Genetic imprint from traumatic experiences carries through at least two generations.
Predictably, the study has divided researchers. “The overwhelming response has been ‘Wow! But how the hell is it happening?’” says Dias. David Sweatt, a neurobiologist at the University of Alabama at Birmingham who was not involved in the work, calls it “the most rigorous and convincing set of studies published to date demonstrating acquired transgenerational epigenetic effects in a laboratory model”.
However, Timothy Bestor, a molecular biologist at Columbia University in New York who studies epigenetic modifications, is incredulous. DNA methylation is unlikely to influence the production of the protein that detects acetophenone, he says. Most genes known to be controlled by methylation have these modifications in a region called the promoter, which precedes the gene in the DNA sequence. But the acetophenone-detecting gene does not contain nucleotides in this region that can be methylated, Bestor says. “The claims they make are so extreme they kind of violate the principle that extraordinary claims require extraordinary proof,” he adds.
Tracy Bale, a neuroscientist at the University of Pennsylvania in Philadelphia, says that researchers need to “determine the piece that links Dad’s experience with specific signals capable of producing changes in epigenetic marks in the germ cell, and how these are maintained”.
“It’s pretty unnerving to think that our germ cells could be so plastic and dynamic in response to changes in the environment,” she says.
Humans inherit epigenetic alterations that influence behaviour, too, Ressler suspects. A parent’s anxiety, he speculates, could influence later generations through epigenetic modifications to receptors for stress hormones. But Ressler and Dias are not sure how to prove the case, and they plan to focus on lab animals for the time being.
The researchers now want to determine for how many generations the sensitivity to acetophenone lasts, and whether that response can be eliminated. Scepticism that the inheritance mechanism is real will likely persist, Ressler says, “until someone can really explain it in a molecular way”, says Ressler. “Unfortunately, it’s probably going to be complicated and it’s probably going to take a while.”