Part 2: Epigenetics And Evolution – Transgenerational Epigenetic Inheritance
New scientific findings involving epigenetics are having a profound impact on our understanding of evolutionary mechanisms. It is becoming increasingly apparent that epigenetic modifications play a critical role in the regulation of gene expression. In so doing, they produce phenotypic changes. It is becoming abundantly clear that these influences are an important factor in our own human experiences, influencing life span, mood disorders, immunological status, obesity or tendencies towards the variety of chronic illnesses that have afflicted our human experience. Although it has until recently been assumed that these epigenetic marks are cleared in each generation and then re-established by reiteration of similar environmental influences, it is now manifest that this is not always the case. The term ‘transgenerational epigenetic inheritance’ has been applied to this phenomenon.
Epigenetics is now an established discipline. Examples abound. For example, one of the first fully documented instances was the transgenerational epigenetic inheritance of flower symmetry from bilateral to radial in Linaria vulgari. This results from a change in DNA status, a process of methylation, rather from any change in the underlying DNA sequence. In essence, a different form of gene expression and its phenotypic trait correlates to either an active or silent state of underlying genetic code based on environmental experiences. This has been shown to be heritable over multiple generations and might be permanent. Obviously, there remain difficulties in ascertaining with certainty what might be an ‘epigenetic’ change and what could be an underlying genetic mutation, yet the concept seems robust. There is a means for the experiences of an organism within its environment to affect its genetic expression and that change can be either meiotically transferred to the next generation or through RNA transcripts in germ line cytoplasm to progeny. Importantly, in hologenomic evolutionary theory, the targets of these kinds of transfers and their influences are extensively available to organisms that are pictured as vast inter-related ecologies of innate and microbial cellular life… a microcosm within. We, and all hologenomes are subject to a vast array of both internal and external environmental influences in an exquisite, complicated and co-dependent interplay.