Darwinism Epigenetics News

Darwin’s world sticks its toe in epigenetics

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And hopes that it’s just Darwin’s same old world.

In “Epigenetic Inheritance: What News for Evolution?” (Current Biology Vol 22 No 2 R54, DOI: 10.1016/j.cub.2011.11.054) by Ben Hunter, Jesse D. Hollister,and Kirsten Bomblies, we read,

What does spontaneous variation imply for the potential for epigenetic change to play an important role in evolution? First, consider the genome-wide variation in stability of methylation states. Among the variable sites identified in these A. thaliana genome scans, a large proportion changed state in multiple independent lines, suggesting that some sites are indeed ‘hotspots’ for epigenetic change [9,10], and rates of reversion are appreciable [10]. It has been known for some time that epialleles at some loci are ‘metastable’ and can change dramatically over generations [15]. Such instability suggests it is unlikely that alternative epialleles can contribute appreciably to stable evolutionary change [4].

While instability speaks against the idea that individual epialleles would contribute to long-term adaptive evolution, it does beg the question why there is variation among loci in epigenetic stability in the first place. As Richards has pointed out, one possibility is that the unstable epialleles are really just phenotypically inconsequential ‘‘genomic clutter’’ that is reset with passing generations [3].

Genomic clutter? Whoops! Sounds like “unstable epialleles” are competing with transposable elements to be the new junk DNA. Better not go there ….

On the other hand, such variation could also be part of a plastic environmental response system or, if selection can stabilize epigenetic states, then it becomes a standing supply of potentially heritable, adaptive epialleles [3]. A particularly intriguing possible explanation when considering the role that epigenetic variation may play in long-term evolution is that it is the propensity to vary, rather than any particular allelic state, that is under selection. Simulations have shown that phenotypic variation and plasticity generated by epigenetic instability can be beneficial in variable environments, and thus instability may itself be a target of selection.

Darwin’s natural selection is beginning to sound more and more like an ancient Greek god who didn’t create the world, but decides intelligently where he will intervene in it.

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