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Nature Vs. Nurture?

When my son, Alec, was born, I stood blissfully in the nurturist camp: I believed (as did every parent I knew) that environmental forces  -- parenting above all else  -- exerted a greater force on children than nature, or inborn traits, did. I assumed that heredity ruled our basic looks and our susceptibility to certain diseases. But our habits, foibles, values, and virtues? I thought that those were almost purely nurture, shaped by love and discipline.

Over the next couple of years, however, a few bombshells hit the zeitgeist. Just after my son turned 1, a conference on infant brain development led to a spate of news reports stating that the very wiring of our babies' minds is in our hands: The more time parents spend singing and talking to them in the first year, the more complex babies' neural pathways become, presumably leading to more success in life. Love is important, but an urgently timed barrage of words and eye contact may have greater impact.

Then, when Alec was 2, came The Nurture Assumption, a book declaring that children turn out the way they do mostly because of genes and peers. According to author Judith Rich Harris, parents matter less than they think.

In a one-two punch of hyperpublicity, these events left many parents with whiplash, feeling anxious (did we miss our window of opportunity?) and helpless (so they're learning right from wrong in the sandbox? That is, if they weren't born with psychopathic DNA).

We know that every child's temperament is significantly swayed by genes. Behavioral geneticists have been studying this link for decades. But does this fact bring our power as parents under attack, or is this an opportunity to rethink our role without seeing it as diminished?

Genetics 101

Back in high school biology, most of us were too busy giggling over the larger picture of sperm meets egg to absorb the scientific details of conception. To refresh your memory, this is the moment when, if the dance goes smoothly, 23 of Dad's chromosomes waltz off with 23 of Mom's. Divided unevenly among these 46 chromosomes are roughly 100,000 genes.

Nearly all genes travel in pairs, and some of our traits  -- whether you'll have a cleft or a rounded chin  -- emerge when one gene is dominant over its partner. For recessive traits, such as blood type O, to appear, you must inherit the same recessive gene from both parents. Other characteristics, like blood type AB, result when certain genes are codominant. But many of our physical traits, like eye color, are influenced by many genes, not just one pair.

Blood type and eye color are examples of traits that are 100 percent heritable. Height, by contrast, is between 80 and 90 percent heritable, which essentially means that environment  -- everything from conditions in the womb to childhood nutrition  -- accounts for 10 to 20 percent of the differences in height. Also, genes sometimes have what's called an additive effect: Rather than expressing, say, "tall" genes from Mom's family or "short" ones from Dad's, most children grow to a kind of genetic average.

The Roots of Personality

Studies suggest that many temperamental and behavioral tendencies are ultimately 30 to 50 percent genetic. Five major personality traits  -- called the Big 5  -- show the strongest influence: extroversion, agreeableness, neuroticism, conscientiousness, and openness to experience. Others with a significant genetic legacy include altruism, shyness, accident-proneness, and even self-esteem.

Are such tendencies present even in utero? Kimberly Saudino, Ph.D., an associate professor of psychology at Boston University who studies infant and toddler twins, says that in the first few years, there's genetic influence on three broad personality traits: activity (energy, vigor, and movement), task orientation (attention and persistence), and affect-extroversion (emotionality and sociability). Interestingly, where similar adult traits show close to 50 percent genetic influence, in babies these characteristics are only 20 to 40 percent heritable, meaning that in babyhood personality tends to be more influenced by environment.

Why? Not all genes express themselves from birth. Think of those that trigger sexual development  -- they don't switch on until your teens. When it comes to personality, Nancy Segal, Ph.D., author of Entwined Lives: Twins and What They Tell Us About Human Behavior, and her colleagues have observed that the influence of genes increases as we age.

Julia Glass is a freelance writer. Her novel Three Junes won the 2002 National Book Award for fiction.

Brain Power

Of all the traits studied by behavioral geneticists, none shows more genetic influence than IQ  -- as much as 80 percent by the time we hit old age. By testing relatives at different ages, researchers have found that IQ has a hereditary component of just 20 percent in toddlers, 50 percent in older children and adolescents, and 60 to 80 percent in older adults. Does this mean that the younger our children are, the more we can influence their mental acuity? Not necessarily, says Segal: "What you do in those early years makes a difference  -- but not in the way you may think. Providing a warm, responsive environment is your most important job, because it allows your child's tendencies and talents to flourish, but there's a limit to what you can do to affect actual IQ."

Nurture Through Nature

"When it comes to personality, genes don't determine anything," says Saudino. "They set up a range of possibilities. We know that genes influence heart disease, but if it runs in your family, do you throw up your hands and say there's nothing you can do? No. You can't change your genes, but you can choose how to live your life."

Saudino adds, "People ask me, 'Which is more important when it comes to who we are: genes or environment?' Because I'm a geneticist, my answer  -- the environment  -- surprises them." The news that our personalities are 30 to 50 percent genetic in origin seems so startling that people forget that it's less than the balance  -- which is all environment. Where do parents fit into that equation? If, as some social scientists believe, the influence of the home is minor, Mom and Dad begin to look less and less useful.

"Your 'parenting personality'  -- how you would treat any child you raised  -- appears far less important than we once thought," says Saudino. "But it's the different ways you interact with each child as an individual that are very important." Like it or not, you won't have much influence on the things you'd want any child to be: artist or athlete, do-gooder or go-getter, lover of opera or jazz. But you can definitely help them become the best people they can be. Somewhat ironically, the more you accept and respond to each child's unique tendencies as they unfold  -- the more you let her "set the pace," as Segal puts it  -- the more influence you may have in her life.

This doesn't mean being passive. A toddler who seems overly emotional or extremely shy may need special attention and guidance. Just don't expect to "overcome" such tendencies. Nor should you go overboard trying to provide your child with all the "right" stimulation and opportunities. Impart values and set limits, but don't panic at the thought that your child isn't taking the correct lessons, reading the right books, or going to the very best schools. All the extras so popular today may help, says Segal, but they won't alter a child's predisposition much.

I have a new parenting mantra: Observe, encourage, indulge. How I interact with Alec hasn't really changed since my days as a die-hard nurturist, but now I stand back and look at him with greater distance. I make an effort to support tastes and activities he has chosen, then search for ways to encourage them. It's like being a good listener: attending to a story's descriptive details, not just its plot.

Alec's love of music isn't unusual in a toddler. But last winter we discovered that he especially enjoys the sound of bagpipes. So my mother gave him a tape of the Royal Scots Dragoon Guards, to which he likes to dance most nights before bedtime. Recently, his father saw a listing for the Tartan Day Parade and too early that Saturday morning I got Alec dressed and hustled him uptown. Sitting just a foot or two from the deafening drone of those pipes, Alec  -- who objects if the TV's a little too loud  -- wore a look of rapture. Alec's first and middle names do come from ancestors, on both sides, who emigrated from Scotland. Did they carry with them genetic codes that spelled out a yen for bagpipes?

When we got home, Alec struggled to take off his coat as usual. But then, with a sigh of pleasure, he leaned on the couch and volunteered, "That was fun"  -- unprompted, for the very first time. Ask me if I felt like I mattered.