We May Inherit Our Fears

It can be hard to figure out where our fears and anxieties come from, but perhaps we should look to our own history for answers. A new study published in Nature Neuroscience suggests that your fears could be passed on to your children and your children's children, a finding surprising enough to stir up some controversy. The study proposes that this occurs through something called transgenerational epigenetic inheritance.

So what exactly is transgenerational epigenetic inheritance? According to Nature Reviews Genetics, it can be defined as "effects on a phenotype (or on patterns of gene expression) that are passed from one generation to the next by molecules in the germ cells and that cannot be explained by Mendelian genetics (or by changes to the primary DNA sequence)." Or in simpler words, epigenetic modifications "alter the expression of genes, but not their actual nucleotide sequence."

How does this apply to fears? Researchers Brian Dias and Kerry Ressler of Emory University demonstrated the supposed inheritability of fear by conditioning male mice to fear a certain smell, that of a chemical called acetophenone. Ten days after conditioning, these mice, the F0 generation, were allowed to mate. Their babies, the F1 generation, showed sensitivity to the odor of acetophenone, a scent they had previously not experienced. When the F2 generation came along, they showed a similar sensitivity.

What is crucial here is that the environmental conditioning took place well before conception and so the original fear induction did not directly affect the F1 offspring as they developed within their mothers.

Behavioral results in hand, Dias and Ressler also wanted to see if there was any neuroanatomical basis for this transgenerational sensitivity. They found that in comparison with those animals who hadn't been conditioned, the conditioned mice had more acetophenone-responsive neurons as well as larger brain structures corresponding with the chemical. Furthermore, sperm also showed signs of heightened activity in response to the chemical.

The unusual results were further supported by experiments involving in vitro fertilization and cross-fostering in an attempt to eliminate the influence of external influences, like "social transmission."

Do these results have anything to offer for humans? As an adopted person who is chronically anxious, my mind is tempted to run amok with the potentials of this research. Could this be another possible explanation for my incessant tendency to worry or my biggest phobia?

Well, maybe, but we can't say just yet. Jumping to any conclusions about my, or any other human's, mental state based on the olfactory fears of lab animals seems wildly premature, if not totally irresponsible. Mice are not humans, so we cannot simply map these results onto the human species. However, the researchers are hopeful that future studies may provide some clues.

"Such a phenomenon may contribute to the etiology and potential intergenerational transmission of risk for neuropsychiatric disorders, such as phobias, anxiety, and post-traumatic stress disorder," write Dias and Ressler. But that doesn't mean we inherit memories of fear. As Dias told Virginia Hughes over at National Geographic, "I don't know if it's a memory. It's a sensitivity for now."

Fascinating as the data in the paper may be, it is not without its skeptics. Criticisms hinge mainly upon two factors. First, there's the researchers' inability to describe the mechanism by which the sensitivities manifest. As has been the case with similar studies, a definite molecular mechanism behind transgenerational epigenetic inheritance is elusive. Secondly, even the slightest whiff of Lamarckism—think of the giraffe necks—gives some scientists pause.

Objections to the work are summed up best by the comments that Timothy Bestor, a molecular biologist stationed at Columbia University, shared with Nature.com. "The claims they make are so extreme they kind of violate the principle that extraordinary claims require extraordinary proof." But his statements are countered by other scientists, who have called the work "awe-inspiring biology" and "compelling."

Despite the division amongst their peers, Dias and Ressler insist that this plus data from other studies does in fact "emphasize that transgenerational epigenetic inheritance does occur in mammals." And they are already designing plans for their next project as Dias explained to Hughes: examining whether or not a fear learned and then unlearned in a parent generation would get passed on to offspring.

@heyiamlex