The latest issue of the journal Science has an essay by Greg Miller looking at the explosion of research into epigenetics and what this work could suggest about human society.
In 2004, Szyf and Meaney published a paper in Nature Neuroscience that helped launch the behavioral epigenetics revolution. It remains one of the most cited papers that journal has ever published. The paper built on more than a decade of research in Meaney’s lab on rodent mothering styles.
Rat moms vary naturally in their nurturing tendencies. Some lick and groom their pups extensively and arch their backs to make it easier for their young to nurse. Others spend far less time doting on their pups in this way.
Meaney had found that the type of mothering a rat receives as a pup calibrates how its brain responds to stress throughout its life. Rats raised by less-nurturing mothers are more sensitive to stress when they grow up.
This research demonstrated that the environment plays an important part in biological development and that offspring can even “inherit” the effects of a mother’s environment.
Whereas a nurturing environment can predispose a rodent to be calmer in adulthood and raise a nurturing family of its own, an adverse environment can have the opposite effect. There’s evidence that this effect, too, may involve epigenetic changes. Last year, researchers led by Tania Roth and J. David Sweatt of the University of Alabama, Birmingham, helped show this by building on earlier work showing that rat mothers denied access to the materials needed to make a proper nest become anxious and spend less time nurturing their young. Pups raised by these stressed-out rat moms exhibited increased methylation of the gene for BDNF, a neural growth factor, in the brain’s prefrontal cortex, they reported in the 1 May 2009 issue of Biological Psychiatry. In addition, this methylation pattern, which would tend to reduce the amount of BDNF produced, was passed on to the subsequent generation.
This research could have important implications for our own society. The United States has the highest levels of inequality in the so-called “developed world” and one-third of Americans suffer from extreme stress, according to the American Psychological Association.
If the rodent research on epigenetics translates to humans, the implications could be far-reaching. The effects of adverse environments early in life are well documented and notoriously hard to shake. Childhood abuse, for example, elevates the lifelong risk of depression, anxiety, and suicide. Growing up in an impoverished environment also takes a lasting toll, affecting physical health as well as behavior. Could epigenetics be part of the reason?
Miller shows that, so far, the evidence to support a direct epigenetic connection between a stressed population and societal problems has yet to be clearly demonstrated. However, this research suggests that how resources are distributed can have long-lasting effects on the next generation.