Child Development

How Much Of Child Development Is Nature Vs. Nurture?

The nature vs nurture debate is settled: Personality traits are heritable. But how much of child development hinges on DNA, and what should parents do with this information?

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A dad holding his two kids in his arms and smiling.

You have your mother’s eyes, your father’s temperament, your grandfather’s way with language, and your grandmother’s personality — or maybe not. It’s possible those claims, echoing through the course of your childhood, became a self-fulfilling prophecy. It’s all part of the nature vs nurture debate, a story that is often oversimplified in child development by making broad generational comparisons. And those comparisons can be misleading, if not downright damaging, precisely because they conflate fate and genetics.

According to David Rettew, M.D., a child psychiatrist at the University of Vermont, telling children their personalities are predetermined by their DNA can be harmful — true or not. Though scientists now suspect that personality traits are closely tied to genetics, Rettew suggests parents emphasize that negative qualities can be changed, and that nature and nurture work in close concert.

“As long as you don’t suggest some kind of inevitability, it can be useful for kids to have some idea of what their personalities tend to be, and that [any given trait] is around 50% nature and 50% nurture,” Rettew says. “But I believe it is a parent’s job to increase the possibilities for a child. Telling a kid they’re going to end up just like a parent can be confining.”

Besides, it’s not as though the split between nature and nurture is easy to break down or break apart. There is no one gene for any personality quirk, Rettew explains. “It’s more likely that it’s dozens, if not hundreds, of genes with each one having a small effect that can add up to whether or not you have more or less of a given trait,” he says. More complicated still, a child’s personality develops based on the interplay between genetics and the environment.

Complexity notwithstanding, researchers have conducted hundreds of studies on behavioral genetics in an attempt to assign genetic and environmental determinants to what makes us tick. The culmination of that work came in 2000 when Eric Turkheimer of the University of Virginia published The Three Laws of Behavioral Genetics. “The nature-nurture debate is over,” Turkheimer announced in his paper on the subject. “The bottom line is that everything is heritable, an outcome that has taken all sides of the nature-nurture debate by surprise.”

A Practical Primer on Behavioral Genetics

The first law of behavioral genetics is that all human behavioral traits are heritable; the second law is that the effect of being raised in the same family is smaller than the effect of genes. The third law merely qualifies the fact that much of the complexity of human behavior is not accounted for by genes or families.

Five years later, a team of behavioral geneticists proposed a fourth law, which accounted for advances in molecular biology: “A typical human behavioral trait is associated with very many genetic variants, each of which accounts for a very small percentage of the behavioral variability.” In other words, it takes many genes to create one personality trait.

So are children genetically predisposed to certain traits? “The answer is clearly yes,” explains Philipp Koellinger, Ph.D., a professor of social science genetics who studies how genes influence economics at the University of Amsterdam. “Children resemble their parents both for genetic and for environmental reasons, but genetics contribute to almost all traits to some extent, even for things like subjective well-being or political affiliation.”

And those influences only become stronger with time. “You’d think the longer the environment has a chance to exert its effects, the more it would overcome the genetics,” Rettew says. “But it doesn’t seem to work that way. Intelligence, even personality traits…We have found that genetic influences get stronger as you get older.”

At the same time, one cannot discount the impacts of parenting style and environment upon the developing personality. “While kids do resemble their parents, they are not carbon copies of their parents,” says Theodore Wachs, Ph.D., a psychologist at Purdue University who studies child development. “If only because the environmental context, broadly conceived, that kids grow up in may be quite different from the environmental context their parents grew up in.”

This is not a contradiction to the laws of behavioral genetics, because genes do not operate in a vacuum. A child may be genetically predisposed to anger (nature). But when this child is disciplined, the environment (nurture) may mitigate it in the long term. Or, conversely, an angry child may anger their parents, fueling the fire.

“It is futile to try to separate developmental influences on children into nature and nurture,” says George Holden, Ph.D., chair of the department of psychology at Southern Methodist University. “Both influences are constantly interacting with each other.”

Put differently, dads may give their kids their angry streaks. But their parenting plays a large role in determining whether it fizzles out in childhood or boils over into adulthood.

Parenting With the Power of Behavioral Genetics

The question is what to do with this information. Our children are, for better or worse, just like us. And although nurture can change that, a lot of those environmental effects are on us, too. Through nature and nurture, we mold our children’s personalities. Should we let them know?

Favorable comparisons are generally safe. “If parents are sensitive and empathetic toward their child, being compared to that parent would be viewed as positive by the child and enhance their sense of self-esteem,” Wachs says. “If parents display traits like persistence in the face of adversity, children who feel, or are told, they are like that parent may develop the same trait.”

But even the most well-intentioned words can backfire. “Telling a child that he or she is just like a parent denies some of their individuality,” Wachs says. “A child may feel a sense of ‘predestination’ or inevitability to turn out one way or another.” In moderation and within the context of a healthy relationship, however, telling your kids that they share your positive qualities is probably fine. “In my day-to-day world as both a parent and child psychiatrist, I don’t encounter a lot of kids expressing concern that they’re destined to be like their parents,” Rettew adds.

Less favorable comparisons are, naturally, much riskier territory. “If parents are hostile and rejecting of the child, children may not want to be seen as like that parent, and a remark that you’re just like mom or dad may come across as negative and perhaps reduce the child’s sense of self-esteem,” Wachs says. “Similarly, if a parent is brilliant and a high achiever, when compared, their child may feel they cannot measure up to the parent and may not try.”

A dysfunctional situation at home can also be aggravated by bringing genetic predisposition into the mix. Some parents may attribute normal child behavior to a quality that they do not like in their spouses, for instance, and this can lead to abuse. Perhaps a baby screaming for milk is self-centered, just like her mother. Or a toddler is throwing tantrums, just like his father.

“Because the parent is processing the behavior in that negative way, the parent is unlikely to provide for the needs of the child,” Holden says. “That could result in the child continuing to behave in that way. In extreme cases, it can result in child neglect or physical abuse.”

One healthier way to integrate the science of nature and nurture into parenting is to highlight effort over disposition. When a child does well in school, for instance, noting that they are genetically predisposed to intelligence and were raised by smart parents is not nearly as productive as highlighting their hard work.

“The better message is to recognize the work they did to earn that good grade,” Holden says. “This message has been shown to predict better long-term outcomes in children than the outcome-oriented message, i.e., ‘You are smart.’”

Another strategy is to teach a child that they’re more than a collection of personality traits. Parents who reprimand kids for their actions without implying that those actions are fundamentally a product of supposedly immutable traits clearly communicate to children that they are in charge of their own behavior. And it’s true. Impulses can be ignored; genetic predispositions, even when bolstered by environment and life experience, can be controlled.

“If you have a 3-year-old who has a tendency to hide behind his mom’s legs when strangers show up, instead of saying ‘you are shy’ say ‘you’re acting shy right now,’” he says. “There’s value in not suggesting that this is who they are — this can be self-limiting.”

“You don’t want your words to become your child’s narrative.”

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