Vol. 8, No. 1, 2002 Page 3&6
A review of new and novel hypotheses about the origins and treatment of violent, criminal, or aberrant behavior.
Juvenile delinquency rose from 1987 to 1991, and decreased almost continuously from then through the end of the 1990s. Researcher Jacob Orlebeke theorizes that these changes may stem, in part, from changes in the average age at which women gave birth in earlier decades.
Several studies have shown that children of older mothers exhibit less "externalizing" behavior (aggression, overactivity, and defiance). "This is a statistically very robust linear association," Orlebeke says, "which extends over the whole age range of mothers." In addition, research shows that children who do exhibit externalizing behavior are at increased risk for later delinquency.
Based on these findings, Orlebeke theorized that children of younger mothers would be more likely to become delinquents than children of older mothers. Comparing juvenile crime data to maternal age data, he found that the two sets of figures are closely correlated, with drops in maternal childbirth age correlating with increases in delinquency 17 years later, and increases in maternal childbirth age associated with drops in delinquency 17 years later.
It is possible, Orlebeke says, that the difference in delinquency rates stems from older mothers having different parenting styles than their younger counterparts. However, he suggests another reason for the link between older maternal age and reduced delinquency: younger mothers expose their children in utero to higher levels of testosterone (a "masculine" hormone present in small but significant amounts in women).
"The serum testosterone level of women of 20 years is about twice the value [of that] in women 40 years of age," Orlebeke notes, adding that "prenatal exposure to testosterone affects the development of the nervous system." Studies of rats, he says, reveal that offspring of older mothers have lower testosterone levels, and that male offspring have smaller reproductive organs (additional evidence of lowered testosterone).
"It may therefore be possible," he says, "that epidemiological changes in crime rates are not only based on changing social conditions but partly also on shifts in perinatal biological circumstances."
"Recent decreasing trend in U.S. juvenile delinquency attributable to changes in maternal age," Jacob F. Orlebeke, Psychological Reports, 2001, Vol. 88, 399-402. Address: Jacob Orlebeke, Vrije Universiteit, Department of Biological Psychology, Van der Boechorststraat 1, 1081 BT Amsterdam, The Netherlands, JF.Orlebeke@psy.vu.nl.