Is that a gun in your genes or are you just opportunistic?

A new U.S. study suggests the line between a life of crime and an honest existence could have more to do with your genetic makeup than your environment.

Researchers from University of Texas, Florida State University and Sam Houston State University were looking to determine the role genetic makeup has in someone becoming a "life-course persistent offender" -- characterized by antisocial behavior during childhood that can progress to violence or other serious crimes.

They looked at 4,000 subjects with three different behavioural paths: life-long offenders, those who experimented with crime (often substance use and minor property offences) in adolescence and those who stayed on the straight-and-narrow. They found genetic makeup influences life-course offenders by about 20 per cent more than it influences temporary teen troublemakers.

"The overarching conclusions were that genetic influences in life-course persistent offending were larger than environmental influences," said Dr. J. C. Barnes, criminologist at the University of Texas and co-author of a paper on the study published in a recent issue of Criminology.

"For abstainers, it was roughly an equal split: genetic factors played a large role and so too did the environment. For adolescent-limited offenders, the environment appeared to be most important," Barnes said in a news release.

Their analysis did not identify the specific genes that might lead people down different paths.

"There are likely to be hundreds, if not thousands, of genes that will incrementally increase your likelihood of being involved in a crime even if it only ratchets that probability by one per cent," Barnes said. "It still is a genetic effect. And it's still important."

The issue of using genes to predict a person's behaviour is not without significant controversy, which Barnes noted in his paper.

After reading some promotional material on the study, University of Guelph's Joe Colasanti -- an associate professor of molecular biology and genetics -- pointed out it fails to consider the unique situations behind each crime.

"Researchers have to be extremely careful when trying to connect genetic factors to behavioural traits," he told CTVNews.ca in an email. "There are so many things to consider, i.e. What defines a criminal? How desperate does a person have to be to commit a crime? How many abstainers would commit crimes if they were subjected to desperate situations?

"I can't comment on whether they have controlled for these factors, but frankly I can't see how they could."

The paper also doesn't appear to account for epigenetics, an area of study that shows gene behaviour can be altered without changing the genes themselves.

"There is increasing evidence that exposure to environmental conditions during early development (in utero) can affect behaviour later in life," Colasanti said. "So that is something else that these researchers might keep in mind."