Nuture And Nature Both Shape Acting-Out Behaviors

Genetics gets more than it’s fair share of attention these days. This isn’t a bad thing — except that it seems like studies that focus on the environment don’t get the same play. So here’s one recent paper you should know about.

Drs. S. Alexandra Burt and colleagues studied acting-out behaviors in adoptive and biological adolescent sibling pairs. Siblings and their parents were videotaped while being asked to talk about two topics (one focused on the meaning of a Rorschach inkblot, the other on what to make of a moral dilemma). The idea was to see how teens behaved during conversations with their parents and their brother or sister, especially ones that could promote differences of opinion. Observers later viewed the videotapes and rated a number of acting-out behaviors for each adolescent, including things like getting angry, talking back, and whining.

The key thing about having adoptive and biological siblings is that it provided a method for inferring the role of genes and the role of environment. Here’s how it works. The researchers used a statistical method to see how similar each sibling pair was on the rated acting-out behaviors. In other words, if one sibling used a lot a acting-out behaviors, how likely was the other sibling to do the same?  If genetics was the only factor that influenced sibling similarity, then the adoptive siblings should, on average, not resemble each other very much (so that one sibling acting out a lot wouldn’t be associated with the other sibling doing the same). If genes did not play a role, then biological siblings should not be, on average, more similar in their acting-out behaviors than adoptive siblings.

Using this approach, Dr. Burt and colleagues found evidence that supported roles for both nature and nurture. Biological siblings were more similar than adoptive siblings, suggesting that genes do indeed make a contribution. However, adoptive siblings were also similar in their acting-out behaviors (at a statistically signifcant level), suggesting environmental influence independent of whatever role genetics may play.

These results are important for parents to consider because they remind us that although genes contribute to behavioral development, nature isn’t the only thing that matters. In my next post, I’ll discuss some of the environmental factors that may lead to acting-out behavior — and what parents can do about them.

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