As investigators try to unravel the possible motives of the Boston marathon bombing suspects, brothers Tamerlan Tsarnaev, 26, and Dzhokhar Tsarnaev, 19, factors like their Chechen background, Muslim faith and family histories are being dissected.
But their age and gender are perhaps so obvious, we don’t consider them as factors.
"I'm currently at a child development conference and here, if you'd gone up to anybody, even before they knew a single thing [about the suspects] and asked them who did this? They'd all say: Male in his 20s," said Laurence Steinberg, Ph.D., professor of psychology at Temple University.
Adam Lanza, Seung-Hui Cho, Dylan Klebold, Eric Harris, Timothy McVeigh, Marc Lￃﾩpine are all young men responsible for mass killings. One study estimated that 98 percent of mass killings in the U.S. are carried out by men, but some experts say a killer’s age profile is also predictable.
"In all my research, every multiple death act of violence has been perpetrated by one to two male adolescents," said Abigail A. Baird, Ph.D., an associate professor of psychology at Vassar College who studies the age group. "I'm not comfortable saying that's a coincidence."
No one suggests that most young men are dangerous, just that people who do inflict mass violence are young men. And understanding why young women and older people do not express their aggression, despair or illness in this way may help explain one part of what fuels these attacks.
"A decade ago, you’d read articles suggesting that adolescents engage in high-risk behavior because the prefrontal cortex was not fully developed,” B.J. Casey, Ph.D., director of the Sackler Institute for Developmental Psychobiology at Weill Medical College of Cornell University, said in an interview with The Dana Foundation. “But it is even less developed in children who don’t engage in such behavior. We now think more in terms of neural circuitry; how regions of the brain talk to one another.”
Decision-making, like all brain functions, relies on a series of neural circuits, missives from different areas of the brain, conspiring to execute a function. It is the opinion of researchers that the neural circuitry of adolescents, or those between 18 to 26, simply light up different pathways. The young adult brain is primed for better learning and adaptation, but it also favors sensory reward and immediacy over long-view thinking.
For example, although many terrorists commit their crimes alone, acting together -- as the Tsarnaev brothers are accused of doing -- can have its own neurobiological effect. The company of others lights up the reward pathways of the young adult brain in a way it does not for older people, according to the research, dwarfing their perception of risk. In other words, the excitement of action and of social bonding loom large over the potential consequences.
Overall, young men are risk takers, sensation-seekers and eager to prove their masculinity, according to Steinberg. They are the demographic most likely to die from accidental injury. They tend to have higher average car insurance premiums because actuaries know that members of this age group are more likely to drive recklessly, to have a fatal car crash and to drive under the influence of alcohol or drugs. They are more likely to abuse drugs and to break the law.
"If you look at crime data, you find what's called the age-crime curve," said Steinberg. "It's flat until about age 10 and then it peaks at about 18. What's amazing about this is that it transcends all cultures -- it's the same in all countries. And it's very robust over historical data too. If you look at different time periods, you'll find different average levels of crime, but the same distribution."
Those in that age range are at the peak of a variety of neurochemical phenomena, said Baird. "You build muscle easiest, you are more able to stay awake at night, you're less sensitive to punishment, more focused on status and reward," she said. "That doesn't mean you'll be violent -- it also could mean you'll be the opposite: Firefighters and law enforcement are also mostly young men. It's also the thing that allows you to run toward an explosion."
Young men experience a surge of testosterone that leads to an impulse to prove oneself, Baird explained. Testosterone means you’ll want to increase your status and many young men seek status as the toughest, the most popular and -- if they display antisocial thinking -- the most aggressive and violent.
Female counterparts also take greater risks, act impulsively and can be more aggressive during young adulthood, but they are more likely to be reined in by social expectations. According to Baird, the fact that the rates of arrest for assault among girls are rising at a greater pace than for boys is alarming because schoolyard fights among girls are viewed as non-normative behavior.
What’s more, young women are more likely to heed social cues, Baird explained. They are more likely to fear ostracism and to feel the disapproval of others. Where girls are neurologically primed to build coalitions, to foster relationships and a tight-knit social group, boys are primed to assert dominance and to stand out.
Young people also are more responsive and reactive to stress during this time in development. "No one understands the biological mechanism, we just know that it is more likely for things to become derailed during this time," said Steinberg. "It's not a coincidence that these years are the major points of time at which addictive disorders begin to manifest, [and] people first show signs of serious depression and schizophrenia."
Mental illness doesn't cause this type of violence, experts point out, but they are temporally correlated. Young adulthood is a trying time, culturally, and it may be that young adults are uniquely, biologically ill-equipped to handle the stressors.
There is no doubt that anyone behind the Boston bombing is deeply pathological -- anyone who intends to harm others has to be -- but that pathology combined with other possible factors like social dissatisfaction, expectations of masculinity, the biology of poor stress response and increased impulsivity, could create a perfect storm.
“There are some studies underway to see if we can improve people's self-control during [young adulthood], but we don't have any answers yet,” said Steinberg.
Baird was less hopeful. "It feels like we could have stopped [the attack] because it was carried out by humans," she said. "But really it's as random as a bus accident."