The Supreme Court heard oral arguments last week in Roper v. Simmons, a Missouri case that raises the question of whether the Eighth Amendment's ban on "cruel and unusual punishment" forbids the execution of murderers who were 16 or 17 at the time they committed their crimes.
  
   The court was supposed to have settled this issue 15 years ago. In the 1989 case of Stanford v. Kentucky, a 5-4 majority found that there was no American consensus against the use of capital punishment in such instances, and ruled accordingly that the constitutional standard -- "cruel and unusual" -- didn't apply. On that score, not much has changed. Of the 39 states that have the death penalty today, half continue to permit the execution of murderers who were under 18 at the time of the killing. (No state allows the death sentence for murderers who were younger than 16, and every killer put to death in modern times has been at least 23 at the time he was executed.)
  
   But now the justices are being urged to overturn Stanford on supposedly scientific grounds. We know more than we used to about the way the adolescent mind works, the argument runs, and there are biological reasons why teens younger than 18 tend not to be as adept as adults in controlling their impulses.
  
   A friend-of-the-court brief filed by a gaggle of health-care organizations, including the American Medical Association and the American Academy of Child and Adolescent Psychiatry, claims that 16- and 17-year-olds behave differently than adults because their brains are not fully developed. To execute persons who commit murder at that age would be "to hold them accountable . . . for the immaturity of their neural anatomy and psychological development."
  
   A similar amicus brief, this one from the American Psychological Association and its Missouri affiliate, informs the court that "late adolescents are less likely to consider alternative courses of action, understand the perspective of others, and restrain impulses," since their "brain has not reached adult maturity, particularly in the frontal lobes." Tossing off references to "longitudinal MRI studies" and "cognitive neurology," the brief asserts that "16- and 17-year-olds as a group are less mature developmentally than adults." Well, stop the presses.
  
   The problem here is that what is relevant isn't exactly new -- what parent doesn't know that adolescents don't always restrain their impulses? -- and what is new may not be legally relevant. The work of UCLA neurologist Elizabeth Sowell is prominently cited in both of these briefs, yet Sowell herself warns against using neuroscience to promote a legal agenda.
  
   "The scientific data aren't ready to be used by the judicial system," she told Science News in April. "The hardest thing . . . is to bring brain research into real-life contexts."
  
   Skeptical, too, is Harvard psychologist Jerome Kagan, the former director of the Mind/Brain Behavior Interfaculty Initiative. "The brain data don't show that adolescents typically have reduced legal culpability for crimes," he says. Clearly teens "can control their impulses without having fully developed frontal lobes" -- otherwise "we should be having Columbine incidents every week."
  
   But we don't have Columbine incidents every week. The vast majority of 17-year-olds, like the vast majority of people at every age, don't commit violent crimes -- least of all the very worst violent crimes: the especially depraved homicides that the law calls capital murder. Adolescents who have not yet turned 18 may not always act wisely, but rarely do they turn to murder. Should those who do be regarded primarily as heedless kids -- or as determined killers?
  
   Consider Christopher Simmons, the defendant in the case before the Supreme Court.
  
   In September 1993, Simmons discussed with friends the crime he intended to commit: a victim would be robbed, then tied up and pushed off a bridge. On Sept. 8, Shirley Crook became that victim. Simmons and two friends broke into her home at 2 a.m., bound and gagged her with duct tape, then forced her into a minivan. Simmons drove the van to a railroad trestle spanning the Meramec River, where he found that she had managed to work some of the duct tape off. So he hog-tied her with electrical wire, then covered her face with even more duct tape. And then he threw into the river below.
  
   Simmons's age wasn't ignored in his trial. It was offered as a mitigating circumstance, and the jury took it into account when deciding his punishment. That is what the Supreme Court should continue to permit every jury to do.
  
   There are times when a bright-line rule based on age makes sense. We don't let kids drive until they are 16, or buy tobacco before turning 18. When it comes to drivers' licenses and cigarettes, an arbitrary cut-off is both reasonable and efficient.
  
   But when someone has been brutally murdered and an accused killer is in the dock, reasonableness and efficiency are not the standards we use. Guilt must be proven beyond a reasonable doubt. Jurors must weigh all the evidence. Criminal justice is done individually, particularly, with a focus not on how people act generally, but on how *this* person acted in *this* specific case.
  
   The law as it exists now does not condemn every 16- or 17-year-old murderer to death. It simply preserves capital punishment as one option for the jury. It allows society to say, in rare but appropriate cases, that a juvenile who plotted like an adult and murdered like an adult can be punished like an adult. That isn't cruel and unusual. It's justice.      
  

 

(Jeff Jacoby is a columnist for The Boston Globe.)