What is the mechanism that prevents microevolution to become macroevolution?

We have our theories but no way to prove them. Mine has been based on the observation that all* the processes of evolution -- except mutation -- involve a reduction in genetic diversity, and that if these processes continue to split and diversify populations, the end result will be exremely decreased built in ability to evolve further because of the extremely limited allelic possibilities. Prime example is the cheetah with its single-allele situation at many loci. Just no other alleles possible. Reproduction can only pass on the one allele. Offspring have so little diversity they are virtually clones of the parents. This is an extreme but it illustrates the end result of the processes that lead to "speciation." Speciation is therefore not the genetically rich or open-ended thing you'd expect to find if evolution were true but in fact a stopping point. I started the thread "Natural Limitations to Evolutionary Processes" to explore this idea.I'm also intrigued by mjfloresta's discussions. He/she seems to argue from the observation that for all the multiple variations we see, say for example in dog breeding, we never see a variation that changes what he/she calls the basic "body plan." That is, a dog is always recognizable as a dog, as having the basic body plan of dogs. I intuitively appreciate this observation although I suspect it's going to be hard to defend. I look forward to the working out of this idea on her/his thread, and whatever she/he might say here.{EDIT on 9/4:
* When I say ALL the processes of evolution (except mutation) involve a reduction in genetic diversity, I'm overstating it as I often do. The idea is that the overall TREND of all the processes of evolution is reduction in genetic diversity (loss of alleles in the population). Of course many of these processes only shuffle the existing alleles and don't eliminate any, and in one case, hybridization, there is in fact an increase in alleles and therefore in genetic diversity, but this does not involve the addition of anything new; it is merely the reintroduction of alleles formerly lost between the populations. With this one exception, and keeping in mind that many of the processes merely shuffle and do not eliminate alleles, I'm saying that over time the general trend is nevertheless to reduction in genetic diversity through elimination of alleles. This is because those processes that do this are quite common and most populations eventually undergo them; that is, the processes that select, the processes that bring about a small new population and so on.This scenario is explained many times in the thread.And of course I'm arguing that mutation does not occur in enough numbers or to enough beneficial effect to make more than a negligible or destructive contribution to this whole scenario.}.Edited by Faith, : No reason given.Edited by Faith, : No reason given.Edited by Faith, : Edit noted in text

Funny how long it took to get that acknowledged, however. You do know that all those selective and recombination processes are labeled "evolutionary processes" although what in fact they do is reduce genetic possibilities.Yes, the entire theory of evolution rests on mutation as the driving force. Is it up to its role? Well, considering that MOST observed mutations (as opposed to those simply assumed by the theory to have brought all useful traits into existence) are deleterious or useless, this is debatable.Edited by Faith, : No reason given.

This makes for extremely high goalposts considering that evolution was considered science before anyone had a clue about DNA or what a mutation was.{EDIT: I wrote a better answer to this post in Message 146Edited by Faith, : No reason given.Edited by Faith, : No reason given.

A bottleneck is simply an extreme type of "evolutionary process" that drastically brought about what is normally a much more gradual kind of change over many more speciation events. One gets you there faster than the other, but both are going in the same direction.

I figure that whatever it is in the genome you expect to see as evidence of a bottleneck of the magnitude of the Flood is simply misinterpreted. I'd be looking at all that junk DNA myself.

Please specify exactly what this genetic evidence looks like if it's so obvious.We know about the cheetah's severe bottleneck by the fact that it has an extreme scarcity of alleles for a great number of genes, but this is unusual and shows a very recent bottleneck. What would you expect to find from 4500 years ago?I think evidence for the Flood bottleneck is probably in the junk DNA.Edited by Faith, : No reason given.Edited by Faith, : No reason given.Edited by Faith, : No reason given.

I understand junk DNA or pseudogenes to be nonfunctioning DNA that previously had a function. Dead DNA. So much defunct DNA in the genome may suggest to an evolutionist previous incarnations as other creatures, but to a creationist it suggests a lot of death of human beings over the millennia, and the death of a lot of genetic material too, by killing off all the viable alleles for those no-longer- functioning genes. I don't know how the genetics of it works exactly but that's the ballpark idea.But let me ask YOU what you expect to see genetically that would demonstrate an earlier bottleneck? It's been asserted here that it is easily recognizable in the DNA. Is it? And what does it look like? How would a bottleneck be "obscured" over time, as you suggest? This does imply that you expect it to be something specific when it's fresh.Added by edit: You asked: OK, so you wouldn't expect to see "patterns of diversity" if there had been such a bottleneck?Well, my answer to that is there is still a lot of diversity in the functioning DNA.The cheetah is merely an extreme caused by a much more recent bottleneck, which is why it is down to one allele per locus. But there was still a lot of genetic potential in the individuals on the ark -- how is unclear, larger genome is postulated.Edited by Faith, : No reason given.

I've read that kind of stuff already, That article you linked . No way those estimates of tens of thousands of years can mean anything to me; just a fantasy of theirs based on a different set of expectations. Obviously they can see *something* there, but their numbers are no doubt skewed by their denial of the first great "bottleneck," the starting of all human beings from Adam and Eve, as well as the second at the Flood.*You too of course have a different set of ideas about the history of DNA on which to calculate how much diversity you would expect to see.No, you are wrong, I'm not saying diversity shouldn't be there. You are. I've many times acknowledged that there is still a lot of diversity left.Yes, the mere fact of death itself would over time kill off a lot of genetic material. But we only have 1% functioning DNA left. That suggests to me that the great flood bottleneck is probably reflected there. * They are addressing "anatomical and archaeological" evidence for this supposed bottleneck. I wanted a GENETIC indicator of a bottleneck since others here, jar anyway, claim it's so OBVIOUS. The article says that "Such an event would be expected to leave a significant mark across numerous genetic loci and observable anatomical traits" -- well, what SORT of "mark?" What's wrong with all taht junk DNA as such a "mark?" I mean billions of human beings died in that event; it should have left a pretty dramatic "mark."Edited by Faith, : No reason given.Edited by Faith, : No reason given.Edited by Faith, : No reason given.

Oo, this is interesting from that article you linked : Yes, of course. THAT'S WHAT SPECIATION DOES, IT SEVERELY REDUCES GENETIC DIVERSITY. That's what a bottleneck is, severely reduced genetic diversity.Edited by Faith, : to add link

This has been discussed quite a bit at EvC and it's not as nutty as you are making it out to be. I believe MJFloresta goes on to explain this quite well, but I'll try it myself. Sometimes I state it too baldly as I did above, but sometimes I'm clearer that I mean that this is a trend. It may take a lot of time, many generations, or in the case of drastic population splits, which is what a bottleneck is, no time at all.The tendency of all the evolutionary processes EXCEPT MUTATION -- and recombination, but in a different way -- is to the reduction of genetic diversity through the elimination of alleles from the population. Recombination of populations may provide a temporary increase, and in fact change the character of the combined population in a way that could be called speciation, but this does not involve anything novel, merely the shuffling of allelic possibilities that are already present in both populations. Only mutation can introduce something truly new, and of course we challenge the idea that it does this, if at all, to a degree that would overcome the depleting effects of population splitting.Now, population splits don't always lead to new species, but they are always working in that direction. In the case of ring species, for example, they are actually called species because they don't interbreed. You can identify each group by specific differences from the others. These differences are caused by the differences in allele frequencies brought about by their separation from a previous population. The old population may also have new frequencies and therefore change after the split too, but that depends on how many left.The split may do no more than shuffle the frequencies of the alleles with no actual loss of alleles, but that depends on how much the population is split. A very small number leaving a big population is not likely to have all the alleles of the parent population, so they experience an actual loss of allelic information in the new population as a whole. Then alleles that weren't much expressed in the parent population may become prominent and create a new phenotype distinguishing it from the previous popuolation, perhaps quite dramatically.When it leads to a population that doesn't interbreed with the parent population this is called "speciation." The point is this speciation is brought about by the loss of allelic information. Without this loss there would not be any speciation at all because all the same alleles would continue to keep the phenotype the same as in the parent population. {Edit: OK I overstated this again. The change may be brought about without an actual loss of alleles, merely a change in frequencies, but often there is such a loss, as when the new population is appreciably smaller than the parent population.}I'm talking about what happens when populations split. Basically the same thing happens with any clear selection process that isolates members of a population from others. Natural selection may do it by favoring a few when all the others die (antibiotic resistance in bacteria happens this way), or migration of small portions of a population to form a new population, as in the case of ring species, or quite a drastic split such as bottleneck. Bottleneck is merely the most drastic of the processes, but they all tend in the same direction. Again, the smaller the new population the greater the loss of alleles in the new population as opposed to the parent population, the less genetic diversity therefore, and the more the phenotypes differentiate and tend toward speciation.That's what the splitting processes do. These processes are called "evolutionary processes" in most sources I've found. They are recognized as leading to speciation, just as the formula about evolution as a change in allelic frequency is. What seems to be left out of the formula is this general tendency to allelic depletion and reduced genetic diversity over time.The other processes are immigration or recombination and mutation. The former, as mentioned, just shuffles the alleles together and may create a new phenotype, but without adding anything new. It's a sort of stasis.Mutation, again, is the only possible way new information could be added to a population, and that's why attention then goes to the nature of mutation, whether it can really support this role.{EDIT: All this assumes a given number of alleles in the total gene pool of the kind. Mutation is going to alter this number of course, but that has to be discussed as a separate topic to avoid confusing things.
Edited by Faith, : No reason given.Edited by Faith, : various grammatical improvements for clarityEdited by Faith, : No reason given.

No, of course I didn't read the whole abstract -- I don't know the terminology well enough to read that much. I copied out the whole paper and cleaned it up to make it easier to read but I don't suppose I'm going to be getting through it any time soon. Really, you shouldn't just give a link to such a technical paper. You should explain clearly what it says in ordinary English when you are talking to non-scientists.Edited by Faith, : No reason given.

Well, that's a reason not to ask questions about it. I don't really want a whole new thread or an extended sidetrack in this thread either. The last two threads I tried to start for the purpose of getting a handle on some technical information backfired in very odd ways. Yours on mutation was way over my head and not really focused on beneficial mutations, mine became a debate which I hadn't wanted to happen, and the one on recognizing geological time periods has become geology 101 and may never get to recognizing time periods.I tend to expect that it should be possible to give some simple explanations I could follow right here in context, a few paragraphs describing in layman's language just what they covered and why it matters. Struggling through the paper on my own I don't really see anything that directly deals with what we are discussing here.

Listen, depletion of genetic diversity is a real problem faced by conservationists. What is a fantasy -- utterly without evidence, simply assumed -- is this idea that mutation drives evolution. The reason I leave it out is to bring to the fore the actual effect of the OTHER "evolutionary processes" which do reduce genetic diversity. Mutation needs to be discussed separately.Just wanted to say this much now. I will try to get back to your post later.

You are talking about ONE kind of experiment with bacteria and ONLY bacteria, correct? Yes that one shows that mutation alone can bring about microevolution, but it also raises the questions just what mutation is {edit: Is it really a mistake?, is it really random?, is this one in bacteria really a mutation at all?} and whether the same kind of thing can be shown in any other organism.In a population of chipmunks (thinking of a ring-species example from many months ago}, for instance, the main cause of phenotypic change from one population to another is the shuffling of already-present alleles brought about by a splitting or selection process, and often this involves the actual loss of some alleles to the population, even both old and new populations.There are so many alleles already present in such a population there is no need for mutations to fuel microevolution {and how would you recognize a mutation in such a case anyway? If you breed a population from two chipmunks then you can control the number of alleles, but how often does a mutation show up to make your point in that case?}. The problem is, as always, identifying the ACTUAL action of mutations in such a population. You can't merely assume any particular role for them. Edited by Faith, : No reason given.Edited by Faith, : No reason given.Edited by Faith, : No reason given.

About the black and the brown socks, isn't it true that some genes have a LOT of alleles in some populations? So if the population splits a particular gene may lose some alleles. Also that one orange pair is probably left over from a previously larger number in a previous population, and may still exist in a large number in a cousin population, since splitting has no doubt already occurred to create any given population. How do you KNOW that new alleles are generated, that is mutations that actually make a change and a change in a useful direction that gets passed on? There is no NEED for mutations for change to happen anyway. It's the natural result of the variety of alleles already present in the population. All of this happens merely with the given complement of alleles already in the population. There is absolutely NO evidence that any of this depends upon mutation, or that mutation even occurs at any rate that would contribute to the process. Edited by Faith, : No reason given.