Yet another journalist seems to have fallen for the epigenetics mavens: those revisionists who think that a form of Lamarckian inheritance can be important in evolution. These people claim that the environment itself directly changes the DNA, not by altering the sequences of bases, but by somehow placing methyl groups on some of the DNA bases (“methylation”). Such changes can be passed on to the next generation, and so the revisionists (aka “careerists”) argue that the inherited epigenetic changes could be subject to natural selection, leading to a form of evolutionary change that is, roughly, the inheritance of acquired characters.
In a new piece on Big Think,”How about a new theory of evolution with less natural selection?“, journalist Robby Berman pushes this idea, noting that it was a big part of the recent Royal Society conference on “New Trends in Evolutionary Biology: Biological, Philosophical, and Social Science Perspectives.” (I discussed the problems with this conference’s proposals here.)
Among the problems with seeing environmentally acquired epigenetic changes as an important cause of adaptation—problems that I’ve discussed ad nauseam—are the following:
- Virtually all epigenetic markers are wiped clean as the DNA goes through gamete formation, and wiped clean within a few generations after they arise. Such changes cannot serve as a basis for permanentadaptation, which is what the epigenetics mavens claim.
- There is little evidence for environmentally induced epigenetic changes in vertebrates, an observation relevant to the article under discussion.
- When geneticists are able to map adaptive changes in the genome using crosses and DNA sequencing, they invariably show changes in the base sequence of DNA, not to methylation of those bases.
- If some DNA base sequences are more liable to environmentally-induced methylation themselves, and those methylated changes are adaptive, then the susceptible DNA base sequences will increase in frequency. But this is straight natural selection on the DNA, not a drastic revision of how natural selection works.
Some methylation changes are coded by the DNA: DNA bases that say to the genome “put methyl groups on bases X, Y, and Z”, and that form of methylation can be adaptive, for example in mediating parent-offspring conflict. But this form of evolution is not not induced by the environment; rather, it’s coded in the genome itself, and evolves via conventional natural selection (i.e., mutations that change the DNA sequence in an adaptive way become more frequent.)