tag:blogger.com,1999:blog-1812431336777691886.post2308183417855213172..comments2024-02-29T03:57:00.088-05:00Comments on The Mermaid's Tale: Epigenetics and adaptive evolution: which wins?Anne Buchananhttp://www.blogger.com/profile/09212151396672651221noreply@blogger.comBlogger6125tag:blogger.com,1999:blog-1812431336777691886.post-44244947864926856342014-06-25T12:42:53.153-04:002014-06-25T12:42:53.153-04:00Thanks.Thanks.Anne Buchananhttps://www.blogger.com/profile/09212151396672651221noreply@blogger.comtag:blogger.com,1999:blog-1812431336777691886.post-12927225371928003992014-06-25T12:17:06.113-04:002014-06-25T12:17:06.113-04:00I don't have full access to this article on &q...I don't have full access to this article on "Behavioral Inheritance", regarding the Pavlovian experiments, but you and/or your readers might be interested. It's from 1966. <br />http://link.springer.com/article/10.1007/BF03001081Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-1812431336777691886.post-14250858952763050872014-06-24T20:03:00.199-04:002014-06-24T20:03:00.199-04:00Interesting. I didn't know about the inherita...Interesting. I didn't know about the inheritance claim of Pavlov. I think the NG article actually mistakes what Lamarck said, in a way that also applies to Pavlov's fellow-Russian Trofim Lysenko. <br /><br />Even if conditioned traits were inherited, even if over a long number of generations or even permanently, it would be rather more like artificial selection vis-a-vis natural selection. For Lamarck, the striving to do something or other came from within the animal, and was not opposed from without, as by an experimenter.<br /><br />Of course, an experience-conditioned change of a sort compatible with, or helpful to, reproductive success (fitness) would not really violate Darwin too seriously if its success was do to natural competition. In that sense the conditioning would be a random mutation-like event for the individual who happened to be conditioned. If it happened it would just show that there are more ways to be molded by selection than we had thought.<br /><br />Now, what if there were 'a gene' that made organisms liable to be conditioned in this way? Would that challenge standard evolutionary paradigms? I think perhaps not in any fundamental way. We'd say that we were 'adapted for' response to environmental experience.<br /><br />One can debate where s/he would draw the Darwinian vs revolutionary line and I think it would mainly be semantic. The real issue is whether this sort of experience can systematically be directed into trait-specific change that gets into the germ line. If it were at all general, it could be called Lamarck-without-the-striving aspect. <br /><br />I personally think we cling too tightly to dogma rather than realizing that we may not know of all the ways organisms evolve. The key Darwinian fact, to me, was to show clearly that life is a descent tree from common ancestry. However what worked worked, and is here today, is a secondary question, so long as we don't get mystic about foresight and such things.Ken Weisshttps://www.blogger.com/profile/02049713123559138421noreply@blogger.comtag:blogger.com,1999:blog-1812431336777691886.post-11556694198623525962014-06-24T13:53:05.174-04:002014-06-24T13:53:05.174-04:00Thanks very much for this very informative comment...Thanks very much for this very informative comment! I think that instead of facing up to the complexity we know, at the many ways and levels you describe, we fall into our own categories of convenience (is that also a 'category mistake'?).<br /><br />Somehow, science does work through much of this when the causal situation is relatively simple or clear, or something of the sort. But we don't take seriously enough that this isn't the rule.Ken Weisshttps://www.blogger.com/profile/02049713123559138421noreply@blogger.comtag:blogger.com,1999:blog-1812431336777691886.post-37898163568267530562014-06-24T12:32:24.456-04:002014-06-24T12:32:24.456-04:00Thank you for the discussion on epigenetics – this...Thank you for the discussion on epigenetics – this is of course an overtly neglected topic in today’s biology curricula. Unfortunately, three distinct concepts are intermingled when a separation would have been more useful –at least pedagogically: (1) “Classical” Epigenetics proposed by WADDINGTON; (2) MOLECULAR Epigenetics, which refers to covalent modification of DNA and chromatin, notably methylation; and (3) Epigenetics in conjunction of TRANS-GENERATIONAL EFFECTS in which parental behaviors and environmental exposure are manifest in ensuing generations. Let me complement the thoughtful discussion in this blog on epigenetics by separating the various meanings of ‘epigenetics’.<br />Comprehending Waddington’s thinking, notably genetic assimilation, as well as the related Baldwin effect, requires a sophistication of biological thought that the reductionist molecular biologists who discovered DNA methylation in the 1970s simply did not have and thus, they superficially adopted (hijacked?) the term “epigenetics” to describe the molecular phenomenon of covalent changes to DNA that does not affect its sequence. (For fairness, the complex regulation of methylation/demethylation was discovered much later). From then on, modern biologists used epigenetics with the mental image of DNA methylation even if they sought to explain phenomena that belong to the class of Waddingtonian epigenetics. What a tragedy! With the discovery of transgenerational effects in higher organisms (3) it was then obvious to invoke (2), DNA methylation, as an explanatory mechanism. <br />There is category mistake here: a biological phenomenon and a mechanisms that could, but does not necessarily explain the former, are mixed up. One of the most cogent analysis of this terminological problem is that by Ptashne (2007, Curr. Biol.) DNA methylation is just ONE part of a complex set of explanations for Waddington’s epigenetics. The central problem: DNA methylation is highly dynamic and reversible. It takes just few cell generations in culture to randomize the methylation status of gene loci. The solution lies in the biochemical circuitries that lock the gene activation state in particular configurations and require continuous extra-locus or even environmental inputs. Late but not too late in his life did Waddington realise that memory in transcriptional networks can provide the natural (non-proximate) explanation for his observations, as he told surviving participants of the famous meeting series on theoretical biology that he organized in the late 1960s at the Lake Cuomo in Italy. <br /><br />If DNA methylation is highly reversible, it is not much more different than, say, protein phosphorylation. So why all the fuss about DNA methylation? Why is not protein phosphorylation also ‘epigenetics’? DNA methylations have become all too convenient an “ersatz religion” for genetic reductionists when confronted with puzzling findings outside their mental framework. DNA methylation is then called “epimutation” - a diagnostic sign for the deep psychological need to perpetuate a familiar scheme of thought, namely, linear deterministic genetic reductionism. The reality is that DNA methylation is, like phosphorylation, but contrary to genetic mutations, a highly regulated process, integrated in a regulatory network. It is not the entry point to invoke randomness – the prima causa of everything.<br /><br />This is not to say that DNA methylation plays no role in genetic assimilation and transgenerational transmission of environmental exposure –but they are, much as mutations, only the proximate cause, and are so in a completely different way than mutations. True, DNA methylation controls the activation the genes –but who controls the controller?<br />S.H.https://www.blogger.com/profile/12601599991047544180noreply@blogger.comtag:blogger.com,1999:blog-1812431336777691886.post-9196646254003040562014-06-24T10:25:32.449-04:002014-06-24T10:25:32.449-04:00Thanks for these thoughts and for the tip about th...Thanks for these thoughts and for the tip about the review article.Holly Dunsworthhttps://www.blogger.com/profile/05260104967932801186noreply@blogger.com