Is it all in the genes?

Increasingly, a person’s genetics are playing a role in court cases. You watch CSI and CourtTV. It’s all about DNA evidence.

But are we interpreting the information provided by the tests properly? Some statisticians and lawyers don’t think so.

Mathematics might seem a logical fit for the courts, then. Judges and juries, though, all too often rely on gut feeling. A startling example was the rape trial in 1996 of a British man, Dennis John Adams. Adams hadn’t been identified in a line-up and his girlfriend had provided an alibi. But his DNA was a 1 in 200 million match to semen from the crime scene – evidence seemingly so damning that any jury would be likely to convict him.

But what did that figure actually mean? Not, as courts and the press often assume, that there was only a 1 in 200 million chance that the semen belonged to someone other than Adams, making his innocence implausible.

It actually means there is a 1 in 200 million chance that the DNA of any random member of the public will match that found at the crime scene (see “The prosecutor’s fallacy”). The difference is subtle, but significant. In a population, say, of 10,000 men who could have committed the crime, there would be a 10,000 in 200 million, or 1 in 20,000, chance that someone else is a match too. That still doesn’t look good for Adams, but it’s not nearly as damning.

If all of my reading on rationality is teaching me something, it’s that in a lot of situations, human nature is all about jumping to conclusions. And when someone’s life or liberty is on the line, jumping to conclusions is a dangerous thing to do. I can’t think of a better time to sit back and analyze carefully and rationally what is going on. Go ahead and go with your gut on standardized tests, but turn on those higher functions when it comes to others’ futures or your own.

And then there’s the question of how much at person’s genetics influence his or her actions.

In 2007, Abdelmalek Bayout admitted to stabbing and killing a man and received a sentenced of 9 years and 2 months. Last week, Nature reported that Pier Valerio Reinotti, an appeal court judge in Trieste, Italy, cut Bayout’s sentence by a year after finding out he has gene variants linked to aggression.

Do genes remove or mediate personal responsibility? Where do arguments like this leave free will?

Read the article about Bayesian interpretation of statistics at New Scientist.

Read the article about genetic profiling at New Scientist.

How well can you forget?

I’ve been debating posting on this for a couple of days now. On one hand, the question of the reality and validity of repressed memories is interesting. On the other hand, we are talking about a man convicted of an awful crime that is related to a perhaps even more evil cover-up.

Remember Paul Shanley? The now-former priest who became the poster molester of the sex abuse in the Catholic church a few years ago? He’s now appealing his conviction. And he may have a good argument.

There were dozens of priests and hundreds of victims involved, but Shanley’s case is unusual in that there is no corroborating evidence of his crimes. Often in cases of accusations of sexual abuse — even ones that occurred years earlier — there is some other supporting proof. But the only evidence against Shanley was the memory of a now-grown man who said he didn’t recall the abuse until 2002 when he heard about a newspaper article on the clergy abuse scandal. That, he claimed, triggered a flood of memories of abuse that had occurred decades earlier at Shanley’s hand.

The problem? What the victim claims is unheard of in science.

Shanley’s lawyer argued that the former priest deserves a new trial because the jury relied on misleading “junk science” testimony about repressed memories, wrongly suggesting that such memories were considered valid by the psychological and scientific community. (Indeed, a judge concluded that repressed memories are “generally accepted by the relevant scientific community of mental health professionals.”)

Shanley’s lawyer is correct: There is no scientific consensus (and little research suggesting) that people can completely forget about traumatic events, only to recall them in detail years or decades later.

Dr. Elizabeth Loftus, for one, has spent her career studying the mechanisms of memory and how easily memories can be corrupted. Here’s her overview of the literature on creating memory, repressed memories, and the power of suggestion as of 2003.

It will be interesting to see how this plays out.

Even if this conviction is overturned, Shanley was accused of abuse by three others, who were dropped from the original suit.

Read the livescience.com column by Benjamin Radford.

Read the story at boston.com.