NBC -- "I liked the violence, kind of the drama of it. I liked fighting. I liked it. I loved it. I fed off of it," Mr. C said.
To protect his identity, we'll call this former gang member Mr. C.
Though he was in gangs for eight years, he now works with Salt Lake County's project 180, to help persuade young people to walk a different path.
We don't know whether 'C' was genetically predisposed to join a gang, but Dr. Kevin Beaver's study at Florida State University's College of Criminology and Criminal Justice found a link in a lot of other gang members.
"In short, what we found was that the gene predicted membership into a gang. It also predicted weapon use in a general population; and then among gang members, it predicted those gang members who were the most violent," Dr. Beaver said.
Nearly half of our 23-thousand genes are expressed in the brain and potentially affect behavior.
Researchers have long known the MAOA gene helps process dopamine and serotonin - two chemicals that influence behavior.
But many males get a variant of this enzyme, sometimes dubbed the warrior gene, which may play an even stronger role.
Males may be more vulnerable because they get only one MAOA gene on their one x chromosome.
Females get two since they have two x chromosomes. One theory suggests the second MAOA may diffuse the effects of the other, if it is a warrior gene.
"But there are a number of studies that suggest that MAOA variations, in particular under certain circumstances, can increase risk of anti-social behavior," Dr. Lynn Jorde, a geneticist, said.
If true, did Mr. "C" see the worst of this in his own gang?
"I mean the random acts of violence for God knows what purpose, just want to see pain - that's it - that's the only reason I could see that they would do what they did," he said.
But behavioral genes are only 50 percent of the recipe.
Jorde says not every male who gets a warrior gene will end up as a violent member of a gang.
How or where a boy grows up must be added to the mix.
"It's not just the gene, it's not just the environment, it's the interaction of the two," Dr. J. Dee Higley, a psychologist, said.
A Brigham Young University study shows where or how a boy is raised plays an equal role.
What J. Dee Higley and his colleagues found specifically? "Our study showed that individuals who grew up without their mothers tend to express the gene and it magnifies its effects," he said.
Family, the neighborhood, peers, child abuse, all can diffuse or activate the influence of the gene -- and as Florida State suggests, increase a boy's risk four fold to become a violent member of a gang.