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Growing up with divorce
Evidence of genetic influence on child's adjustment
  
By
Edward R. Winstead


The children of parents who divorce tend to develop their own set of problems. These kids on average have more behavioral and social adjustment problems than do other children, and many researchers attribute this phenomenon to stress and conflict in the home. A new study of divorce and children confirms the notion that environment strongly influences behavior, but it also finds evidence that parents transmit risk for adjustment problems through their genes. How the researchers got the result is an interesting story.


The study tested the hypothesis that genetics can influence how a child copes with divorce. The goal was to characterize the risk children inherit from their parents by determining how much is environmental and how much, if any, is genetic. As reported in the current issue of Developmental Psychology, the researchers analyzed data on 12-year-olds in 188 adoptive families and 210 biological families. The result, which supports previous findings on divorce and behavior, is consistent with the notion that a child's achievement and social competence are under some genetic influence.

"The effect of divorce on behavioral problems in adoptive families indicates that the event has an impact on the child," says Thomas G. O'Connor, of the Institute of Psychiatry, London. "This effect cannot be explained by a genetic mode of transmission from parent to child."


divorce runs in families

"On the other hand," he continues, "we found no effect on the general domain of social competence in the adoptive families, suggesting there may be a genetic component." By social competence, O'Connor means how well a child gets along with peers and at school.

"This study is the first to look at the effects in offspring and attempt to control for the genetic transmission of risk," says Matt McGue, professor of psychology at the University of Minnesota. "Hundreds of scientific papers," he points out, "have almost unanimously traced problems in children of divorce to environmental factors. This paper suggests there's more to it than that."

McGue, who has studied personality traits and divorce in twins and families, agrees with the basic point that genetic factors may influence a child's adjustment. But he wants to see more data. "There's no doubt that there are disadvantages to growing up with divorce," he says. "And there may be biological disadvantages involved, but the sample is too small to say unequivocally that these problems are genetically as well as environmentally transmitted."


data came from the Colorado Adoption Project

The key to the study was being able to compare the effects of divorce in both adoptive and biological families. Since biological parents transmit their genes and create the home environment, an effect that shows up only in adoptive families—and that cannot be explained by environmental factors—might be genetic. For data, the researchers turned to a unique resource called the Colorado Adoption Project, which has been collecting information on adoptive and biological families for nearly three decades. The project was founded by John C. DeFries, of the Institute of Behavioral Genetics at the University of Colorado, and Robert Plomin, of the Institute of Psychiatry, London, each of whom collaborated on the current study.

In 1972, DeFries and Plomin, then at the University of Colorado, began contacting young parents, usually the biological mother, of children who were being adopted, and gave them a series of tests. A few months later, when the child was placed, they gave the same tests to the adoptive parents. A control group of similar families was developed, and the researchers have been following the children and the families since.

Information on the 12-year-olds was obtained through interviews, standardized tests, and teacher reports. The measures included divorce, self-concept, social competence, academic achievement, the child's behavioral and emotional problems, loneliness, and substance abuse. The researchers found no association between the child's age at divorce and the level of behavioral problems.


no plans to identify specific genes

When the Colorado Adoption Project began, behavioral problems among children of divorced parents were blamed on the event itself or negative effects associated with living with only one parent. But studies done in the 1980s showed that many of these children had similar problems before and after the divorce; in addition, children who lose one parent due to death, it turned out, do not have the same problems as children of divorce. At least for some children, neither the conflict theory nor the single-parent theory fits their circumstances.

Meanwhile, it was becoming increasingly clear that divorce runs in families. During the 1990s, researchers, including McGue, found that if one identical twin becomes divorced, the chances of the other twin also becoming divorced are significantly greater than if the twins are fraternal. The inheritance of divorce, some researchers began to conclude, is really the inheritance of personality traits that tend to cause tension when certain people get together. Impulsiveness, for example, has a strong genetic component and is associated with relationship problems.

The findings in adults suggest that disruptions at home are not the whole story for children of divorce. It now seems possible that people who have difficulty with relationships may transmit to children risks for behavioral problems, and the mode of this transmission may be genetic. In an extreme example, a child's troubles could have nothing to do with the breakup of a marriage and everything to do with inherited personality traits.

The Colorado children will be followed as they enter young adulthood. Trying to identify specific genes is not an option for now, and the researchers have no plans to do so. "At this point we are trying to say that other risk factors are involved," says O'Connor. "This study is really a reminder that we need to try to avoid our tendency to focus only on the divorce event itself."

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O'Connor, T.G. et al. Are associations between parental divorce and children's adjustment genetically mediated? An adoption study. Dev Psychol 36, 429-437 (July 2000).
 

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