Do people choose to commit crimes, or does biology push them toward it? That has been the question on the table for the last two decades when it comes to understanding how to punish criminal behavior in the face of genetic evidence.

The U.S. legal system, if it’s ever expected to work properly, depends on autonomy. People who commit crimes are only deemed culpable if a judge decides they had the mental clarity to understand their actions, and decided to do it anyway. But decision isn’t black and white, science is increasingly finding, particularly as the field of behavioral genetics uncovers the uncomfortable fact that what we do is often an indirect result of our biological predispositions.

A new report published in the journal Neuron seeks to illuminate the darker parts of that dilemma. Essay author Dr. Paul Appelbaum, director of Columbia University’s Center for Research on Ethical, Legal & Social Implications of Psychiatric, Neurologic & Behavioral Genetics, points out that while death penalty charges are the most common cases where mental illness and other genetic predisposition (such as toward substance abuse) are invoked, genetics actually finds a home in many civil cases, too. Employers protecting themselves against worker injury is one example.

“Employers contesting work-related mental disability claims might…want to compel claimants to undergo genetic testing to prove that an underlying disorder was not responsible for their impairment,” Appelbaum noted. Similarly, parents going through divorce proceedings may request psychiatric evaluation to determine one another’s fitness as a sole parent. Victims of auto accidents may want to seek data on the drivers’ predisposition to impulsive behavior.

Of course, high-profile criminal cases invoke genetics the most. Defense attorneys turn to the well-worn plea of insanity — to lift the burden of responsibility from their clients entirely, or at least to turn a death sentence into a life sentence. The challenge, as many courts see it, is wading through irrelevant information to arrive at the genetics that matter. Complicating that is the fact conscious and unconscious processes fall on a spectrum.

"People don't have the degree of control over their behavior that we thought," Deborah Denno, professor at the Fordham University School of Law, told Newsweek. "That doesn't mean to suggest that there's no control over their behavior — but that some of us have higher hurdles than others."

While geneticists are hard at work finding out what makes us tick, Appelbaum prescribes extreme care when dealing with these fragile cases. Genetics is a complex beast, yet our understanding of how decisions are made, and importantly, why they’re made, is rudimentary at best.

So far, the best scientists can do is offer up the evidence they do have. These come in the form of brain scans and hard genetic data. At best, judges have more information at their disposal, which they can use to inform their decisions. At worst, knowledge gaps let dangerous criminals slip through the system.

"The complexity of genetic information and our incomplete understanding of the roots of behavior raise the possibility that genetic evidence will be misused or misunderstood,” Appelbaum said in a statement. “Hence, care is needed in evaluating the extent to which genetic evidence may have something to add to legal proceedings in a given case."

Source: Appelbaum P. The Double Helix Takes the Witness Stand: Behavioral and Neuropsychiatric Genetics in Court. Neuron. 2014.