Epigenetics: From Heresy to Fact?
A paper published in Nature early this week declared that learned fears can be inherited through multiple generations of mice.
Yes, this sounds an awful lot like Jean-Baptiste Lamarck’s long-discredited theory of the heritability of acquired characteristics, and yes, it is throwing scientists into disarray. Journalist Virginia Hughes captured some of the tweets that followed the news: “This is insane. Lamarckism, simply.” “Crazy Lamarkian shit.” “Astonishing if true.”
Here’s what happened: Emory University neuroscientists Kerry Ressler and Brian Dias trained mice to fear the smell of a specific chemical by exposing them to the scent while giving them small electric shocks; eventually the mice learned to fear the smell without the shocks. This kind of Pavlovian conditioning is routine. What is remarkable is that the learned fear reaction was passed down through two subsequent generations. Without ever having encountered the smell in their lives, the mouse pups exhibited the same reaction of fear around the scent, while a control group of pups did not.
What’s more, the brains of the mice were altered – they somehow had more neurons and bigger signal-receiving structures to help them detect the scent. According to Dias, “The overwhelming response has been 'Wow! But how the hell is it happening?'"
The answer to that question, Ressler, Dias and others believe, lies in “epigenetics,” the way in which traits can be inherited through changes in gene expression caused by mechanisms other than changes in the underlying DNA sequence.
There is, and will surely continue to be, a lot of skepticism about this kind of behavioral epigenetic research. The authors of the paper haven’t been able to identify a biological mechanism to explain how it actually works. But what would have simply been laughed at ten years ago is certainly gaining credibility as the field of epigenetics matures, and studies begin to mount.
The idea that the environment can modify how genes are expressed is fairly well accepted now. For example, surviving a famine as a fetus seems to increase the risk of getting certain diseases as an adult.
There have also been other studies that show transgenerational epigenetic changes in animals. A study of rats from the University of Texas, for example, suggests that exponential rises in obesity, diabetes, and autism in humans could be due to our grandparents’ exposure to chemicals in plastics, fertilizers and detergents. Other papers from 2010, 2011, and 2012 suggest that diet and stress can impact future generations.
But the inheritance of behavioral modifications could be the most controversial of all. And Ressler and Dias suspect that this phenomenon isn’t limited to mice.
The implications of this are pretty huge. It means that the experiences of our recent ancestors have left what could be called “molecular scars” on our DNA and on our lives, and that we will do the same to our children and grandchildren. This requires the reconsideration of much of what our biology textbooks taught us, and it will impact everything from medical research, to sociology, to neuroscience. As an article in The Telegraph put it earlier this year, “the idea is heretical.” But it seems to be one that’s here to stay.
Previously on Biopolitical Times: