Princeton University criminologist John Dilulio calls them "superpredators."
They're the kids under eighteen who are thought to account for 25 percent of the
violent crime in our country. Between 1989 and 1994, arrests for violent crime
(murder, rape, robbery, or aggravated assault) rose 46.3 percent among fourteen-
to seventeen-year-olds, three to four times the increase observed in other age
groups. And although figures for 1995-1996 suggest that the violent crime rate
for juvenile offenders finally may have entered a downward trend, experts predict
that the worst is yet to come, when the 40 million children currently under age
ten reach adolescence in the inaugural years of the twenty-first century.
we contemplate the implication of these figures, however, we need consider one
final demographic detail. The faces of tomorrow's teenage killers belong overwhelmingly
to today's little boys.
Men are nine times more lethal than
women, and adolescent boys are already dangerous. Can it be mere coincidence
that this is the same time that escalating levels of male hormones flood the body
and the nervous system? Is puberty the culminating event in a hormonally driven
process of sexual differentiation that begins edging toward aggression even before
Studies in mice-a species in which prenatal hormonal
manipulations are performed unwittingly by siblings-highlight the organizational
role of sex hormones during brain development, an influence that will bias subsequent
endocrine responsiveness. Female mouse fetuses positioned in utero between two
males are exposed to more of their brothers' testosterone and less estrogen than
females who develop next to a sister. As pups, these "2M" females have
higher blood levels of testosterone; as adults, they boss other females and behave
even more aggressively following testosterone injections. Males who spend the
first weeks of their lives between two female fetuses, on the other hand, are
less responsive to testosterone as adults.
After birth, testosterone
continues to oversee the process of sexual differentiation that began in the womb.
Now hormones guide the first stages in the development of sexually specific behavior
patterns-in males, for example, the propensity to attack other males rather than
By the time mice and other rodents reach sexual maturity,
the weapons are in place. Exposure to testosterone during the critical period
of rapid brain development has titrated hormonal sensitivity and selected a battery
of sex-specific responses suitable for use in threatening circumstances. Puberty
finalizes mature patterns of social interaction: sexual advances toward females
and the stereotyped behavior patterns that characterize adult aggression toward
But now a second factor, context, begins to play an increasingly
important role. The outside world takes the male behavior pattern defined by testosterone,
a competence that might be called "aggressive efficacy;" and specifies
when, where, and how it should be used. As environmental information accumulates,
testosterone shares the responsibility for regulating aggressive behavior with
experience, acting as a facilitator and historian, not a dictator.
experiment by psychologists Renee Primus and Carol Kellogg, of the University
of Rochester, demonstrates how sexual maturity brings a new awareness of external
cues, linking testosterone, perception, and response. Female rats, paired with
a stranger in a familiar cage or a new, previously unexplored enclosure, were
equally sociable-sniffing, nudging, and grabbing-in both environments. Males,
on the other hand, were much more sensitive to their surroundings. Beginning at
puberty, male pairs placed in an unfamiliar cage tended to avoid one another,
while pairs confined to a familiar environment interacted far more frequently,
a difference prevented by castration at an early age. Testosterone, in other words,
did not simply release or drive social behavior, but governed the ability to match
key features of the environment with specific responses. A rat-or a human-who
cannot make such distinctions is guaranteed to do the wrong thing at the wrong
Testosterone levels in boys begin to surge at approximately
age ten, rise rapidly over the next several years, and finally begin to plateau
at about age fourteen, when aggressive behavior starts winding up. Coincidentally,
this is also an age of rapid social change. Peer group rankings shift daily, with
petty quarrels, athletic competitions, academic events, and girls offering ample
opportunities to win or lose face. Conflicts with parents and other adults mark
an urgent determination to muscle into the broader social structure, conflicts
with higher stakes and a greater risk of defeat. Testosterone, now available in
adult-strength doses, dutifully records each success or failure.
is it the rise in testosterone that causes violent behavior in adolescent boys?
Data collected over the past decade by psychologist Elizabeth Susman (currently
of Pennsylvania State University) and colleagues at NIMH and the National Institute
of Child Health and Human Development fail to support a relationship between antisocial
behavior, including aggression, and elevated testosterone levels; in fact, these
studies suggest just the opposite. Delinquent behavior, adjustment problems, and
rebelliousness in adolescent boys aged ten to fourteen were associated with lower,
not higher, testosterone levels. On the other hand, a Scandinavian study of fifty-eight
Swedish boys between the ages of fifteen and seventeen (the last stage of puberty)
did find a significant relationship between plasma testosterone levels and verbal,
as well as physical, aggression. The most interesting feature of this study, however,
was not what it said about the relationship between hormones and aggressive behavior,
but what it said about the relationship between hormones and perception. Testosterone
was most clearly linked to aggression when the violent behavior was a reaction
to an overture perceived as a threat. Boys with higher levels of testosterone
were more impatient and irritable, readily frustrated, and quick to take offense.
The tendency to start fights, rather than fight back, was less strongly correlated
with hormone levels. Testosterone, the report concluded, was less likely to drive
aggression than it was to magnify a boy's "readiness to respond vigorously
and assertively to threats and provocations."
perception involves neurotransmitters as well as hormones, in particular,
the norepinephrine-containing neurons of the locus ceruleus that form the central
branch of the global sympathetic response system. The power of this system lies
in its flexibility, in its aptitude for tailoring the level of arousal to the
level of risk posed by the environment. Each individual is born with an innate
sensitivity to environmental stimuli-some more reactive, others less so. But the
final working level of arousal is set by experience, by the nature of the interactions
between the child and the outside world. This postnatal maturation process is
reflected in the gradual development of the startle reflex.
a developmental point of view, the startle reflex goes through some major changes
in early childhood,"observes Robert Pynoos of the UCLA Neuropsychiatric Institute.
Confront adults with a sudden high-pitched tone, and they jump, Pynoos explains.
But warn them a fraction of a second earlier, and they're not so quick to startle.
Two-year-olds don't habituate this way. They react even more intensely to the
second stimulus, which, he notes, explains why his young daughter became more
and more frightened during her first fireworks display. The tendency to overreact
peaks between four and five years of age, then gradually declines.45 However,
reaction times don't fall to adult values until about age eight, just before pubertal
hormones kick in.
Pynoos points out that the evolution of the startle reflex coincides with developmental changes in self-defense strategies.
"If you put young children in a dangerous circumstance, they'll turn away
from the danger and seek out protection. But about age eight, you start to hear
the child fantasize about intervening actively: 'I wish I could have gotten the
gun away from him.' It's a precursor to adolescence, when kids make real decisions
about whether to intervene or not."
The hormonal changes
of puberty therefore collide head-on with the first mature responses of the
brain's alarm system, in the volatile context of an unstable social structure
and frequent clashes with authority. But what happens when the alarm system has
already been overloaded, when an abusive parent, daily exposure to a violent,
dangerous neighborhood, or repeated harassment by a troubled sibling have made
it clear that the world is a dangerous place? Pynoos and his colleague, Edward
Ornitz, analyzed startle reflexes in school-age children suffering from PTSD and
found that their startle responses failed to habituate (Figure 6.3). "Instead
of a ten-year-old pattern, their responses look like a five-year-old pattern,"
he says. As a result, these children continue to overreact to environmental cues,
their catecholamine hazard-detection systems placed on alert by trauma. Instead
of relying on adults to protect them, as a five-year-old might, they've got a
ten-year-old's determination to solve their own problems. Tragically, the result
can be an adult decision to use a gun.
Adolescence is a time when perceptual
and response patterns formed by years of interaction between brain and environment
are tested in adult society for the first time. 'When this process has gone well,
risk assessment will be accurate, the need to resort to violence minimal. When
it has gone poorly, gaps, misconceptions, and excesses will be clearly exposed-and
violence may well ensue. Hormones may be the most obvious biological event of
puberty, but adolescent violence, like adult violence, is more likely to be the
product of a brain that has developed a misguided notion of threat than a brain
fired up by testosterone.
- Niehoff PhD, Debra, The Biology of Violence; The
Free Press: New York, 1999
Reflection Exercise #8
The preceding section contained information
about whether testosterone is a factor in sex offending. Write three case study
examples regarding how you might use the content of this section in your practice.
What does Pynoos points out regarding the evolution of the startle
reflex? Record the letter of the correct answer the .