Apple’s new TV show reconsiders the ‘murder gene.’ Here’s what the science says

The following story contains spoilers from the third episode of “Defending Jacob,� “Poker Faces.�

Apple TV+’s limited series “Defending Jacob� stars Chris Evans as Andy, a respected assistant district attorney whose son, Jacob (Jaeden Martell), is accused of murder. In the third episode, Andy reveals that his own father killed someone, and is currently serving a life sentence in prison.

“That’s not who you are,� Andy tells Jacob. “He’s one guy, one bad man. He has nothing to do with you.�

But Jacob’s mother, Laurie (Michelle Dockery), disagrees. She remembers that Jacob was a difficult child who screamed constantly, threw things and often played too rough with classmates. One girl needed stitches after he pushed her off a play structure.

Those watching at home might wonder whether Jacob’s ancestry could complicate — or even determine — his future. It’s a nature-versus-nurture debate: Are certain people genetically predisposed to committing acts of violence?

“I’m certainly not looking to educate anyone about genetics, but hopefully this idea is another facet of the story,� series writer and creator Mark Bomback told The Times. “This show is, really, about raising children: whether or not you can ever really know them, and to what extent can someone be destined or not destined to act in certain ways, independent of how they’ve been parented over the years.�

Author William Landay first explored the subject in his 2012 book, on which the show is based. He was intrigued by a 1997 magazine article about three generations of men: a convicted grandfather, a cop father and a murder-suspect son, the latter of whom declared, “I was born with the murder gene.�

“That comment, at the time, had no scientific meaning at all, he was just using it as a shorthand to say that he had inherited a violent streak,� said Landay, who read publicly available research then emerging on behavioral genetics and neurocriminology and found it narratively compelling.

“As a writer, the idea that genetic destiny can override free will — that somebody might think, ‘Well, I can’t be blamed for my actions, because it’s in my genes’ — is haunting.�

Regardless of Jacob’s genome, does such a thing as a “murder gene� actually exist? While some criminal attorneys and works of fiction (including a past “Riverdale� episode) would argue otherwise, “there is no such thing as a ‘murder gene,’� said Dr. Carrie Bearden, professor at UCLA’s Department of Psychiatry & Biobehavioral Sciences.

“It’s not like Huntington’s disease, where there’s a single gene that causes the disorder, and you can do a genetic test to find if a person has that specific mutation and will, at some point, develop those symptoms,� she explained. “There’s no single, deterministic gene that would make someone commit a murder.�

There are, however, various genetic factors — linked to psychopathy, neuroticism, impulsivity, manipulating others, and a limited capacity for empathy — that can make someone more susceptible to commit a violent act, said Bearden. Though their heritability varies, the traits, if already present in the DNA, are more likely to be expressed if the person suffers abuse in their earliest years.

This is the science that “Defending Jacob� explores, as later episodes see the teenager completing emotional intelligence tests, brain scans and DNA tests. They’re all conducted by Dr. Elizabeth Vogel (played by Poorna Jagannathan), a biological psychologist whose specialty is genetic inheritance in behavior.

“Anyone looking to get these kind of answers would have to be personally examined by a psychologist or psychiatrist who is an expert in your age group and personality disorders,� said James Fallon, professor of psychiatry and human behavior, and emeritus professor of anatomy and neurobiology, at the UC Irvine School of Medicine, who served as a consultant on “Defending Jacob.�

He urged Bomback not to oversimplify the facts, as other films and TV shows have done. Why? “Even if it turns out that you randomly inherited a certain mixture of these genes, that doesn’t mean you’re going to turn out to be a serial killer,� said Fallon. “People always think it’s diagnostic, but they’re more like warning signs. It doesn’t determine your whole life.�

Viewers will have to stay tuned to find out how Jacob’s test results will play into his fate — either in revealing whether he was more likely to have committed the crime, or in swaying a jury to believe he may have done so anyway, even if he’s innocent.

Landay hopes those tuning in do so with a grain of salt. “The science is genuine, with very little changes made, but I caution against reading this novel or watching this series as a scientific document of what this idea of a ‘murder gene’ might mean,� he said.

“It’s important that, in both literature and in law, we understand that there is no ‘murder gene’ in the sense that that you could have a predetermined genetic destiny and no sense of self-direction,� he continued. “We all control our instincts and our emotions all the time. We are much more than the sum of our genetic code.�