About two weeks ago, the BBC’s “Future” website published a long science article touting the importance of epigenetic effects in humans: the idea that various behaviors, traumas, and psychological propensities produced by the environment on parents can be transmitted to their offspring. This is supposed to act in a “Lamarckian” way: the environment modifies the parents’ DNA or proteins by putting chemical markers on them, these modifications get passed on without any change in the genetic code. In other words, it’s the inheritance of an acquired character, something that is generally ruled out by the way genes work.
Click on the screenshot below to see the BBC’s breathless take:
The article gives several reports of the kind of stuff that’s inherited: health problems passed on to the sons of Civil War prisoners (but not their daughters), changes in the stress hormones in the offspring of Holocaust survivors, increase in the mortality of the grandsons of Swedish males who survived a famine and, in mice, increased sensitivity to a chemical odor in offspring and grand-offspring of mice who had learned to fear that odor by getting a shock when they smelled it. The BBC then touts all this as having big implications for humans:
But if these epigenetic changes acquired during life can indeed also be passed on to later generations, the implications would be huge. Your experiences during your lifetime – particularly traumatic ones – would have a very real impact on your family for generations to come. There are a growing number of studies that support the idea that the effects of trauma can reverberate down the generations through epigenetics.
. . .if humans inherit trauma in similar ways, the effect on our DNA could be undone using techniques like cognitive behavioural therapy.
“There’s a malleability to the system,” says Dias [Brian Dias, the author of the mouse study]. “The die is not cast. For the most part, we are not messed up as a human race, even though trauma abounds in our environment.”
At least in some cases, Dias says, healing the effects of trauma in our lifetimes can put a stop to it echoing further down the generations.
Well, we want to heal the effects of trauma in our lifetimes because trauma is painful, and none of these studies show any way to stop the supposed inheritance of trauma save by not exposing parents to trauma in the first place. In other words, the clinical implications of all this work is negligible.
But, as I’ve emphasized repeatedly, studies showing the “legacy of trauma” are more often than not flawed, relying on p-hacking, small sample sizes, and choosing covariates, like sex, until you get one that shows a significant effect. Further, there is no evidence for the inheritance of epigenetic effects in any organism beyond two or three generations, for epigenetic markers get reset, being wiped out during sperm and egg formation.
Finally, almost every study cited by the BBC report—save the Civil War study, which is too new to garner general acceptance— has been subject to criticism, criticism barely mentioned by the BBC. The mouse odor study by Dias and Ressler, for instance, was criticized in Genetics by Gregory Francis, who said that Dias and Ressler’s work was too successful:
The claim that olfactory conditioning could epigenetically transfer to offspring is based on successful findings from both the behavioral and neuroanatomical studies. If that claim was correct, if the effects were accurately estimated by the reported experiments, and if the experiments were run properly and reported fully, then the probability of every test in a set of experiments like these being successful is the product of all the probabilities in Table 1, which is 0.004. The estimated reproducibility of the reported results is so low that we should doubt the validity of the conclusions derived from the reported experiments.
Why was it “too successful”? Francis gives a number of reasons, which include unconscious manipulation of the data, poorly designed studies, and unreported experiments. Regardless, the mouse odorant experiments—and remember, even the effects reported lasted just two generations—should only be mentioned if you include Francis’s caveat. The BBC somehow overlooked that.
In humans, both the Swedish and Dutch famine studies, and the pitifully small sample in the Holocaust study (whose results have largely been disowned by the authors themselves) have been analyzed on a useful post by Kevin Mitchell, a neurogeneticist in Dublin, who rejects all the conclusions and winds up, after reviewing the corpus of highly touted human studies published through May of last year:
In my opinion, there is no convincing evidence showing transgenerational epigenetic inheritance in humans. But – for all the sociological reasons listed above – I don’t expect we’ll stop hearing about it any time soon.
Mitchell also has a useful take on why, given the methodological and statistical issues with the human “epigenetic” findings, they’re still accepted by journals and beloved by the media. The BBC is just one of many examples of the latter; Mitchell cites several breathlessly uncritical articles in the media about epigenetic inheritance in humans.
I’ll reproduce Mitchell’s analysis below about the misguided public love of epigenetic inheritance in humans, but bookmark his article if you want a useful guide to skepticism about such studies:
So, if these data are so terrible, why do these studies get published and cited in the scientific literature and hyped so much in the popular press? There are a few factors at work, which also apply in many other fields:
- The sociology of peer review. By definition, peer review is done by experts in “the field”. If you are an editor handling a paper on transgenerational epigenetic inheritance in humans (or animals), you’re likely to turn to someone else who has published on the topic to review it. But in this case all the experts in the field are committed to the idea that transgenerational epigenetic inheritance in mammals is a real thing, and are therefore unlikely to question the underlying premise in the process of their review. [To be fair, a similar situation pertains in most fields].
- Citation practices. Most people citing these studies have probably not read the primary papers or looked in detail at the data. They either just cite the headline claim or they recite someone else’s citation, and then others recite that citation, and so on. It shouldn’t be that way, but it is – people are lazy and trust that someone else has done the work to check whether the paper really shows what it claims to show. And that is how weak claims based on spurious findings somehow become established “facts”. Data become lore.
- The media love a sexy story. There’s no doubt that epigenetics is exciting. It challenges “dogma”, it’s got mavericks who buck the scientific establishment, it changes EVERYTHING about what we thought we knew about X, Y and Z, it’s even got your grandmother for goodness sake. This all makes great copy, even if it’s based on shaky science.
- Public appetite. The idea of epigenetic effects resonates strongly among many members of the general public. This is not just because it makes cute stories or is scientifically unexpected. I think it’s because it offers an escape from the spectre of genetic determinism – a spectre that has grown in power as we find more and more “genes for” more and more traits and disorders. Epigenetics seems to reassure (as the headline in TIME magazine put it) that DNA is not your destiny. That you – through the choices you make – can influence your own traits, and even influence those of your children and grandchildren. This is why people like Deepak Chopra have latched onto it, as part of an overall, spiritual idea of self-realisation.
That’s a good and thoughtful analysis.
So caveat lector, and, BBC, you really were derelict in publishing that article. You misled the public about the findings of these studies, as well as about their implications for clinical psychology.
I’ve put a test below where you can analyze what seems to be an error made by the BBC in its analysis.
A TEST FOR READERS
The BBC, in referring to the Civil War trauma that had effects on the offspring of prisoners, rules out one form of cultural transmission by saying this:
But what if this increased risk of death was due to a legacy of the father’s trauma that had nothing to do with DNA? What if traumatised fathers were more likely to abuse their children, leading to long-term health consequences, and sons bore the brunt of it more than daughters?
Once again, comparing the health of children within families helped rule this out. Children born to men before they became PoWs didn’t have a spike in mortality. But the sons of the same men after their PoW camp experience did.
As I interpret this (and I haven’t seen the study), the comparison doesn’t rule out the abuse hypothesis at all. Why not?