The DNA Defense

Science, technology, and life.
April 24 2008 8:57 AM

The DNA Defense

In Sunday's Washington Post , Rick Weiss detailed an important and underreported trend: the increasing role of genetics in legal disputes . His reporting illustrates how the march of science and the evolution of law are changing the way we think of ourselves. In South Carolina, the state's highest court overturned a murder conviction based on evidence that the killer acted out of genetically based depression. In Tennessee, a murder defendant blamed his conduct on inherited mental illness. In Georgia, lawyers in a murder case sought tests to determine whether their client had a gene associated with violence. In Arizona, a convicted killer argued on appeal that his attorney should have told the court about a similar gene-based propensity.

William Saletan William Saletan

Will Saletan writes about politics, science, technology, and other stuff for Slate. He’s the author of Bearing Right.

How did we get here? Weiss's research suggests a confluence of two trends. One is the habituation of courts to DNA. The growing familiarity of this kind of evidence masks the evolving purposes to which it has been put. First came DNA as identification, basic CSI stuff. Then came DNA as evidence of harm: Plaintiffs sued companies over toxic damage, but their DNA failed to show the toxin's expected effects. Then there's DNA as a cause of disease: In pollution and malpractice cases, courts have tested plaintiffs' DNA to check out the argument that genes, not products or procedures, sickened them. And if DNA explains the past, why not use it to predict the future? HIV tests have already been court-ordered to project victims' longevity and thereby calculate lifelong damages. Genetic longevity tests will be next. In a custody case, one parent successfully demanded that the other be tested for the deadly Huntington's gene. Apparently, the point was to challenge the second parent's fitness.


So, we're already in the business of testing for genes to predict fitness. That brings us to the second trend: the increasing use of biology to assess criminal responsibility. U.S. case law has traditionally discounted perpetrators' culpability in the event of sleepwalking, epileptic seizures, insanity, retardation, or "diminished capacity." Three years ago, the Supreme Court struck down death sentences for teenagers, citing evidence of their " underdeveloped sense of responsibility ." Every month, scientists find new correlations between genes and traits such as aggression or mental illness . Just two weeks ago, the Human Nature News roundup flagged a study showing a genetic correlate of ruthlessness . As the cost of genetic testing declines, the temptation to test defendants increases. The persuasiveness of some genes increases as well: The allele cited in the Georgia murder case has subsequently been connected to violence in additional studies.

Put the two trends together, and you're looking at a gradual invasion of personal responsibility by genetic determinism. It's a conceptual shift from thinking of people as subjects to thinking of them as objects. The shift helps defense lawyers who need excuses for their clients' behavior. But it comes at a price: If your client is an object, why should we treat him like a subject?

As Weiss points out, courts already use unscientific evidence of "future dangerousness" to decide which killers should be executed. Genes could hardly do worse at predicting such risks. Weiss cites an Idaho case in which the defendant's genetic "propensity to commit murder" became a justification for executing him. A judge in the Arizona murder case drew the same conclusion about the appellant's "alleged genetic predisposition for violence." If your client's genes made him kill, they'll do it again. So don't expect us to let him live.

Nor should you expect us to protect his DNA from scrutiny under the Fourth or Fifth Amendment. If he's the product of his genes, as opposed to their manager, why should we treat them as his possession? He's their possession. Ditto for self-incrimination: If mental states are products of genes, we don't need his testimony; we just need his DNA. We can't make him open his mouth to testify, but we can make him open it for a swab, which could tell us plenty about his mind.

Are we more than our programming? Ladies and gentlemen of the jury, I leave that question in your hands .



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