Not Lamarck Again

first_imgRemember Lamarck?  He was the pre-Darwin evolutionist whose theories we were all taught were overthrown by Darwin’s superior theory of natural selection.  Lamarck’s theory of “inheritance of acquired characteristics” was shown to be demonstrably false by the dramatic experiments of Weismann, right?  It was never really so clear-cut as that, as evolutionary historians know, but that’s been the common understanding.  This week, Nature printed an “Insight Perspectives” article about epigenetics (“above genetics”) that, while not referring to Lamarck by name, discussed “acquired” traits that could be inherited by “non-Mendelian” methods.  Its author, Arturas Petronis,1 even spoke of the growing realization of the importance of epigenetics as a new “unifying principle” and a “paradigm shift” in the style of Thomas Kuhn.    For a long time since the structure of DNA was elucidated, the “central dogma” of genetics has been that DNA is the master controller of inheritance.  Information flows from DNA to proteins, and that dictates the phenotype (the outward form of the organism).  In recent decades, the effects of environmental factors onto the genome has become a growing area of research.  Proteins are able to “tag” the histone proteins onto which genes are wound, affecting which genes are expressed or repressed.  Some of these epigenetic tags can be inherited.  Like most dogmas, the central dogma has been an impediment to new ways of scientific thinking, Petronis claims:The nature-versus-nurture debate was one of the most important themes of biomedical science in the twentieth century.  Researchers resolved it by conceding that both factors have a crucial role and that phenotypes result from the actions and interactions of both, which often change over time.  Most ‘normal’ phenotypes and disease phenotypes show some degree of heritability, a finding that formed the basis for a series of molecular studies of genes and their DNA sequences.  In parallel to such genetic strategies, thousands of epidemiological studies have been carried out to identify environmental factors that contribute to phenotypes.  In this article, I consider complex, non-Mendelian, traits and diseases, and review the complexities of investigating their aetiology by using traditional – epidemiological and genetic – approaches.  I then offer an epigenetic interpretation that cuts through several of the Gordian knots that are impeding progress in these aetiological studies.It has been very difficult to assign cause-and-effect relationships from environmental factors to traits.  “Even strong associations between an environmental factor and a disease do not necessarily prove that the environmental factor has caused the disease,” he said.  It is even harder to establish environmental factors to inherited traits, he continued.  Even a term like heritability can be hard to nail down when talking specifics.  Multiple genes become involved, and statistical likelihoods.  Nevertheless, traits do become established in populations.  For instance, an article on Live Science shows that Tibetans have inherited a trait for hemoglobin that allows them to survive at high altitude.  Petronis asks for breaking the gene-centric paradigm: “I argue that taking an epigenetic perspective allows a different interpretation of the irregularities, complexities and controversies of traditional environmental and genetic studies.”    He gave some examples of how acquired traits and environmental effects can influence epigenetic tags that are heritable.  There is no longer a clear black-and-white distinction between the views of Darwin and Lamarck (neither of whom were mentioned in Petronis’s essay); the situation is now much more complex:In the domain of epigenetics, the line between ‘inherited’ and ‘acquired’ is fuzzy.  Stable epigenetic ‘nature’ merges fluidly with plastic epigenetic ‘nurture’.  The ratio between inherited and acquired epigenetic influences can vary considerably depending on species, tissue, age, sex, environmental exposure and stochastic epigenetic events, all of which are consistent with empirical observations that heritability is dynamic and not static.  Another close link between heritable factors and environmental factors in epigenetic regulation is the observation that exposure to certain environments has effects that, in some cases, are transmitted epigenetically for several generations.In his conclusion, he said that this new perspective has all the trappings of what Thomas Kuhn called a paradigm shift: “handling the same bundle of data as before, but placing them in a new system of relations with one another by giving them a different framework.”  It might explain things like sexual dimorphism, parental origin effects, remissions and relapses, intergenerational disease instances, decline of symptoms with age, and other things – questions that an old paradigm would not find interesting, but a new one would.  “The considerable theoretical and experimental potential of an epigenetic perspective makes it a strong alternative to the existing research into complex, non-Mendelian, genetics and biology.” he said.  “Although the existence of competing theories may create some discomfort, it can also catalyse discoveries and is indicative of a mature scientific field.”  Human genetics is not a closed book.    Oh, and what would this new paradigm mean for evolutionary theory?  Glad you asked.  Of all things, Petronis recalled an old quote by Hugo de Vries sometimes paraded with glee by creationists.  But by recalling this quote, he left the reader hanging.  In the new paradigm, what is the explanation for the arrival of the fittest? All of the ideas that I have discussed here are highly relevant to the understanding of the fundamental principles of evolution.  ‘Soft’, epigenetic, inheritance can have a key role in adaptation to environmental changes and can endure for more than a generation.  Phenotypic plasticity might stem mainly from the ability of epigenetic genotype (or epigenotype) – rather than genotype – to produce different phenotypes in different environments.  Heritable epigenetic variation could explain the faster-than-expected adaptation to environmental change that is often observed in natural populations.  In addition, the large intra-individual epigenetic variation in the germ line may shed new light on the problem presented by one of the first geneticists, Hugo De Vries, more than a century ago, in his book Species and Varieties: Their Origin by Mutation, when he wrote “Natural selection may explain the survival of the fittest, but it cannot explain the arrival of the fittest.”Petronis had nothing further to say about fitness or its arrival.  Furthermore, despite the title of his paper, “Epigenetics as a unifying principle in the aetiology of complex traits and diseases,” he gave no description of how any specific complex trait might arise by genetics, by epigenetics, or by any combination of the two.  He only said that a new paradigm shift might “shed light” on the problem presented by Hugo De Vries a century ago.1.  Arturas Petronis, “Epigenetics as a unifying principle in the aetiology of complex traits and diseases,” Nature 465, pp 721-727, 10 June 2010, doi:10.1038/nature09230.That Nature would let in the ghost of Lamarck is a sign of their desperation with Darwin.  So here we are a century after Hugo, waiting for some light.  Petronis doesn’t have any.  Hugo didn’t have any.  Darwin didn’t have any.  Lamarck didn’t have any.  We’ve been sitting in the dark an awful long time listening to this crowd promise that some day somebody will “shed light on evolution.”  Would you spare a dime for their paradigm?  Don’t buy their promissory notes; not even your great-great-grandkids can expect to collect.(Visited 19 times, 1 visits today)FacebookTwitterPinterestSave分享0last_img

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