Transgenerational Epigenetics
<p>In plants, nematodes and fruit flies, transgenerational epigenetic inheritance is well documented. It has been argued that this form of inheritance may permit a population to adapt to fluctuating environments. The question is whether this is also true for mammals and, particularly, humans. Almost all of the experimental mouse models and the few observations in humans concern deleterious traits (congenital malformations, anxiety, glucose intolerance, obesity, cardiovascular diseases, cancer and premature death); an exception appears to be hepatic wound healing. This may, at least in part, be due to reporting bias, as negative effects are easier to spot than positive effects, but overall casts doubt on an adaptive role of transgenerational epigenetic inheritance in these cases.</p>
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<b>Roadmap to proving transgenerational epigenetic inheritance</b>
- Rule out genetic, ecological and cultural inheritance. For studies in mice and rats, inbred strains and strictly controlled environments need to be used.</p>
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- Identify the responsible epigenetic factor in the germ cells.</p>
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- Demonstrate that the epigenetic factor in the germ cells is responsible for the phenotypic effect in the next generation. If possible, remove the factor from the affected germ cells and demonstrate that the effect is lost. Add the factor to control germ cells and demonstrate that the effect is gained.</p>
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In conclusion, in my opinion, even if the molecular mechanisms exist to transmit epigenetic information across generations in humans, it is very likely that the transgenerational transmission of culture by communication, imitation, teaching and learning surpasses the effects of epigenetic inheritance and our ability to detect this phenomenon. Cultural inheritance has certainly had an adaptive role in the evolution of our species, but the evidence for transgenerational epigenetic inheritance, as laid out above, is not (yet) conclusive. For now, I remain skeptical. All this from article TE-- critical view</p>
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<img src="/5759982b-91a2-53f0-b25d-cfa7b971b083.png"/></p>
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In conclusion, in plants and in some animals such as nematodes, transgenerational epigenetic inheritance is well-documented and relatively common. Epialleles may even form the basis of some complex traits in plants, where epigenetic inheritance is usually, if not always associated with transposable elements, viruses or transgenes and may be a by-product of aggressive germ line defense strategies. In mammals epialleles can also be found, but are extremely rare, presumably due to robust germ-line reprogramming. How epialleles arise in nature is still an open question but environmentally induced epigenetic changes are rarely transgenerationally inherited, let alone adaptive, even in plants. Thus, although much attention has been drawn to the potential implications of transgenerational inheritance for human health, so far there is little support. On the other hand, the human transmission of culture and improved habits is clearly Lamarckian. To quote SJ Gould (The Panda's thumb, 1980) “Human cultural evolution, in strong opposition to our biological history, is Lamarckian in character. What we learn in one generation, we transmit directly by teaching and writing.” In this and other respects, perhaps it is premature to compare humans to plants (as Burbank did) in terms of their capacity to recall past environments, in this generation and the next.</p>
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<b>Transgenerational epigenetic inheritance</b> is the transmission of information from one generation of an organism to the next (i.e., parent–child transmission) that affects the traits of offspring without alteration of the primary structure of DNA (i.e., the sequence of nucleotides)—in other words, epigenetically. The less precise term "epigenetic inheritance" may be used to describe both cell–cell and organism–organism information transfer. Although these two levels of epigenetic inheritance are equivalent in unicellular organisms, they may have distinct mechanisms and evolutionary distinctions in multicellular organisms.
For some epigenetically influenced traits, the epigenetic marks can be induced by the environment and some marks are heritable, leading some to view epigenetics as a relaxation of the rejection of the inheritance of acquired characteristics (Lamarckism).</p>