Instead, Shaquille — who spoke on condition that his full name not be used, lest his record jeopardize his chances of finding a job — wound up in San Francisco’s Young Adult Court, which offered him an alternative.
For about a year, he would go to the court weekly to check in with Judge Bruce E. Chan. Court administrators would coordinate employment, housing and education support for him. He would attend weekly therapy sessions and life-skills classes.
In return, he would avoid trial and, on successful completion of the program, the felony charge would be reduced to a misdemeanor. This was important, because a felony record would make it nearly impossible for him to get a job.
“These are transitional-age youth,” said Carole McKindley-Alvarez, who oversees case management for the court. “They’re supposed to make some kind of screwed-up choices. We all did. That’s how you learn.”
Surprisingly, this alternative legal philosophy springs not from concerns about overcrowded prisons or overburdened courts, but from neuroscience.
Researchers have long known that the adolescent brain is continually rewiring itself, making new connections and pruning unnecessary neurons as it matures. Only recently has it become clear that the process stretches well into early adulthood.
Buried in that research is an uncomfortable legal question: If their brains have not fully matured, how responsible are adults ages 18 to 24 for their crimes?
Should they be treated more like adolescents, handled in the comparatively lenient juvenile system, or more like hardened 35-year-olds? Should young adults be held fully responsible for certain crimes but not others?
After attending a lecture at Harvard on brain development, George Gascón, the San Francisco district attorney, decided to tackle these questions head on. In 2015, he and Wendy Still, then the city’s probation chief, established Young Adult Court, a hybrid of the adult and juvenile justice systems tailored to the biology and circumstances of offenders 18 to 24.
Mr. Gascón and his colleagues argue that neurological immaturity may contribute to criminal behavior. Adult sentences constitute cruel and unusual punishment, they say, and undermine the possibility of rehabilitation.
Trained by a clinical psychologist in recent neuroscience, members of the court’s staff are trying to apply the scientific findings to prevent lifelong entanglement with the criminal justice system.
“It’s an opportunity demographic, is what it is,” Judge Chan said. “This is a really malleable group of people with tremendous capacity to change.”
The Developing Brain
For most of the past century, scientists assumed brains were fully developed by age 18. Then, in 1999, Dr. Jay N. Giedd of the National Institute of Mental Health published a study in Nature Neuroscience that challenged this view.
He used M.R.I. scans to track the brain development of 145 people ages 4 to 22. The study was intended to explore structural changes during the transition from childhood to adolescence, but Dr. Giedd found that neural connections continued to be refined well past age 18.
Over the next decade, other researchers confirmed that the brain seems to undergo a burst of growth and connectivity after age 18, but few experts pursued those observations. In 2012, a comprehensive analysis of brain development omitted data on young adults ages 18 to 21 because so few studies had been done.
But if neuroscientists were not interested in the implications, legal scholars were. A series of Supreme Court rulings — most notably Roper v. Simmons in 2005, which abolished the death penalty for juveniles — was partly based on science suggesting that adolescent brains are not fully developed. This continuing process, the justices reasoned, diminished culpability and justified sentencing that was less harsh.
Laurence Steinberg, a psychologist at Temple University, set out to determine when exactly an adolescent becomes an adult.
Dr. Steinberg gave psychological tasks to 935 people ages 10 to 30 to distinguish between cognitive capacity and “psychosocial maturity.” His team reported that people performed as well as older adults on cognitive tasks — such as recalling 13-digit numbers forward and backward — by age 16.
Yet psychosocial maturity — measured by impulsivity, risk perception, thrill-seeking, resistance to peer influence — did not begin until age 18, gathering momentum through the early 20s.
“It appeared that these two traits might develop on different timelines,” Dr. Steinberg said.
In 2011, the MacArthur Foundation organized a group of legal scholars and scientists, including Dr. Steinberg, to study criminal justice and young-adult brains in more detail. It was no secret that the criminal justice system’s approach to young adults was not working.
Young adults 18 to 24 make up 10 percent of the population, but they account for 28 percent of all arrests (2.1 million in 2015), a rate higher than that of any other age group.
Arrest rates are particularly high among minority males: Nationally, about half of all black men have been arrested by age 23.
Convictions at this age often are the harbingers of derailed lives: 84 percent of young adults released from prison will be rearrested within five years. Few with felony convictions will be able to find jobs.
A court informed by biological research could play a role in bringing down those numbers, Mr. Gascón hopes, even if most of these offenders face considerable economic and racial barriers.