Legacies of trauma passed on through genes

I recently asked an audience what they knew about epigenetics during a discussion on emerging research on multigenerational legacies of traumas such as war, colonisation, famine and the possibilities for healing.

A young woman (who later introduced herself as Māori and mother of three) gave the definition along the lines of inheritance of environmental influences (received by the mother) to offspring.

“In my circle of mothers,” she told me during the break, “we talk about it a lot”.

The discussion was a Kōtuitui - interweaving conversations event organised by community support organisation Foundation North and its research arm, Centre for Social Impact. Speaking alongside a Pacific poet, a distinguished Māori community leader and professor of restorative justice, my role was to explain the science – and in particular the field of epigenetics.

Modern epigenetics emerged in the 1970s through thinking how, during development, a single genome (the complete set of genes that make up an organism) starting from a “blank slate” gives rise to the variety of different cell types. It was shown addition of a chemical (methyl) group to the gene promotor – the region of DNA that launches the gene transcription – can silence (or deactivate) that gene. Through the action of specialised enzymes, these patterns can be reinstated on new copies of DNA as the cell divides.

It was in the 1980s that the notion of epigenetic changes passing across generations was first explored in relation to the phenomenon of “imprinting”. “Imprinted” genes are those whose expression (activity) depends on their parent of origin. Although rare, “imprinted” genes indicated that the “blank slate” was perhaps not quite as clean as thought, and that some information (alongside DNA) could be passed onto future generations.
 

Furthermore, they see epigenetics as vindication of their longstanding argument that poor outcomes of these groups—from higher mortality, to addiction and incarceration rates – are caused not by inherent, fixed genetic makeup (as some genetic arguments – ‘warrior gene’ comes to mind – would have us believe) but because of persistent biological traces of past trauma. In this sense, ‘race’ and ‘ethnicity’ may not be genetic but are nonetheless biological; as the social experiences of living as a member of a certain group may change our biology in profound ways.

Some scientists have been critical of the enthusiastic public reception of human transgenerational inheritance, pointing out that while environment during formation of sex cells (in both parents) and during pregnancy can change epigenetic marks not only in the developing embryo, but also in sex cells of that embryo – thus passing the effects to the grandchild – there is no evidence of epigenetic changes further down the line: what happened to our great-grandfathers does not matter.

Yet this view sees heredity in a narrow way, modelled on the way DNA is transferred across generations. An increasingly influential view is that, when thinking of “heredity”, we must take into account all layers: genetic, epigenetic, behavioural and cultural as they all influence our phenotype (our characteristics as an individual), and the phenotype of future generations. Epigenetic changes that confer poor outcomes need not be transferred directly to the next generation: they could also be recreated, in every generation, if the conditions that created them persist.

It has also been noted that the epigenetic view is not necessarily better and fairer. Bodies marked by longstanding, heritable traces of trauma could be seen equally “unworthy” as bodies carrying “bad genes”. There is also a worry that rather than fixing the societal conditions that engendered these epigenetic changes, science and medicine could focus on developing epigenetic drugs that could simply switch genes on or off. These warnings show that epigenetic science cannot fix social injustice on its own: rather, a just and equitable society is a precondition for the right application of science.