How exactly could a traumatic experience change a person’s DNA?
Well this is something that we really only uncovered in the past ten to fifteen years through the study of epigenetics, which is basically the study of how environmental factors and experience can alter how genes are expressed without altering the underlying DNA sequence.
So it’s not the DNA code itself that’s being affected, it’s something else?
That’s right. We’re all born with our with our DNA and we used to think that wasn’t changeable and it’s not. But what we know now is that experience can make certain kinds of these DNA “tags”, which is the unscientific way to talk about it, that can tag onto our DNA. Those little tags can basically turn the gene on or off. And so while the same gene is still there, it could be not functioning or functioning differently and therefore the functional aspects and roles of that DNA are different.
So why would your body do this? What’s the evolutionary advantage?
I think it really depends on the situation. Just to give you an example, the research on the long term effects of the Holocaust might help explain this. We know those who experienced chronic stress, they tend to show lower levels of the stress hormone cortisol, which helps our body return to normal after trauma. Those who have things like post-traumatic stress disorder, they have these low levels of cortisol and so it’s not completely clear why this is the case in survivors. But Rachel Yehuda’s team recently found that these survivors seem to be making lower levels of an enzyme that breaks down this cortisol. So this could be considered to be an adaptation to keep more free cortisol in the bodies of these people who are being starved, which would allow their livers and kidneys to maximize their stores of glucose and all of these other things that would actually help them in response to prolonged starvation and other types of stress. But that same response is not going to be adaptive for the next generation who are trying to recover in a normal environment.