tag:blogger.com,1999:blog-37148773.post4496436579570818847..comments2024-03-27T14:50:47.345-04:00Comments on <center>Sandwalk</center>: The Mutationism Myth, IV: Mendelian HeterodoxiesLarry Moranhttp://www.blogger.com/profile/05756598746605455848noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-37148773.post-36531840527011069442010-06-06T01:02:48.013-04:002010-06-06T01:02:48.013-04:00Marcello--
In regard to your first point, certain...Marcello--<br /><br />In regard to your first point, certainly the views of individual Mendelians changed over time. Morgan's and Shull's views shifted noticeably in their books. The views of the later Shull are no less Darwinian than those of the early Dobzhansky. I'm not familiar with Sturtevant's views (though his history of genetics is available online, so it should be easy to figure out). <br /><br />I'm not sure that I understand your second point. The separation of heredity into 1) transmission genetics (parental genotype to offspring genotype) from 2) developmental genetics (genotype to phenotype) is a 20th-century innovation from Morgan's group. <br /><br />In the 19th century, "heredity" meant getting from <b>parent phenotype to offspring phenotype</b>. Today, we think of "heredity" as an issue of transmission genetics, and indeed, "genetics" now means "transmission genetics". <br /><br />A century ago, when mutations were known by their phenotypes and we didn't know about DNA or genes or chromosomes, a change in phenotype was part of the "mutation" phenomenon. <br /><br />Eventually we cut off the "altered development" part of the concept of "mutation-and-altered-development" and "mutation" was re-aligned as a process in transmission genetics. The developmental-genetic aspect of mutation got lost. <br /><br />This is part of the story of how development got left out of the Modern Synthesis. It wasn't deliberately cut, its just that the Modern Synthesis did not leave any room for the significance of "mutation-and-altered-development". <br /><br />ArlinArlinhttps://www.blogger.com/profile/03243864308260498878noreply@blogger.comtag:blogger.com,1999:blog-37148773.post-44131878759959768692010-06-05T23:46:32.840-04:002010-06-05T23:46:32.840-04:00Arlin,
I don't have access to the sources, but...Arlin,<br />I don't have access to the sources, but from what I could glimpse it seems that some geneticists started to cast doubts about the importance of mutations in evolution before the Synthesis was fully formed. This impression comes especially from Sturtevant's 1937 Essays on evolution (in the first essay he talks about the effects of selection on mutation rates).<br /><br />My impression is that geneticists of the Morgan school and "Darwinians" converged on an idea of mutation <b>without</b> altered development. This idea, experimentally supported, facilitated the construction and ridiculization of the mutationism myth, and provided a further motive for dismissing Bateson (for his opposition to Morgan's theory of inheritance).<br /><br />P.S. After reading your posts I have changed my previous ideas about Bateson (thank you!). Are you familiar with S. Newman's sort-of defence of Bateson's vibratory theory (in Laubichler and Maienschein anthology From embryology to evo-devo)?Marcello Pucciarellihttps://www.blogger.com/profile/00200354980868168566noreply@blogger.comtag:blogger.com,1999:blog-37148773.post-66185777085082751112010-06-04T17:37:59.546-04:002010-06-04T17:37:59.546-04:00As an alternative to divine creation, Darwinism wa...As an alternative to divine creation, Darwinism was obliged to identify some materialistic process that would be "creative", and Darwinians typically insist that this process is "selection" and is NOT variation. We'll discuss this argument in a future post. <br /><br />In regard to mutation as a "force", no, you are not mistaken. The architects of the Modern Synthesis conceptualized mutation in two ways: as a mass-action "force" that shifts allele frequencies, and as the ultimate source of "raw materials". That is, they saw mutation both as an Aristotelean material cause (stuff, material), and as an Aristotelean efficient cause (agent, force). <br /><br />Haldane, Fisher, and Wright looked at mutation as a "force" that, if powerful enough, could cause "evolution", by which they meant an allele fixation or some other major shift in allele frequencies. From the mutation-selection balance equation, they concluded that, because mutation rates are so tiny, the opposing "force" of selection rules and mutation is not an effective evolutionary force. <br /><br />From this, Fisher argued that we could discard all non-Darwinian theories of evolution, including Mendelism. <br /><br />Fisher was wrong again. The main advantage of the "forces" view is also its Achilles heel, and this is its reliance on continuous shifts in frequency as the common currency of evolutionary causation. In physics, the common currency of causation is displacement of a particle: multiple forces can achieve this effect, and their effects can be combined multiply due to this common currency. In classical population genetics, selection, drift, and mutation are "forces" that can "shift frequencies". This is useful because it puts all the different "forces" on the same playing field. <br /><br />Unfortunately, at the same time, use of this common currency prevents the recognition of mutation as a source of allelic novelty. Mutation can introduce a new allele. We could call this a "shift in frequency from zero to 1/N", but thats not the kind of "shift" the founders meant, because its discrete, not continuous, and because its not a common currency of causation: selection and drift cannot do it. Only mutation can shift a frequency from zero to 1/N. <br /><br />That is why the "forces" paradigm is inadequate and fails to uncover theoretical truths that can be derived under more general conditions, such as the potential for mutation-biased adaptation.Arlinhttps://www.blogger.com/profile/03243864308260498878noreply@blogger.comtag:blogger.com,1999:blog-37148773.post-45150732069584623492010-06-04T09:26:39.474-04:002010-06-04T09:26:39.474-04:00I was under the impression that mutation was recog...I was under the impression that mutation was recognised as an evolutionary force by the founding fathers of the modern synthesis (at least by Wright and Haldane). Am I mistaken?<br /><br />Also, I don't quite understand the discussion whether mutation or selection is the "creative" force. One makes mistakes, and the other sieves. It's typically human to see something creative in that :-)<br /><br />I like you posts, by the way.Corneelhttps://www.blogger.com/profile/02884855837357720225noreply@blogger.com