Nature, Nurture and Epigenetics: The Plot Thickens

A few posts ago I wrote about Nature vs. Nurture issues regarding homosexuality. My point was that we cannot simply ask if homosexuality is "genetic" or not. Nature and nurture interact in complex ways. Well, a recent article in Time sent to me Andrea, my graduate assistant, thickens this plot quite a bit.

The article is about epigenetics and this research appears to be revolutionizing genetic science by highlighting how environmental factors can affect the expression of genes during development.

It has long been scientific dogma that the phenotype cannot change the genotype. As John Cloud writes:

[W]e have had a long-standing deal with biology: whatever choices we make during our lives might ruin our short-term memory or make us fat or hasten death, but they won't change our genes — our actual DNA. Which meant that when we had kids of our own, the genetic slate would be wiped clean.

However, evidence has accumulated that suggests that environmental factors do affect the expression of genes. Consider the research of Lars Olov Bygren who examined the links between generational famine and life expectancy in Norrbotten, the isolated northernmost country in Sweden:

Norrbotten is so isolated that in the 19th century, if the harvest was bad, people starved. The starving years were all the crueler for their unpredictability. For instance, 1800, 1812, 1821, 1836 and 1856 were years of total crop failure and extreme suffering. But in 1801, 1822, 1828, 1844 and 1863, the land spilled forth such abundance that the same people who had gone hungry in previous winters were able to gorge themselves for months.

In the 1980s, Dr. Lars Olov Bygren, a preventive-health specialist who is now at the prestigious Karolinska Institute in Stockholm, began to wonder what long-term effects the feast and famine years might have had on children growing up in Norrbotten in the 19th century — and not just on them but on their kids and grandkids as well...

Bygren's research showed that in Overkalix, boys who enjoyed those rare overabundant winters — kids who went from normal eating to gluttony in a single season — produced sons and grandsons who lived shorter lives...Later papers using different Norrbotten cohorts also found significant drops in life span and discovered that they applied along the female line as well, meaning that the daughters and granddaughters of girls who had gone from normal to gluttonous diets also lived shorter lives. To put it simply, the data suggested that a single winter of overeating as a youngster could initiate a biological chain of events that would lead one's grandchildren to die decades earlier than their peers did. How could this be possible?

The answer seems to come from epigenes. Epigenes are cellular material that sit atop the genome and affect how the genes switch on or off during development. Apparently, while environment cannot affect the actual DNA it can affect the epigenes which, in turn, affect how the genes are expressed. Think of our DNA as the keys on a piano. They are fixed. The epigenes are like the piano music. They can play Mozart or Jazz. The basic notes are the same but the music can be very different.

And what is very important to note, if you read Cloud's article to the end, is that many of these epigenetic changes don't just affect you. They affect your children. Your choices often have generational consequences modifying the bodies and minds of your children and grandchildren.