This isn’t the first time we’ve encountered journalistic hype about epigenetics: last March there was a dire puff-piece in the Guardian asserting that epigenetics was the death knell of Darwinism. I went after it, arguing that while epigenetics was a novel and important new phenomenon in genetics and development, it wasn’t poised to completely revise our view of evolution for three reasons.
First, epigenetically inherited changes in DNA and protein, like methylated bits of DNA, ultimately rest on “normal” mutations in DNA that affect those changes. Things get methylated because the nucleotide bases in DNA code for that methylation. How can “nongenetic” changes in DNA reside in the DNA? Here’s one way. There are genes whose DNA sequence tells them to do this: “put methyl groups on another bit of DNA if you detect that you’re in the body of a male. Don’t do that if you’re in the body of a female.” Males and females would thus have the same DNA code, but it would be used differently depending on the DNA’s “environment”—for example, different hormone titers in males vs. females. The two sexes would then have produce different types of modified DNA even though their primary DNA sequences were identical. These modifications usually last only one generation, and then are reset when the DNA finds itself in a new body that could be of a different sex.
Second, as I just noted, in nearly all cases the epigenetic modifications are not inherited past one or two generations, so they can’t serve as lasting templates for evolutionary change. Insofar as those changes are important in evolution, they must ultimately reside in the primary nucleotide sequence of DNA, the genetic material.
Finally, those who tout the importance of epigenetics in evolution, most notably Eva Jablonka and Marion Lamb, keep trotting out the same handful of tired examples, like changes in toadflax and mouse coat color, that are inherited only temporarily and have nothing to do with evolution.More.