edit - Oh, one other thing - you said: if you want to make the argument that observed variation is "microevolution not macroevolution", then I think it would be fair for you to define precisely where you think lies the limit on the amount of genetic variation that can be generated by microevolutionary processes. Otherwise I will waste a lot of time looking up papers which you can just brush aside crying "MICROEVOLUTION!" I don't know how you would define such a measure, perhaps in terms of % nucleotide difference between the average pair of individuals in a population or something. But you have to make it clear otherwise this is just going to be a case of borders being redrawn every few posts...Furthermore, please bear in mind that your previous proposition that "natural selection only reduces genetic diversity" is quite different from your new proposition that "natural selection promotes genetic diversity only within the 'virus kind'". I'm happy for you to shift the goalpoasts a little bit, because I think that is where much productive debate resides, but you shouldn't gloss over it so easily when your argument evolves like that. But hey, I'm not going to make a big deal if your argument evolves, that is a healthy thing.One last point - I'm sorry I keep editing my posts after submitting them. I am posting here while doing some very boring "typing numbers into spreadsheets" kind of work and it's tempting to keep coming back. I promise only to edit posts until somebody replies to them, at which point I will stop.Edited by mick, : No reason given.Edited by mick, : No reason given.