Scientific Study of Genes’ Effect on Behavior

Here’s an excerpt from yesterday’s Washington Post article by Rick Weiss on the use of DNA evidence in court for reasons other than identification:

. . . [W]hat of the murderers, rapists and other violent criminals who fall outside those narrow bounds? Can some, at least, blame their behavior on their genes?

Studies have shown that up to 62 percent of antisocial and criminal behavior is “heritable,” a rough measure of a genetic contribution. And in a few cases, courts have allowed arguments seemingly akin to “My genes made me do it.”

Weiss discusses several cases in which defendants have sought to have juries consider genetic predispositions to depression, mental illness, and violent behavior.

In discussing “[w]hether evidence of an inborn penchant for violence can be relied upon to evoke a jury’s sympathies”, Weiss writes:

[I]n a rare case in which a court did accept evidence of a defendant’s inborn “propensity to commit murder,” that court, in Idaho, considered it an aggravating factor, not a mitigating one, and used it to help justify the death sentence.

Such decisions are worrisome, said Markus Heilig, a research psychiatrist and neurochemist at the National Institute on Alcohol Abuse and Alcoholism. “To argue that behavior can be predicted, you are arguing this guy does not have free will,” Heilig said. “So how can you hold someone accountable?”

Not everyone goes that far.

“Just because you can explain a behavior’s cause doesn’t mean it is excusable,” said Nita Farahany, an expert in behavioral genetics and the law at Vanderbilt University.

Heilig and Farahany are clearly speaking different languages; they’re both correct.

A genetic predisposition to violence is a double-edged sword. It reduces a person’s moral blameworthiness (whether he can be held accountable) while making it more likely that the person will be a danger in the future; retribution becomes a smaller punishment factor but specific deterrence and incapacitation become greater ones.

New York criminal-defense lawyer Scott Greenfield asks “where to draw the DNA line”. He’s talking about the use of DNA databases to find family relationships between questioned DNA samples and known DNA samples. Consider Scott’s question in light of advances that are starting to allow scientists not only to match questioned DNA with known DNA, but also to identify those DNA donors who are more likely some day to commit crimes.

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0 responses to “Scientific Study of Genes’ Effect on Behavior”

  1. The interesting thing about all this is how uncomfortable people are with the concept of genetics as a basis for behavior. I’ve read probably about 1/3 of Steven Pinker’s The Blank Slate and he raises that issue a lot.

  2. Don’t you think it will be a very very long time before DNA is that specific? You are going to have to isolate violence genes and I don’t think that will happen in my lifetime.

  3. Ron, anything that smacks of determinism makes people uncomfortable. We’re so used to feeling that we exercise free will, that any suggestion that it might be an illusion is hard to accept.

    Jigmeister, to the contrary, we’re there now. See the third page of the article (free registration required):

    [A] number of studies have strengthened the link between MAO-A and violent behavior, and other genes have been added to the mix. This month, scientists in Israel reported that a version of a gene called AVPR1a is associated with “ruthlessness.” And although such tests can offer only the probability that a given behavior will arise, they can sway jurors, experts said, because they seem more scientific than a doctor’s clinical assessment.

    There is very little that I would dare say is not going to happen in my lifetime.

  4. there’s a wide gulf between statistically significant differences caused by the presence of certain genes and pre-determined behavior. the issue must become a rallying cry for defense lawyers and social advocates interested in a new paradigm of courtroom justice and, especially, correctional facilities based around mental health and deterrence. of course, this is still the same USA where large portions of society think that homosexuality is a choice, so really I think we’re pretty screwed.

  5. All I know is I don’t want them looking at MY genes!

    Colin, didn’t you contradict yourself? I agreed with your first statement but then you seemed to suggest exactly the opposite, (sarcastically) in your last. Sounds like a conundrum to me: DON’T gene-type my client as a murderer, but DO accept that we have no control over our sexual preferences!

    [Foul! Undefined use of the l-word. Your penalty is comment moderation until further notice. M.]

  6. there is no contradiction, though there are two different points to be found. the reference to homosexuality was me referencing my belief that most people are very ignorant about science and probability. they seem more interested in re-affirming their own beliefs based on scant evidence.

    maybe every homosexual has a certain genotype. maybe every murderer has a certain genotype. I concede that both are entirely within the realm of possibility. but the likelihood that a person with the genotype will display the associated characteristic is still undetermined. without a very high likelihood, using it as evidence in proving a criminal case when you have juries who [often] love to convict and probably won’t understand the science seems incredibly dangerous. in the contest of the probative and prejudicial, such evidence is incredibly suspect and I would expect courts to throw it out.

    on the other hand, it makes tremendous sense to use such knowledge as part of a treatment and deterrence program. use it to identify those prisoners who are most likely to re-offend and offer them specialized treatments. a world of possibility opens up of ways to re-engage a population that is otherwise highly dangerous and is likely to remain locked away for the rest of their lives.

  7. Seems reasonable in principle, Colin, but that last paragraphs sounds a little Clockwork Orangish!

    Mark: What’s the “I-word”?

  8. you’re worried that if we de-claw psychopaths that they won’t be able to survive in the wild anymore? or maybe there was some other message to that movie that I’m missing. last time I saw it was a few years ago.

  9. Man, where are the liberatarians on this blog when you need them? Can it be possible that it’s up to an authoritarian like me to carry their standard?

    If I’m not mistaken, the INTENDED message of “A Clockwork Orange” (which I haven’t seen in quite a while, either) was that the “cure” offered for violent thugs like Alex was, in its own way, every bit as disturbing as the problem it sought to eradicate.

    No sympathy for psychopaths here, I’m just applying the Holmesian “Bad Man” standard to your statement about “treatment and deterrence” and wondering how that idea could be extrapolated by governments inclined to misuse it. Sheesh — listen to me! Where are Mark and PJ? Please save me from this anti-authoritarian fever!

  10. As a fiction writer and a genealogist, I find your discussion very enlightening. This makes the study of family ancestry and nature/nurture so compelling.

    Nature and nurture are illuminated by each other. One’s environment determines behavior. One’s biology determines behavior. The two forces are inextricably bound together.

    The real question to ask, then, is not is it nature versus nurture, but rather, to what degree do the factors of nature and nurture influence behaviors? And how do those choices take form? You could choose to be a soldier to serve your country. And then your brother, brought up with those same military stories, might choose to write a patriotic song for his country. No one could deny both are patriotic acts, but they are very different responses.

    There is much to learn about the relationship between biology and environment.

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