Freethought & Rationalism Archive

pz · 06-12-2003, 09:26 PM

Quote:

Originally posted by The Lone Ranger
Weismann was the guy who cut the tails off several generations of mice, showing that acquired characters are apparently not passed on to offspring.

The so-called "Weismann barrier" is the notion that acquired characters cannot be passed on to offspring.

Sorta. The barrier refers specifically to the separation of germ and somatic lineages in development, and lack of any transformation of germ tissues to somatic and vice versa. It has the net effect of preventing inheritance of acquired characters, but it's also a more sweeping statement about the nature of metazoan development and organization.

He's famous as a cytologist (despite being half blind), and he arrived at his ideas about Weismann's Barrier from microscopic observations of cells and embryos, but he also did that sadistic experiment with mice. For 57 generations. You'd think somebody would compose a nursery rhyme about it or something.

lpetrich · 06-12-2003, 09:27 PM

Quote:

Originally posted by Nic Tamzek
*What* is it about acquired characters that is so appealing to that particular noncreationist but antiDarwinian fringe?

Beats me.

Maybe it's the simplicity of the concept. Maybe it's the idea that some of one's learning and experiences can be passed on to future generations.
Maybe it's an attraction to an idea that is perceived as heresy.

Lamarckism is a common bit of folklore, much older than Lamarck himself, whose main theory of evolution was a form of orthogenesis. One can find it in the Bible in Genesis 30, and one notices it in the perplexity that some people over the centuries have had about the non-inheritance of mutilations.

Back in the 1920's, Paul Kammerer, one of the last reputable biologists to advocate Lamarckism, wrote passionately how if acquired characteristics are not inherited, then each new generation would have to start from scratch. He even claimed to have evidence of its occurrence, evidence that other biologists had difficulty duplicating.

Evidence that turned out to be faked!

However, Lamarckism would last longer in the Soviet Union, as a result of the official favor that got granted to plant breeder and quack geneticist Trofim Lysenko. Official favor that included Joseph Stalin's belief in Lamarckism.

RufusAtticus · 06-12-2003, 09:49 PM

Quote:

Originally posted by lpetrich
To be precise, animal germ cells, like plant ones, are also produced from somatic cells, but in most species are produced very early in development and set aside.

Well as I see it, animal somatic cells are derived from germ cells.

lpetrich · 06-12-2003, 10:01 PM

Quote:

Originally posted by The Lone Ranger
Weismann was the guy who cut the tails off several generations of mice, showing that acquired characters are apparently not passed on to offspring.

That experiment is significant because it was done under controlled circumstances; Dr. Weismann insured that only amputated-tail mice were allowed to breed over the generations, and he carefully measured the length of the mice's tails.

But I've seen 19 and 22 as the number of generations he performed this experiment.

There are numerous "natural experiments" in mutilation, however. Plants often get heavily mutilated, yet they continue to grow as if nothing had happened. Simply consider what lawn grass does.

Some dogs have (or used to have) their (external) ears and tails cut off to make them look more plucky or whatever; however, their offspring are still born with ears and tails.

And various human societies practice various forms of mutilation, but the next generation always needs to have it done. Forms like tattoos, scarification, circumcision, base-of-penis incision, clitoridectomy, knocking out of teeth, etc.

Some Lamarckians make the counterargument that mutilations are not the acquired characteristics that get inherited, that it is internally-derived changes that get inherited. But there is no evidence of that kind of Lamarckism either; learning does NOT get inherited, as is apparent in adopted human children who are raised in a society very different from that of its parents.

lpetrich · 06-12-2003, 10:03 PM

Quote:

Originally posted by RufusAtticus
Well as I see it, animal somatic cells are derived from germ cells.

As are those of plants.

The cycle is

germ cells -> fertilized egg cells -> somatic cells -> germ cells

For most of the animal kingdom, the somatic phase is brief; germ cells are set aside in early embryonic development. However, plants do not have that set-aside mechanism.

RufusAtticus · 06-12-2003, 10:13 PM

Quote:

Originally posted by lpetrich
For most of the animal kingdom, the somatic phase is brief; germ cells are set aside in early embryonic development.

No, I think you have it wrong, for most of the animal kingdom, somatic cells are set aside in early embryonic development.

ps418 · 06-13-2003, 06:19 AM

Quote:

Originally posted by David Gould
Saw a program last night about Ted Steele and his work at trying to prove that inofrmation can cross the Weismann barrier. I am hoping that some knowledgable individuals here can give me some information on:

1.) Whether it is now accepted that the Weismann barrier can be crossed;

2.) The implications for evolutionary theory; and

3.) What are the problems with it.

Gert Korthof has an informative review of Steele's book:
Retrogenes: genes that don't behave.

Quote:

Steele's main scientific claim, roughly stated, is that an acquired property such as a specific immune response can be inherited (23). This is the most important and interesting claim of the book.

. . .

The main factual claim: genetic mutations involved in immune response can be inherited.
This claim implies that a parent incorporates a new DNA sequence specific for the infection, in his sex cells and transmits it to its progeny. In that way the next generation could respond immediate, specific and adequate to the same bacterial or viral infection. To prove the case it should be shown that a specific DNA sequence not present in the parent before the immune response, is present after the immune response in the parent's lymphocytes and sex cells and in the body and sex cells of the progeny. This experiment has been done with mice, but unfortunately the outcome is inconclusive. The experiment was done in the late 70s and in the twenty years after that nobody apparently succeeded in completing such an experiment. This is a pity, because it would have constituted the strongest possible direct evidence for the inheritance of acquired immunological characteristics. However Steele is preparing new experiments with genetically modified mice which will allow a definitive real-time demonstration of a soma-to-germline transport. Lamarck's Signature is mainly concerned with indirect evidence. Indirect evidence can be compelling, especially when no alternative explanation is available. Furthermore evidence in evolutionary research is almost always indirect. Fingerprints, footprints, signatures: it's all detective work.

. . .

What is his indirect evidence?

The diagram shows that there is a germline and a somatic configuration of the antibody genes. And this seems a unique and perfect opportunity to detect soma-to-germline feedback, because somatic configurations simply should not be present in the germline. The detective story starts with looking at genes in the germline and asking questions. Particularly looking at pseudogenes: non-functional copies of functional genes. They are non-functional because they cannot be transcribed. Of those a subclass, the processed or retro-pseudogenes, have a story to tell. These 'processed' pseudogenes are lacking introns. Introns are a common feature of normal genes. The question is: how did those 'processed' pseudogenes originate? Because of a lack of introns they are thought to have arisen by reverse transcription of mRNA, followed by insertion of DNA into the chromosome. Steele didn't discover these 'processed' pseudogenes. They are in the textbooks (14,15,16,17,18). However Steele interprets them as the final step of his soma-to-germline feedback mechanism. How does he know that they originate from the soma and not from the germline itself? Because the removal of introns implies transcription and transcription implies gene-expression and of course not all genes are expressed in germline cells. Tissue-specific genes are only expressed in somatic tissues. Orthodox neo-Darwinism can't explain expression of tissue-specific genes in germline cells, because they are not supposed to be expressed at all in germline cells. However, to evaluate Steele's evidence one needs more knowledge about retro-genes and gene expression in germline cells in general, than is given in the book. I need to know which genes are normally expressed in germ cells.

There is detailed indirect evidence in the book: the distribution of amino acid variability of germline chicken V-pseudogenes (2) (the so-called 'Wu-Kabat structures' (p176) (7); the recombination process itself: the so-called 'integration footprint' (p180). I don't have the expertise to evaluate this evidence, however I think it's safe to state that Steele showed that there could be a mechanism for the flow of information from somatic RNA to germline DNA (see figure above). Later I found that this mechanism is called retrofection and was described by Linial(1987) (18) and is common in mammals! So Steele's soma-to-germline feedback mechanism is partly based upon the well-known mechanism of retrofection. The feedback mechanism could be an example of the reverse flow of information through a 'tiny hole' in Weismann's Barrier.

Even if this reverse flow of information is confirmed, there is still another question unanswered. If this reverse flow of information results in pseudogenes, of what use are non-functional pseudogenes for the species? They need to be expressed to be useful. There is another question about usefulness. Feedback could make sense because there is a selection process involved: some lymphocytes die, others proliferate. However does it really make sense to store successful somatic configurations in germline DNA? It seems to be against the philosophy of the immune system: "to prepare for the unknown". It would only make sense to store information about immune responses in the genome if exactly the same type of bacterial or viral infection would reoccur in the next generation. Do they? HIV evolves about a million times faster than human genes (4). So the additional value of genetic feedback would not be great, I presume. Most of the time it would be outdated information (5), apart from the risk that random insertion of DNA into chromosomes may damage genes and result in cancer (22).

Patrick

ps418 · 06-13-2003, 06:22 AM

Another point Korthof makes that should be highlighted is that even if Steele's hypothesis is true, it is true for the immune system. It doesn't appear to be a general Lamarckian mechanism by any means.

Patrick

Kevin Dorner · 06-13-2003, 06:53 AM

Quote:

Originally posted by pz
For 57 generations. You'd think somebody would compose a nursery rhyme about it or something.

Even the mice have lamented
Weismann's lack of "foresight" was demented.
Far more male generations
Have had mutilations
Yet foreskins are not "circumvented."

Calzaer · 06-13-2003, 08:39 AM

Quote:

Maybe it's the idea that some of one's learning and experiences can be passed on to future generations.

Pardon my stupidity, but aren't "instincts" examples of learning and experience passed on to future generations?

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06-13-2003, 06:22 AM	#18
ps418 Veteran Member Join Date: Mar 2001 Location: Louisville, KY, USA Posts: 1,840	Another point Korthof makes that should be highlighted is that even if Steele's hypothesis is true, it is true for the immune system. It doesn't appear to be a general Lamarckian mechanism by any means. Patrick

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