"Macro" vs "Micro" genetic "kind" mechanism?

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Creationists do even better, Phillip Johnson in his collection of mistatements, out of context quotes, and outright lies otherwise known as the book Darwin on Trial, claims that species possess a genetic limit to variation. This is stated as a "fact" in his book yet no supporting evidence or reference to such a limit is given. This fictional limit is used to explain the barrier between micro and macro evolution.

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What Johnson and other anti-evolutionists are going on about, as best as I can determine, is the phenomenon known as 'genetic homeostasis'. What this means is that populations undergoing intense directional selection (as in agricultural breeding programs) will often stop responding to selection for the trait at a certain point, accompanied with reduced fitness.Anti-evolutionists often cite Drosophila work done by Mather and Harrison, where they selected for increased numbers of abdominal bristles, as an example of limits to natural selection (and by extension, macroevolution). At some point the number did not increase beyond 36, as I recall. Anti-evolutionists jump on this, crowing that there is a limit to variation beyond which natural selection cannot go.Well, in a certain, obvious sense, they are right, but the Mather and Harrison example is not an illustration of their thesis. I Michael Lerner, the geneticist who coined the term 'genetic homeostasis' noted that it was not that the reduced fitness was caused by the population running out of variation, but that the intense selection for one trait, common in breeding progranms, disrupted gene complexes that had co-evolved over a long period of time in nature, and the reduced fitness was the response to this disruption.KCThis message has been edited by KCdgw, 07-06-2004 10:10 AM

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Could you give me a reference for the genetic homeostasis work? I would like to read up on it.

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Lerner's book, Genetic Homeostasis, is available online: Genetic homeostasis: Core Historical Literature of AgricultureKC

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However, I did not realize that the creo crowd was basing their genetic "limit" on this...Johnson seems to argue that since with artificial selection, one does not change a dog into a horse dramatically they must be genetically limited though he provides no support for this (and ignores the fact that dog breeders are selecting for specific characteristics).

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They get much of this from Richard Milton's "Shattering the Myths of Darwinism":

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This is Darwin's central idea of evolution in a nutshell: bears can become whales, or whale-like, given enough time and enough natural selection. However Darwin withdrew this claim from the second and later editions of the book.

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Almost certainly this was because as an animal breeder he knew from first hand experience that no plant or animal breeder has ever succeeded in producing a new species by selective breeding. Primarily this is because of what Harvard's Ernst Mayr called "genetic homeostasis" -- the barrier beyond which selective breeding will not pass because of the onset of sterility or exhaustion of genetic variability.

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Of course, besides getting Lerner's name wrong (Milton gets HIS info from a botched quote in a terrible book that I can't remember right now), the concept of genetic homeostasis is misunderstood.From: No webpage found at provided URL: http://www.alternativescience.com/shattering-the-myths-of-darwinism-contents.htmEDIT: the bad book was Jeremy Rifkin's Algeny. If you get a copy of Stephen Jay Gould's An Urchin in a Rain Storm (I think that's the title), you will find Gould's review of the book very entertaining.KCThis message has been edited by KCdgw, 07-07-2004 10:33 AMThis message has been edited by KCdgw, 07-07-2004 10:42 AM

I couldn't make head nor tail of it either.KC

I still can't make head nor tail of it.KC

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KC supposedly quoting Richard Milton writes:

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"This is Darwin's central idea of evolution in a nutshell: bears can become whales, or whale-like, given enough time and enough natural selection. However Darwin withdrew this claim from the second and later editions of the book.

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Almost certainly this was because as an animal breeder he knew from first hand experience that no plant or animal breeder has ever succeeded in producing a new species by selective breeding. Primarily this is because of what Harvard's Ernst Mayr called "genetic homeostasis" -- the barrier beyond which selective breeding will not pass because of the onset of sterility or exhaustion of genetic variability."

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The above quoting is a butcher shop special. No page numbers or any of the ordinary standards to be found.

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I suppose, in this graceless age, it is unreasonable to expect one to actually read a post before insulting its author. Just call me old-fashioned. Had you actually bothered to read my post, you would have noticed I mentioned that the quotation of Milton was from his very own website, entitled, appropriately enough, ”Shattering the Myths of Darwinism’. I even gave the link, which, if you actually bother to check, has the exact quote I noted.Now, while I am pleased you have learned to cut-and-paste vast swaths of text, I have to insist on being unreasonable, and noting that Milton’s description of ”genetic homeostasis’ is incorrect on several levels. First of all, the term was coined by Berkeley geneticist I. Michael Lerner, and while Mayr was correct in noting that loss of fitness is common in intense breeding programs, Lerner pointed out it was due primarily to the breeding program’s disruption of coadapted gene complexes that had developed over long periods of time in the wild, prior to domestication-- not exhaustion of genetic variability.

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"Darwin was well aware of one central fact that dominated all animal and plant breeding experiments - then and now. No one has ever bred a new species artificially - and both plant and animal breeders have been trying for hundreds of years, as have scientists."

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I suggest you read the following to disabuse you of such hyperbole:Dobzhansky, T and O Pavlovsky (1971). Experimentally created incipient species of Drosophila. Nature 230: 289-292.KC

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Those who know the truth are not equal to those who love it-- Confucius

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So no genetic barrier to "macro" evolution has been shown.

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There is no barrier. It has never been described, nor demonstrated. The 'genetic homeostasis' gambit can only be played by completely distorting the term. It only applies to drastically intense selection, as seen in breeding programs. Most selection in nature, as any student of evolution knows, and which our friend Herpeton conveniently avoids discussing, is far less intense. Milton conveniently avoids Lerner when discussing genetic homeostasis, for good reason. On page 5 of his book, Genetic Homeostasis, Lerner writes (my emphasis):

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The three types of evidence which contribute most heavily to the theory advanced refer to:

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1. data on artificial selection in instances where deceleration of gains is observed or a plateau is reached without apparent reduction in genetic variability.

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Of course, Milton doesn't mention that, now does he? And Herpeton just accepted Milton's screed unquestioningly. So have a lot of creationists, who cite Milton's quote with relish.KCThis message has been edited by KCdgw, 10-28-2005 07:36 AM

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Those who know the truth are not equal to those who love it-- Confucius

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What they all have in common is that they are the source/origin of something. Genetic homeostasis is caused by Genesis being true.

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Considering your very poor grasp of just what genetic homeostasis is,
you have no business lecturing anybody about it.

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When you can falsify genetic homeostasis and the experimentation, and the fossil record, and correct your errors - let me know.

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Lerner falsified your ridiculous caricature of genetic homeostasis by pointing out that there was extensive evidence that contradicts it:

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The three types of evidence which contribute most heavily to the theory advanced refer to:

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1. data on artificial selection in instances where deceleration of gains is observed or a plateau is reached without apparent reduction in genetic variability.

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I understand you have a lot of internet ”street cred’ invested in your misconception of genetic homeostasis. However, clinging to such such a caricature of the actual concept after being shown the truth simply emphasizes to us that you really have no idea what you are talking about. It is finally time to face the fact that genetic homeostasis is not the result of what you say it is, but instead is a direct result of natural selection producing coadapted gene complexes which, when disrupted by intense artificial selection, result in lowered fitness of the population. Cut your losses and find something different to argue about, there’s a good chap.KC

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Those who know the truth are not equal to those who love it-- Confucius