Nature-Nurture: Recasting who we are, how we got that way

Since Sir Francis Galton coined the phrase “nature versus nurture” 150 years ago, the debate about what makes us who we are has dominated the human sciences.

Do genes determine our destiny, as the hereditarians would say? Or do we enter the world as blank slates, formed only by what we encounter in our homes and beyond? What started as an intellectual debate quickly expanded to whatever anyone wanted it to mean, invoked in arguments about everything from free will to race to inequality to whether public policy can, or should, level the playing field.

Today, however, a new realm of science is poised to upend the debate — not by declaring victory for one side or the other, nor even by calling a tie, but rather by revealing they were never in opposition in the first place. Through this new vantage, nature and nurture are not even entirely distinguishable, because genes and environment don’t operate in isolation; they influence each other and to a very real degree even create each other.

The new field is sociogenomics, a fusion of behavioural science and genetics that I have been closely involved with for over a decade. Though the field is still in its infancy, its philosophical implications are staggering. It has the potential to rewrite a great deal of what we think we know about who we are and how we got that way. For all the talk of someday engineering our chromosomes and the science-fiction fantasy of designer babies flooding our preschools, this is the real paradigm shift, and it’s already underway.

Picture a kid who is born with two working copies of what’s known as the sprinter’s gene, ACTN3. By elementary school, she might be winning every game of tag, every race. By high school, she makes varsity track and soccer, and the more she excels, the more coaching and training is made available to her. Of course, any number of factors might cause her to quit sports — an injury, say, or a toxic team environment. But if she keeps at it, her starting position on a big college team won’t be the result of just her genes or her hard work. It will also be the result of how her genes shaped her environment, influencing the people and opportunities she encountered, and how her environment shaped the way and the degree to which her genes expressed themselves. It’s a continuous feedback loop, in which neither nature nor nurture is a fixed entity.

At other times, the nature-nurture feedback loop may be more pernicious. It’s no surprise that terrible setbacks — the loss of a job, the end of a marriage — can cause people to fall into depression.

The part of this research that blows me away is the realization that our environment is, in part, made up of the genes of the people around us. Our friends’, our partners’, even our peers’ genes all influence us. Preliminary research that I was involved in suggests that your spouse’s genes influence your likelihood of depression almost a third as much as your genes do. The social environment, then, is genetics one degree removed. And vice versa.

When scientists started decoding the human genome, many assumed the nature-nurture debate was over and the hereditarians had essentially won. Soon we’d know the genetic blueprints for everything: obesity, intelligence, susceptibility to chronic diseases, even individual personality traits. Pharmaceutical companies would develop drugs that could target the handful of genes responsible for, say, arthritis or heart disease or schizophrenia. The end of illness would soon be at hand.

Scientists don’t all agree about what to make of this new data or whether it can apply equally to all populations, but today roughly 6,000 studies have identified polygenic indexes, or PGIs, for more than 3,500 traits, from sleep habits to right- or left-handedness and extroversion.

At the same time, it’s far from destiny. Clearly, genes alone are not enough to explain the course of people’s lives, even if someday we get much better data than this nascent field can currently provide.

So what, then, should we do with those PGI scores, which — as the field of sociogenomics reveals — tell us so much and yet so little?

If doctors start using them to identify people at high risk for heart disease and get them started on preventive regimens long before they’re in danger, the benefit would be pretty uncontroversial. What if life insurance companies start adjusting premiums based on genetic risk for stroke? That’s more complicated. Even the historical era and social conditions into which a child is born — their environment writ large — can affect how their genes do or do not find expression.

(Dalton Conley, a sociology professor at Princeton and a faculty affiliate at the New York Genome Center, is the author of 'The Social Genome: The New Science of Nature and Nurture')

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