If I say, "Twin studies, adoption studies, and so forth suggest that for a lot of traits, there's roughly a 50-50 breakdown between the effects of heredity and environment, over the last few years," I constantly get told that: "Oh, no, that's so 20th Century. You see, some of the genes are also being affected by the environment."
Me: "Okay, but that still leaves us with the results of twin and adoption studies. So, what it sounds like you are saying is that genes aren't just 50% of the importance, they're something like 75%, but maybe 1/3rd of the genes are influenced by the environment, so we're right back to 50-50, right?. I mean, we have to get back to what the studies report."
For example, here's Helen Fisher, a biological anthropologist at Rutgers, writing in literary agent John Brockman's annual January question confab at his Edge.org:
To me, epigenetics is the most monumental explanation to emerge in the social and biological sciences since Darwin proposed his theories of Natural Selection and Sexual Selection. Over 2,500 articles, many scientific meetings, the formation of the San Diego Epigenome Center as well as other institutes, a five-year Epigenomics Program launched in 2008 by the National Institutes of Health, and many other institutions, academic forums and people are now devoted to this new field. Although epigenetics has been defined in several ways, all are based in the central concept that environmental forces can affect gene behavior, either turning genes on or off. ...
The consequences of epigenetic mechanisms are likely to be phenomenal. Scientists now hypothesize that epigenetic factors play a role in the etiology of many diseases, conditions and human variations—from cancers, to clinical depression and mental illnesses, to human behavioral and cultural variations.
Take the Moroccan Amazighs or Berbers, people with highly similar genetic profiles who now reside in three different environments: some roam the deserts as nomads; some farm the mountain slopes; some live in the towns and cities along the Moroccan coast. And depending on where they live, up to one-third of their genes are differentially expressed, reports researcher Youssef Idaghdour.
For example, among the urbanites, some genes in the respiratory system are switched on—perhaps, Idaghdour suggests, to counteract their new vulnerability to asthma and bronchitis in these smoggy surroundings. Idaghdour and his colleague Greg Gibson, propose that epigenetic mechanisms have altered the expression of many genes in these three Berber populations, producing their population differences.
Genes hold the instructions; epigenetic factors direct how those instructions are carried out. And as we age, scientists report, these epigenetic processes continue to modify and build who we are. Fifty-year-old twins, for example, show three times more epigenetic modifications than do three-year-old twins; and twins reared apart show more epigenetic alterations than those who grow up together. Epigenetic investigations are proving that genes are not destiny; but neither is the environment—even in people.
Okay, but we already knew that genes are not destiny, but neither is the environment.
I am hardly the first to hail this new field of biology as revolutionary—the fundamental process by which nature and nurture interact. But to me as an anthropologist long trying to take a middle road in a scientific discipline intractably immersed in nature-versus-nurture warfare, epigenetics is the missing link.
I'm not saying that it isn't valuable to know that one way the environment affects traits is through sending a message to the genes to turn themselves on or off, but that that doesn't tell us anything terribly significantly new about what people get hot under the collar about: the limits of environmental influence.