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Genetic Linkage

The Crime Gene Revisited

"Research shows genes influence criminal behavior," proclaims a January 25 news release, setting my genetic determinism detector on high alert.

I flashed back to the cover of the May 18, 1970 Newsweek, “Congenital Criminals?” which probed the work of Patricia Jacobs. Here’s what my human genetics textbook says on the study provoking the 1970 headline:

“In 1965, researcher Patricia Jacobs published results of a survey among 197 inmates at Carstairs, a high-security prison in Scotland. Of twelve men with unusual chromosomes, seven had an extra Y.”

Press coverage exploded after the nefarious extra Y turned up in mental institutions. And so the “crime chromosome” became a legal defense and a Law and Order plot.

Fortunately, when in the early 1970s social workers and psychologists visited the homes of such doomed boys to offer “anticipatory guidance” to the anxious parents on how to tame their toddling Jeffrey Dahmers, geneticists halted the effort, predicting that the attention might trigger a self-fulfilling prophecy. The situation was a little like when Michael J. Fox’s character Marty McFly goes “Back to the Future” and spies his future criminal uncle behind the bars of a playpen.

Only a few of the 1 in 1,000 men who have an extra Y have associated characteristics: they’re tall and prone to acne and speech and reading problems. Might teachers with unrealistic expectations for boys who looked older than they were sparked frustration and perhaps aggression?

The Y chromosome story is a classic in genetics, a harbinger of today’s rampant genetic determinism (“It’s in her DNA!”). I suspected the new study, from criminologists J.C. Barnes at the University of Texas at Dallas, Kevin Beaver at Florida State University, and Brian Boutwell at Sam Houston State University and published in Criminology, was a genome-wide association study (GWAS) linking genetic markers with a life of crime. “Associating” genes to all sorts of behaviors is common these days. But their approach was a more traditional expansion of the “twin study.” If identical twins share a trait more often than do fraternal twins, the trait has a significant inherited component.

The criminologists investigated 3,000 or so sibling pairs with decreasing proportions of shared genomes: identical twins (100%), fraternal twins (50%), non-twin siblings (50%), half-siblings (25%), and for comparison, first cousins (12.5%). The participants are part of the National Longitudinal Study of Adolescent Health at the University of North Carolina, which is following a large cohort of kids who were in grades 7-12 during the 1994-5 school year. A “delinquency scale” reflected participants’ admission of such escalating behaviors as painting graffiti, lying to parents, running away, and stealing.

The new twist on the crime gene story is that the researchers also classified participants using a “developmental taxonomy” from 1993 that distinguishes “life-course persistents” (LCPs), who’ve been bad since childhood, from “adolescence-limited” (AL) people, who’ve behaved badly only as teens. (Another group is “abstainers,” but I can’t figure out whether that's equivalent to the geneticist’s “wild type” or normal. How does a sequence of DNA specify a sequence of amino acids that prevents someone from stealing a TV?)

The paper offers a statistical analysis, which is not, I’ll admit, my area of expertise. (Logarithms induce panic attacks.) The calculations estimate “heritability,” which refers to the contribution of genetics to the VARIABILITY of a trait – not to the trait itself, news release headline notwithstanding. And the researchers discovered mostly what they expected: the closer the relationship, the more alike the scores on the delinquency scale, except for the odd finding that cousins living in the same household were more alike, criminally speaking, than half-sibs, who share twice as many genes.

The conclusion: genetic factors explained 56-70% of the variance for lifelong criminals but only 35% for the teen-only type. This means teen-only criminals can blame the environment to a greater extent than can those who’ve lied, stolen, cheated and worse since childhood.

As I feared, the media zoomed in on the sexy news release headline that put “genes” and “criminal behavior” in the same sentence, although the study mentions nary an actual gene. And like the antiquated game of telephone, the message morphed in the headlines of articles and blogs:

“Life of crime is in the genes, study claims”

“Lifelong criminality may arise from genes”

“Genes could influence people to become criminal”

“Genes, Criminal Behavior Linked in University of Texas Study”

These simple conclusions based on fuzzy data from non-geneticists feed the genetic determinism mindset that we are our genes. And that can lead to making excuses for antisocial behavior, or losing hope of changing it, for if a trait is encoded in our DNA sequences, then we can’t control it.

The lead author indeed clarifies that there’s no gene for criminal behavior, but instead, many genes that may contribute slightly to raising the risk of committing a crime. But didn’t we already know this?

The one paragraph actually about genetics in this 32-page article is awkward and inaccurate. “With the recent mapping of the human genome, researchers are beginning to pull back the “heritability curtain” and identify links between measured genes and phenotypic outcomes. This line of research—referred to as molecular genetics—has already produced a wealth of knowledge.”

Not quite.

The first human gene was mapped in 1968, and the matching of genes to their chromosomes began in earnest in the 1980s; the criminologists are referring to the sequencing of the human genome, first drafted by 2000. Molecular genetics is looking at DNA, RNA, and protein sequences, not linking measured genes – sequenced genes? – to phenotypes.

But my concern is the hyped headline, which found its way into the media more than info from the report that's much more social science and statistics than genetics. Yet it’s the genetics that’s trumpeted. My worry is that the general public isn't given enough information to evaluate the findings, which really just restate the nature/nurture debate as applied to a life, or adolescence, of crime.

Marty McFly knew as much.

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