Aug. 19, 1998 Tall, Independent Toddlers At Risk For Future Aggressiveness
When it comes to predicting which toddlers are the school-yard bullies of tomorrow, size does matter, according to a study in the August issue of the Archives of General Psychiatry.
"Three-year-olds -- male or female -- who average just half an inch taller than their peers tend to be more aggressive than normal when they reach age 11," says Adrian Raine, Ph.D., lead author of the study.
The same is true of toddlers who are more fearless and stimulation seeking than their peers, says Dr. Raine, a professor of psychology in the University of Southern California's College of Letters, Arts and Sciences.
Prior research has consistently shown that the most aggressive children at age 11 are more likely than normal to become violent criminals as adults -- regardless of their height at age 11.
"There appears to be a critical period in development -- sometime after age 3 but before age 11 -- when a child learns to use his physical advantage to aggressive ends," says the USC researcher into biological factors that may predispose an individual to crime, particularly violent crime. "Parents of tall toddlers -- especially those who are very stimulation seeking and fearless -- need to take extra care to drive home the message that there are a lot better ways than physical force to get what you want in life."
Raine, a clinical neuroscientist, led a team of researchers who measured the height and weight of 1,130 male and female three- year-olds in Mauritius, a racially mixed island nation in the Indian Ocean off the coast of Africa. The island's low emigration rate facilitated the researchers' ability to track the toddlers as they aged.
While toddlers, the children were ranked on several stimulation- seeking scales, including a four-point scale that tested their willingness to explore toys independently of their mother in a laboratory setting: 1) passively clings to mother; 2) shows interest in toys but stays close to mother; 3) leaves mother to explore toys but returns to mother; and 4) actively explores toys without returning to mother.
The researchers used several fearlessness scales, including a five-point scale -- ranging from 1 (representing no crying) to 5 (representing uncontrollable crying) -- to gauge how fearful the toddlers were while undergoing testing for physiological arousal.
When the children reached age 11, their mothers answered questionnaires to measure the youths' aggressiveness ("fights," "is cruel," "swears" and "threatens").
Youths ranked by their mothers in the highest 15th percentile on an aggression scale were found to have stood, as toddlers, an average of one-half inch above their peers.
Aggressive 11-year-olds had also weighed slightly more than their peers at age 3, but the link with future aggressiveness proved statistically less strong for weight than for height.
Similarly, the most aggressive 11-year-olds were found to have been more stimulation seeking and fearless than their 3-year-old peers.
"Parents of a toddler who is even slightly taller than his peers might want to be vigilant that their child does not become a pre- school bully," says Raine, author of "The Psychopathology of Crime: Criminal Behavior as a Clinical Disorder" (Academic Press, 1993).
Further study is needed to determine why height would turn out to be such a strong predictor of future aggressiveness, but Raine believes a male hormone may play some role.
"We know that people who are taller have higher testosterone levels," he explains, "so tallness in toddlers may be a marker for increased testosterone. Although the findings are debated, quite a number of studies have shown that violent offenders are higher than normal in testosterone."
If testosterone were the only key, the most aggressive 11-year- olds might be expected to stand taller than their less aggressive peers. Yet no research has ever borne out such a connection.
Social learning theory suggests a further explanation.
"A big toddler eventually learns that he can use force to get what he wants from other kids," Raine says. "So by the time the child reaches 11, aggressive behavior is ingrained -- whether he still is taller than his peers or not."
The link between a stimulation-seeking attitude and aggressiveness also merits further research, says Raine. One explanation for the connection may lie in low arousal levels in an individual's autonomic nervous system -- levels that appear to be determined either at birth or at a very young age. In earlier research, Raine showed that toddlers with low heart rates tend to be more aggressive as 11-year-olds than their peers with higher arousal rates.
"Individuals with low arousal rates appear to seek out stimulation in order to create a sort of arousal jag," Raine notes. "Just as exploring toys independently of your mother may produce a stimulation jag at age 3, so beating up another kid may produce a stimulation jag at a age 11."
Difficulty in supervising the most stimulation-seeking children might also play a role in their propensity to get into trouble as they age.
"One of the strongest predictors of delinquency is a lack of parental supervision," Raine says. "Stimulation-seeking children could more frequently get into trouble as they get older simply because they're harder to monitor than the kid who stays home and reads."
The connection between aggressiveness at 11 and a toddler's height or propensity to seek stimulation could not be explained by differences in family income, educational attainment among parents or any other aspect of the child's socioeconomic background. The link to aggressiveness at 11 was as strong for tall female toddlers as for tall male toddlers. The differences were the same for the two ethnic groups studied, Indian and Creole.
Raine warns that the findings cannot be used to accurately predict whether any particular child will or will not grow up to be a criminal.
"We're saying there are early markers -- warning signs, really -- that are predictive for future aggressiveness and possibly even for violent crime," Raine says. "But it's not a one-to-one relationship. Not every tall child is going to be aggressive, and not every stimulation-seeking child is going be aggressive. Such children are just more likely to be aggressive."
The study was conducted with support from the National Institute of Mental Health and the Ministry of Health of the Government of Mauritius.
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