Comment 3 by Michael Austin :

I know that I've read in more than one of Dawkins' books (currently reading that exact passage in 'River out of Eden' ) that genes do not learn from behavior of their bodies. Has that been overturned now?

Yes and no. Not from the behavior of the body, but from certain common stresses on the cell that don't necessarily fall into the usual deadly ruleset of natural selection.

The way I understand it, epigenetic methylation can create a thick heterochromatin that renders a gene inaccessible to transcription factors so that it isn't expressed in the cell. The underlying DNA remains unchanged in a more classical sense, i.e. the gene is intact and in a state that would otherwise be active, yet it is masked, or 'silenced,' and this is clonally inherited.