The Daily Beast distorts epigenetics with bogus claims that children can “inherit memories of the Holocaust”

I’ve written extensively on this site about recent claims that environmental modifications of DNA, through either methylation (sticking a -CH3 group onto DNA bases or by changing the histone scaffolding that supports the DNA, can constitute a basis for evolutionary change. This claim is simply wrong. To date, while we can show that environmental “shocks” given to animals or plants can sometimes be passed onto their descendants, the inheritance lasts at most three or four generations, then disappears. This cannot in principle support evolutionary change, which requires DNA changes that are permanent, so that they can spread through a population and effect a long-term genetic transformation.

Further, the changes shown are almost never “adaptive”—that is, they usually don’t produce anything that would enhance reproduction even under the environmental conditions in the lab that produce them.

Finally, extensive genetic mapping of real adaptations in nature, ranging from insecticide resistance in mosquitoes to lactose intolerance in humans and to armoring in marine stickleback fish, show that the changes invariably reside in the sequence of DNA bases themselves, not in add-on methylation or histone changes produced by the environment. I don’t know a single adaptation in nature that, when we isolate down its genetic basis, resides in some environmentally modified, epigentic change in DNA that can be transmitted for generations.

(Let me add here that epigenetic changes have promoted adaptive evolution when those changes reside in the DNA itself: that is, there are stretches of DNA that, in effect, tell the organism things like: “put a methyl group in the DNA on nucleotide X”. But these changes are themselves the product of conventional natural selection, and the epigenetic changes are produced by the DNA itself and not by the of the environment.)

Nevertheless, because the idea of evolution caused by environmental modification of our genomes is both appealing and “nonDarwinian”—violating how scientists think evolution works—it appeals to a subset of people who think that the theory of evolution is woefully incomplete. These are the “Kuhnabees” like Steve Gould, who think a brand new evolutionary paradigm is in order. (The Templeton Foundation gives out millions of bucks for people trying to reach this conclusion.)  I’ve been critical of this type of revisionist excitement, not because I want to defend the modern evolutionary synthesis at all costs, but for the reasons stated above: there’s no evidence for lasting environmentally-caused, adaptive modification of DNA, and genetic mapping experiments of real evolved adaptations invariably show that the evolutionary changes residing in the DNA’s sequence of nucleotide bases: the order of Gs, Cs, Ts, and As.

But the juggernaut rolls on, promoted by articles like this one in The Daily Beast by Elizabeth Rosner, “Can we inherit memories of the holocaust and other horrors?” (Subtitle: “In the trailblazing field of epigenetics, researchers are finding evidence that the descendants of victims of atrocities are inheriting those experiences in their DNA.”)

It’s the standard boilerplate article, showing some environmental modification of DNA that can be inherited for a few generations, but then bears a title and subtitle that are wholly misleading, and are echoed in the article’s text.

Rosner cites three experiments, only one of which I’ve been able to read. That one is a study of mice given an electric shock when exposed to a particular odor (reference and free access below). After a while, the mice froze in the presence of the odor (cherry blossoms), even in the absence of a shock. This is a pretty normal result. But then the authors bred subsequent generations of mice and showed that they, too, froze in the presence of that specific odor but not others. This behavior was associated with hypomethylation in sperm (reduced methylation) affecting a particular gene associated with olfaction. This genetic change was, in turn, associated with changes in brain structure. This is a correlation, not a causation, but it’s certainly intriguing.

But the inheritance of this behavior lasted only two generations: last seen in the grandchildren of the exposed mice. While author Rosner says the inheritance lasted “three subsequent generations” beyond the offspring of the tested mice—that is, a total of four generations of inheritance—I can see only two generations of inheritance. Unless I’m misreading, Rosner has misrepresented the results, and of course there is no testing a hundred generations later, which would be necessary if this freezing behavior (which is simply a neural response to shock, and not necessarily adaptive), were to be the basis of a real adaptation.

Now reacting to an odor behaviorally is not the same thing as remembering the Holocaust. Rosner gets that conclusion from a study of 32 Holocaust survivors (a small sample, with Rosner citing only a book and not the original papers). Apparently that study showed that PTSD in the offspring of PTSD-afflicted Holocaust survivors than in the population as a whole (again, I haven’t seen the data, and don’t know what the control group was, which should properly be the kids of non-PTSD Holocaust survivors). And I’m dubious when the study’s author, Rachel Yehuda, says she’s found this correlation “‘inexplicable’ by any other means than intergenerational transmission.”

Well, cultural transmission is also intergenerational (traumatized parents could treat their children in a way that these kids would themselves be traumatized), but let’s assume that the author of that study managed to show that the inheritance was truly genetic rather than cultural. (This kind of separation isn’t easy, and often uses adoption studies.)

And if the changes were genetic, were they due to methylation or to changes in histones? Nothing is said in the article. What Rosner and other summaries say is that Holocaust survivors have lower levels of cortisol, a hormone that helps people recover from trauma (clearly not an adaptive response), but also lower levels of an enzyme that breaks down cortisol, helping store metabolic energy—something that might be adaptive under starvation. Most important, the children of these survivors also had lower levels of cortisol—but (unlike their parents) also higher levels of the enzyme that breaks it down, an environmental modification of biochemistry that was inherited across one generation. Both of these modifications are palpably nonadaptive in the offspring, as reduced cortisol makes you recover more slowly from trauma, and so the offspring of Holocaust survivors would be more susceptible to trauma.

While you can make up a story why being more likely to get PTSD if your parents were traumatized might be adaptive, you have to do some tortuous argument here. I could, with a minute’s thought, make up an adaptive story were the results to be in the opposite direction. Further, you can easily argue that this is simply a biochemically induced change, heritable for just one generation, that doesn’t modify offspring in an adaptive way. Too, there’s no evidence to date that this change in behavior persists for more than one generation. I’d also like to see adoption or other studies showing that the correlation between parents and offspring is due to genetic rather than cultural inheritance. Finally, note that what we have here is “heritable” changes in mental illness, not heritable “memories of the Holocaust”, as the article’s title implies.

Finally, Rosner mentions a book that produces what I see as very slim evidence for heritable PTSD:

Psychiatrist Nirit Gradwohl Pisano published a book titled Granddaughters of the Holocaust: Never Forgetting What They Didn’t Experience. She focused on ten subjects who are survivors’ grandchildren and, following current theories in epigenetics, found evidence of what she refers to as the “hard-wired” PTSD passed down to the descendants of survivors.

“[These] ten women provided startling evidence for the embodiment of Holocaust residue in the ways they approached daily tasks of living and being … Frequently unspoken, unspeakable events are inevitably transmitted to, and imprinted upon, succeeding generations. Granddaughters continue to confront and heal the pain of a trauma they never experienced.”

Ten subjects! Yes, it’s two generations of inheritance, but did Pisano rule out, in her book, cultural transmission of propensity to PTSD? How did she know it was “hard-wired” (i.e., in the DNA)? Note, too, the bogus “unspoken, unspeakable events inevitably transmitted to. . . succeeding generations.” That is a gross distortion, and one that Rosner doesn’t even bother to examine critically. These grandchildren didn’t inherit memories of the Holocaust—at best they inherited a propensity to get PTSD. The only reason they’d even KNOW about the Holocaust is by cultural transmission from their ancestors or through reading. The events are not remembered at all, at least genetically!

So, in answer to Rossner’s title question, “Can we inherit memories of the Holocaust and other horrors?”, the answer is “we have no evidence for that”. And the subtitle’s claim that we “inherit experiences in our DNA” is just wrong. Rossner and The Daily Beast, unfortunately, have been hit by the epigenetics juggernaut, and in a way that makes them pass on completely misleading implications about inheritance. This is science reporting at pretty much its worst: a sundae of misconceptions topped with a clickbait cherry of a title.

h/t: Saul

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Dias B. G., and K. J. Ressler. 2014. Parental olfactory experience influences behavior and neural structure in subsequent generations. Nature Neuroscience. 17(1):89-96. doi:10.1038/nn.3594.