Biological orthodoxy has always held that we inherit our genes from our parents, and those genes come from the DNA that they were born with. So nothing that happens to them during their lives can be biologically passed down to us.
But new research is suggesting that an individual's life experiences can in fact affect the way their offspring's genes are going to be expressed. Article in Tufts Now here.
Scientists are discovering that a parent's experiences can lead to changes in gene expression that are encoded in the sperm or egg and passed to offspring. In other words, there is a way in which offspring inherit the experiences of their parents. This is different than inheriting genes for brown or blue eyes. It's more like inheriting genes that are switched on or off for the purpose of being better adapted to a particular environment.
Larry Feig, professor of developmental, molecular, and chemical biology at Tufts University School of Medicine, has done experiments with mice in which males are exposed to the stress of frequent rearranging of social groups. This led to different levels of microRNA molecules in their sperm.
After the sperm has fertilized the egg, these microRNA molecules give directions about how genes are expressed in the developing embryo. In the sperm of the stressed mice and early embryos derived from them, Feig found that two specific microRNA molecules occur at much lower levels than those from non-stressed mice.
The female offspring of these stressed mice show more anxious behavior than normal. The male offspring don't; however, they do have the same changes in their sperm, even though they weren't stressed themselves. And their female offspring are anxious.
These types of changes in gene expression are called epigenetic changes.
At the right levels, this could confer benefits to a parent's offspring. One can imagine that if conditions in the world are adverse, anxious and fearful behavior could be advantageous to one's offspring. Conversely, if the parent's world is not stressful, more bold and fearless behavior could be the more beneficial strategy. Epigenetics would pre-arm offspring by conferring on them, from birth, the "correct" disposition for their environment they are born into.
But Feig is investigating how this system could go awry. "The idea is that under normal circumstances, it's a good thing," Feig says. "Like any other regulatory system, if it's in excess, it could cause harm."
Feig is interested in conducting a study in humans to see whether people who experienced childhood trauma might pass epigenetic changes that make their children more susceptible to psychiatric disorders.
"If certain microRNA changes make the next generation susceptible to psychiatric disorders," he says, "you might be able to reverse those changes, by therapy, meditation or antidepressants, before people have kids. It's much easier to change epigenetics than genetics, because epigenetic regulation of genes, including those that control sperm microRNA levels, responds to the environment."
Research in this field has yielded some surprising results. A 2019 Swedish study showed that people who had access to an over-abundance of food during their prepubscent years because of favorable harvests, had grandchildren who were more susceptible to cancer, with their lives shortened by six years.
There is also the case of the Dutch Hunger Winter. Toward the end of World War II, the German-controlled Netherlands held a railway strike to aid the Allies' advance. The Germans retaliated with a food embargo to the Western Netherlands that caused a drastic food scarcity in the winter of 1944-1945.
Fetuses whose mothers were exposed to the famine only early in pregnancy, but not during the later months of pregnancy, were able to recover and were born at normal weights. But those children became more likely to have obesity and mental health problems throughout their entire lives. And then some of those effects were present in those people's children, the grandchildren of the pregnant women who suffered through the famine. Link to the Natural History article here.
It does seem to me that when doing these studies involving humans, it would be difficult to tease out the effect of parental behavior. Parents who were under great stress during their childhood might be more likely to exhibit different kinds of parenting behavior when raising their children that could lead to certain psychological and physical health outcomes for those children.