Nature and Nurture

Nature or nurture. Is it our heredity or our personal, social, and physical environments that have the greatest influence on our health? And, for that matter, is it nature or nurture that most affects the person each of us becomes, the person who decides what is a full, rich life?

The completion of the Human Genome Project seemed to hold great promise for identifying disease risk through genetic testing. Going further, great hope was and continues to be held for personalized medicine: your genome enabling doctors to decide what drugs would work best on you.

The idea was simple: using the map of the human genome, scientists would identify specific gene variations associated with increased risk of getting a disease. This is done by comparing DNA sequences of people with specific conditions to people without them. Every week there seems to be a new report of such associations—last week, genes associated with increased risk for diabetes were found to be the same genes associated with a reduced risk for inflammatory bowel disease in an apparent genetic collision.

With these scientific promises, a new market was developed to sell such tests directly to consumers. However, as an article on the business page of the New York Times reported recently, there aren’t many customers—although hopes remain buoyant. One company is taking the clever strategy of shifting its pitch from consumers to doctors. The logic is compelling and it’s a strategy already used by the pharmaceutical and nutraceutical industry.

The strategy fits well with current medical practices. In the aftermath of the recent national healthcare reform legislation, much has been made about provisions for prevention. These are rather sad provisions, such as requiring insurance companies to pay for free annual physicals with the usual host of screening tests, despite the dangers for overdiagnosis and overtreatment—the two factors most responsible in my opinion for escalating medical costs and undermining actual health. With an effective sales strategy directed at physicians, yet another layer of pseudo-prevention will be targeted at us.

As we discuss in Too Much Medicine, Not Enough Health, the problem with these genetic tests is that the science has passed them by. The tests are based on the idea that a gene expresses itself by producing a protein that goes off into the body and does some piece of work—or in the case of disease, some piece of mischief. There are two aspects to this high concept that are wrong.

The first is that the body has something like half a million distinct proteins while the human genome consists of only about 23,000 genes. Where do all those extra proteins come from? From the action of proteins on proteins and other biochemicals on proteins. Consider a house. It’s built from blueprints. The newly finished house doesn’t look exactly like the blueprints. And after it’s been lived in, it looks even less like the blueprints. To say nothing of how the house behaves when it’s actually lived in at the location where it was actually built.

The second thing that’s wrong with the high concept of one gene makes one protein is that in fact many genes are involved in getting a piece of bodily work (or bodily mischief) done. This still looks like fate by DNA, only more complicated, but it’s not. Three mechanisms affected by environmental factors determine how the blueprints get drawn, modified, and turned into someone’s biological home. These mechanisms affect how DNA unwinds to build an organism. They are the action of hormones, symbiotic relationships with other organisms, and nutrient and biochemically induced DNA methylation. Allow me to point out that each of these is part of an organism’s normal development. Organisms are adapted to respond to these influences in order to better lead a full, rich life.

So the fundamental principal on which these new genetic tests are based is simply wrong.

From an evolutionary standpoint, it makes perfect sense that our inherited traits as written in our DNA unfold in response to the environment in which we develop. In the case of mammals, that’s as fetuses in the womb. It also happens again during sexual maturation following puberty. Once we’re mature, we pass on to our children the nature that our environment has shaped. In addition, we ourselves affect the environments in which our children develop and mature—the environments that build their nature.

Some recent research has demonstrated that the methylation process, for example, is what’s called evolutionarily conserved—that is, passed from generation to generation and occurs across all plant and animal species. In other words, the evolutionary process handed us the ability to adapt our nature to our environment. In a complementary fashion, all creatures work to change their environment to suit their needs and in so doing change their nature. Humans happen to be exceptionally talented at doing this.

So nature or nurture is a false dichotomy. It’s not one or the other. Nor is it 50% nature and 50% nurture. Instead, who we are is a confluence of nature and nurture. We each have a nature, but it’s what we have to work with, not what we’re cursed to suffer as reported to us by a test of little scientific merit.