Epigenetic mechanisms which involve biochemical alterations to DNA structure have been documented to result in heritable changes in gene expression. Unlike mutations, however, epigenetic changes do not involve changes in the primary DNA sequence, such that a nucleotide would change into a different nucleotide. Nevertheless, the field of epigenetics has been a fertile ground for neo-Lamarckian ideas that implicate epigenetic mechanisms in the emergence of evolutionary novelty and thus aim to challenge the status quo represented by the neo-Darwinian frame, which emphasizes chance and randomness as the begetters of variation onto which natural selection acts.
This hypothetical form of inheritance, chiefly resurrected by semi-Lamarckian thought, hinges upon the idea that the hereditary material is influenced by environment or experience, in that the functional history of a gene spans a trans-generational effect. However, I cannot help but notice that this so-called independent inheritance system appears to have been quite exaggeratedly overstated, in rather a keen Kuhnian fashion, by those who wallow in the very notion of scientific revolutions. There has been no evidence documenting transgenerational epigenetics as an important driver of evolutionary change. In fact, there has been a lot of evidence indicating otherwise.
Examples of epigenetic mechanisms include processes such as DNA methylation, histone modifications, remodeling of chromatin architecture, and generation of non-coding RNAs. All of these processes lead to patterns of altered gene expression profiles. It is disconcerting that the neo-Lamarckians do not stress much the fact that these are all processes which are genetically-driven and under the influence of genes that are coded for by DNA nucleotides in the first place. For instance, the attachment of methyl, acetyl, or phosphate groups to the histone tails of nucleosomes requires the activity of certain enzymes that are also guided by transcription factors. Indeed, the expression of these transcription factors depends not only on the epigenetic code but also, quite importantly, on the DNA code as well. So, even if the neo-Lamarckians want to pit epigenetics against the modern evolutionary synthesis, their argument would be an oxymoron because the intergenerational effects themselves are under the control of genes.
The neo-Lamarckian argument also falls apart because the so-called intergenerational effects have been shown to be quite transient and do not progress beyond a few generations. The epigenome is effectively reset during the reprogramming events of the early stages of gametogenesis and embryogenesis. The few parent-specific imprint-marked genes which escape this reprogramming process are still also erased in the offspring’s germ cells and then re-established depending on the sex of the offspring. This is coupled with the added complication of the early segregation of the somatic and germ cell lines which would make the possibility of experience-driven changes in the somatic cells being passed on to the germ line quite a conundrum. Together, these notions paint a very bleak prospect of environmental modifications of DNA being passed on over many generations, as the neo-Lamarckians would have us believe.
It is also not entirely clear to what extent the environment can influence epigenetic changes or whether the constant resetting of epigenetic marks between generations makes “epigenetic inheritance” robustly adaptive over the long run. Further, this phenomenon of epigenetic inheritance has also not been very well documented in mammals, presumably owing to the extensive reprogramming events previously described.
The term “epigenetics” has been usurped by those with eager tendencies to embellish the process of evolution and break through the eventualities of the genetic code. The term has been bastardized beyond the conventional scope of what it is supposed to realistically refer to: regulatory mechanisms of gene expression and has, unfortunately, given rise to a false pop culture idea of a Lamarckian revival.