The Genetics of Temperament-An Update

There are a lot of temperamental Jerome Kagan moments in my friend’s household-an observation that will require this entire column to explain. What exactly is a temperamental moment? And who exactly is Jerome Kagan?

Before we start, it might be useful to know that my friend’s household consists of a husband, a wife, and 2 little girls, aged 6 and 9. Their temperaments could not be more different. The 6-year-old is little Miss Sunshine-socially fearless, prone to risk taking, ebullient, confident. She will charge into a playroom full of strangers, initiate 2 conversations at once, quickly survey all the toys in the room, and then lock down on the dolls, playing with them for hours.

Her big sister behaves in exactly the opposite way. She seems fearful, tentative, cautiously tiptoeing into the same playroom after only reluctantly leaving her mother’s side. She will then find some safe corner and just sit there. It is a bit sad to watch; this older girl seems to show no interest in exploring, hardly speaks at all, and appears scared if somebody tries to talk to her. She is extremely averse to taking risks of any kind.

The younger daughter doesn’t have a shy bone in her body. The older daughter appears highly reactive, anxious, and afraid. Yet, they both come from the same family. What is the difference between these 2 kids?

Psych 101

A partial answer comes from the laboratory of legendary psychologist Jerome Kagan, in case you’ve forgotten your Psych 101. Many years ago, Kagan noticed that babies seemed to fall into a reactivity continuum. Some kids at one end of the spectrum behaved like my friend’s self-confident 6-year-old girl. At the other end resided kids who were like the self-doubting 9-year-old. And there were kids whose behaviors fell between the extremes.

Temperament provides the emotional and behavioral building blocks on which adult personalities are constructed.

Kagan was the first to posit that where a child sat on this continuum-a description of one dimension of their temperament-was in large part hardwired-or at least, observable shortly after birth and mightily resistant to change. These traits may even be genetic. Now that several longitudinal studies have matured and their research paybacks have long since been cashed, Kagan’s insights have been shown to be well-placed. Temperament is resistant to change, depending on how you define it, and there may even be a few genes that help explain the behaviors. Because it may have been a while since your last psych class, I thought you’d like an update.

We will begin by briefly reviewing the definition of the notion of temperament, spend some time discussing Kagan’s initial experiments, then move to a genetic system that shows great promise in helping to describe the DNA behind the behavior. Feel free to skip to the section, “The gene work,” if Kagan’s great body of research is part of your vocabulary.

A review of temperament

In the cognitive neurosciences, temperament is a multilayered concept. It is often defined as a person’s characteristic way of responding emotionally and behaviorally to external events. These responses are fairly fixed, innate, and observable soon after birth and may have genetic components. Personality is defined as not being so immutable. It is shaped primarily by the parental and cultural factors into which a child is born and raised.

Personality is influenced by temperament, the same way a house is influenced by its foundation. Many researchers believe temperament provides the emotional and behavioral building blocks on which adult personalities are constructed.

There is some real controversy about the edges of these definitions, of course-conflicts typical of the “nature/nurture” battlefields researchers have been fighting for decades. Jerome Kagan was really the first to sink some empirical teeth into an argument previously based on opinion. He screened 400 kids way back in 1979, doing experiments in places similar to the rooms in which the 6- and 9-year-olds mentioned above were playing. He found about 15% acted like the younger daughter (behaviorally ebullient, or low-reactive [LR]) and another 15% acted like the older daughter (behaviorally inhibited, or highly reactive [HR]). He measured a subset 5 years later and found things were remarkably stable. Only 3% of the children had actually changed categories.

Kagan next investigated 500 kids starting at 4 months of age, coding them using the same LR or HR behavioral algorithms as before. He retested these same kids at 4, 7, 11, and 15 years (the experiment is still ongoing, although Kagan has retired and bequeathed the work to another colleague). He found that HR babies were 4 times more likely to be behaviorally inhibited by age 4 (like my friend’s older daughter). By age 7, some form of anxiety had developed in half of these kids, compared with 10% of the control HRs (who made up about 20% of the population).

As HR kids navigated through school, Kagan noticed most were academically successful, even if they were a bucket of nerves. They got good grades and made lots of friends. They were less likely to experiment with drugs, to get pregnant, or to drive recklessly-perhaps because of an anxiety-driven need to acquire compensatory mechanisms to socialize properly. Kagan actually liked HR people and regularly employed them during his research career. “I always look for high reactives,” he told The New York Times in 2009. “They’re compulsive, they don’t make errors, they’re careful when they’re coding data.”

Kagan’s conclusion? Babies come into this world with an inborn temperament. About 20% are born with a predisposition to anxiety-a behavioral type that remains remarkably stable over time. Kagan calls this the long shadow of temperament.

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