Epigenetics: Maybe not that big of a deal, after all, says study

A new paper is arguing that epigenetic variation—basically, what happens when an environmental trigger turns genes on and off, or makes them express differently—may not survive over many generations and, thus, would not have much of an impact on evolution in general. Expect a lot of dissent. This will be an interesting debate and I'm looking forward to seeing how the evidence shakes out over a few more papers.



  1. my understanding of epigenetic changes is that they are reactions
    to a local environment and wouldn’t be expected to persist as the
    environment changed; That they are a mechanism for a population
    to temporarily optimise for a local environment over a time scale
    faster than DNA/protein mutation. But the science daily article seems to
    suggest that the conventional opinion is/was that epigentic changes are
    broadly persistent, is that really the case? Is there really such a consensus at this point?
    Am I so out of touch with biology?

  2. A classic ‘yesbut’.  As the methylation state is influencing local gene transcription, the methylation state of the current generation can have a very strong influence on the reproductive capability of that individual plant, and so even a short-lived transient change can exert a strong selective pressure.  Selection also isn’t affecting just that epigenetic change, but is occurring at the whole-genome level. Finally, it really matters what genes the modifications are influencing – even a transient shutdown for a few generations of a major DNA repair enzyme can lead to massive mutations at the DNA level, which will certainly have a significant effect on the long-term evolution of that plant’s descendants.  

  3. She’s arguing that the epigenetic changes themselves won’t persist, and not the epigenetic mechanism, right?

    Is there a reasonable consensus that the epigenetic mechanism(s) is the result of evolutionary selection? It seems reasonable to think that the ability to turn genes on and off in response to environmental changes is a very useful adaptation for a species, and would be selected for.

  4. How could epigenetic mechanisms undermine evolution any more than having a complex nervous system does?

    A nervous system with the capacity to develop new behaviors over time in response to environmental conditions is not considered a problem at all. How could a much more simple thing like a switch that turns off a gene in response to an environmental condition be a problem? Seems such a switch would be a nifty thing that would itself be subject to natural selection.

    1. The difference between epigenetics and a complex nervous system is that the epigenetic changes can be inherited.

      So the classic study of (I think) Scandinavian farmers who experienced a famine having “genetically” heavier grandchildren. Or verious epigenetic differences in the grandchildren of smokers vs non-smokers.

      That fact that it can be inherited makes it very different, although this paper seems to be arguing that it doesn’t make a big difference in the long term.

  5. Maggie, you’re mistaken about what epigenetic variation is. It’s not “what happens when an environmental trigger turns genes on and off, or makes them express differently”.

    Epigenetic variation consists of differences (among people) in the occurrence of chemical groups (e.g. methylation) attached to DNA, rather than differences in DNA sequence.

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