What is the mechanism that prevents microevolution to become macroevolution?

The terms aren't used all that often in biology but I have seen them used. They are defined as:microevolution: any changes to the population genetics that does not produce a speciation event.macroevolution: changes producing speciation and from then on.Then nature of the changes may be exactly the same; that is, any one of the number of different kinds of mutations may occur and not be sufficiently different to produce speciation but exactly the same kind of mutation (simple substitution etc) might happen to force a speciation.In actual practice, of course, single genetic changes do NOT produce successful speciation. Even if they produce a successful individual a "real", total speciation would (as in the oft given creo strawmen) an individual with no one to breed with.This has, however, still be observed in plants that don't kneed a breeding partner.It isn't, for the most part, the genetic changes that allow speciation to happen. This is way it really is of value to discuss micro and macro evolution. It actually does, most of the time, require some other mechanisms to allow speciation to occur.The most obvious is geographic separation. With a population split into two between which there is no (or very little) gene flow the ongoing genetic changes which have to happen are not "smoothed" out but rather can accumulate in each of the populations.Over time the accumlated differences gradually reduce the likelyhood of the success of any pairings from the two populations. The time frames can be very short for some organisms (generations) and, more often, very long (millions of years) for others. Eg tigers and lions have not yet completed the total separation.The accumulated differences are, just like the changes of microevolution, the same set of kinds of mutations that always occur.There is no difference in the nature of the changes on either side of the line. The only difference is that gene flow is not (for some reason) available to keep the populations more or less homogeneous.This is what the "kind" folk don't seem to grasp or deal with. They look at the over all phenotypes but don't see that the genetic changes between even rather widely separated branches of the tree of life just more and more of the same thing.I'm not totally sure but I think there has been a few decade old history of the creationist idea of "kind". Once upon a time it was a species just as it is clear the bible means. As speciation events became demonstratable they backed "up" the taxonomic chart and have also gotten very fuzzy. They've been forced high enough up that humans and the other primates become one kind so they start to waffle. It is most amusing to watch.Kind must be defined in terms of genetics but there isn't anything there to point at.

Does the 96% similarity between us and chimps suggest that a very high degree of overlap can remain for a long time?

If you take the definition of "reduced diversity" in the way that you describe then the statement that diversity may be reduced by allopatric(geographic) speciation is true. But that is meaningless. "So what?" is the only thing that seems to come to mind.The total diversity of the organism has not reduced at all when the split first occurs and, at first, they are still one species.Faith makes some big deal about allele reshuffling being able to force the speciation and I don't know (and she doesn't either) if that is possible or not. I suspect it can but again "So what?" it just helps allow for speciation even in the absence of mutations.Once the geographic separation has occured new mutations will not be spread through the entirety of the populations of the organism (either by drift or selection). New mutations DO occur.By the time speciation has actually occured the two populations will not only not have a lesser sum total diversity they will have a greater.To try to pick a very specific case where one of the populations happens (perhaps because it is small) to have less "diversity" than the total population did before isn't wrong it is just a stupid red herring in the discussion and utterly meaningless.

NO it is NOT! The biological definition of micro and macro was around long before creationists tried to pick it up.In the beginning they agreed with the biological definition. When it was shown the speciation (and even higher levels) events occur they have tried to change the definition.If you want to use defined biological terms then you will have to stick to the biological definitions. If you don't like what they mean then invent new words. There may be no need but it is there. Complex organisms (animals) like we are discussing don't reproduce without mutations in there. At the speciation level it may or may not be that mutations have an immediate effect.However, once speciation has occured it is a new ball game. You now have to separated populations that may well be (in fact are almost certainly) subject to slightly different selective pressures. In addition, there are verly likely going to be mutations that occur in one population but not the other. In fact so likely that it is close enough to guarenteed.Now you have two populations whose genetic changes AND selective pressures are different. Over time they diverge. Over time they may each undergo further speciation events themselves. Over time those populations diverge. Now you have macroevolution no matter WHAT level you want to put it at.Does this actually occur? Look at the genetics of various branches of the taxonomic tree. The genetics are just as the above scenario suggests they should be. The differences in genetics are ALL accountable for by the various mutation types we know occur. Of course you are. That is why you don't want mutations discussed and why you don't want to discuss what we would expect to see when we examine the genetics in detail. That is why you want to focus on the short term (and only occasional) case where one of the populations doesn't, by chance, pick up all the alleles of the orginal larger popultion. The blinkers you want to wear are not worn by others.Edited by NosyNed, : No reason given.

Crash, I have read about a mutation in some Italian village (IIRC) that conveys particular resistance to heart disease. It (IIRC again) is supposed to have appeared about 200 or 300 years ago. (Maybe they even have a name of the 'common ancestor'.However, since we don't have the genetic maps of the parents of that individual (and cohort) how do we know, other than assumption that it was a mutation?

No, maybe it was already in the gene pool but unexpressed. Maybe it was expressed but not noticed. (It wasn't until the last decade or less).How do we know?

How many gennomes do we have? Is this 'mutation' dominant? Do we know how many ppl are so resistant?

Thank you Crash. That seems to be very convincing indeed. I'll have to go back upthread and see what Faith has to say? (la-la-la --I'm not hearing you probably)

This is not a very reasonable explanation when it is in descendents of this one person but I'm not sure how to do the math to be sure of that.I'd like to see exactly what the difference in the gene is too.If we could see that we could know that it is a difference that can arise through mutation (though I'm not away of any difference that can not).I'd also like to see more samplings of other populations. Though it could have arisen independently we'd see the same pattern of individuals with it descended from one person.This is EXACTLY the pattern you'd expect from a reasonably new mutation. It doesn't fit into your ideas at all.

The fact that this kind of change CAN be caused by mutations is just ONE of the reasons for thinking it is. We know that mutations can produce a change of this type.You're suggesting that the mutation removed it rather than the other way around.So you're saying that billions of individuals have LOST a beneficial allele but the decendents of one person somehow kept it from previously?

Faith did point out that there may be very little selection on this allele since it might not affect anyone until after reproductive age.

I'd be surprised if many people of any sort are tested even partially. Do you have anything to back this up?

I know it is fascinating to see such ideas but this should be taken to a separate thread.Try a title like "Disobedience as a Mutatgen". That will be a nice eye catching title.

I think we can afford a short diversion to explain this term (even if Crash thinks it is utterly obvious).Going back to Darwin's "Origin of Species" we find him saying that life's diversity arose from "one or a few".He was saying that all of the wide diversity of life can arise from only a small number of earlier forms through the evolutionary process.The question then becomes: "Is it a few or one?"That is does all life have one form as the "common ancestor" way back there or are there several lineages with several starting points?How would you settle this? You'd have to both look at what the fossil record tells us and what life forms alive today are like.Obviously, if you pick a restricted group you find that there is lots of good evidence that all members of it arose from a very narrow base.Let's look at the mammals. The exhibt a set of characteristics that are most easily explained by accepting that they came from a single branch. This is from both the body form we see and, very strongly, from the shared genetics.From the fossil record we see that this common ancestor would have been about 200 some odd million years ago. The genetics happens (surprise!) to agree with such a date.We also see that all mammals share some deep biochemistry and genetics for which there is no good reason that we should think they all arose independently (especially with the fossil evidence pointing the same way).From this we conclude that not only could mammals share a common ancestor based on evolutionary processes but that they, in fact, do.It gets trickier and more complex to be sure that this can be extended further and further but so far it looks like the "few" is actually "one".This is not to say that life didn't arise more than once. It does suggest, though, that either only one branch made it through or the descendants of the other branchs are as yet unfound or unrecongnized or that there was an interchange of chemistry between the separate branchs to merge them into an apparent single one very, very early on. (by early I mean sometime before 3 billion years ago).

So, Faith, how many alleles for each locus did the human race have at the time of the flood? When was that?What is the average number of alleles for a locus now? If it is now smaller than it was when did the reduction occur?