Sunday, 4 July 2010

Biology isn't destiny, but it affects your saving throws

James Fallon, UC Irvine neuroscientist, found he had the genetic predisposition for violent behaviour combined with ominous PET scan results:
Fallon says nobody in his family has real problems with those behaviors. But he wanted to be sure. Conveniently, he had everything he needed: Previously, he had persuaded 10 of his close relatives to submit to a PET brain scan and give a blood sample as part of a project to see whether his family had a risk for developing Alzheimer's disease.

After learning his violent family history, he examined the images and compared them with the brains of psychopaths. His wife's scan was normal. His mother: normal. His siblings: normal. His children: normal.

"And I took a look at my own PET scan and saw something disturbing that I did not talk about," he says.

What he didn't want to reveal was that his orbital cortex looks inactive.

"If you look at the PET scan, I look just like one of those killers."


Fallon calls up another slide on his computer. It has a list of family members' names, and next to them, the results of the genotyping. Everyone in his family has the low-aggression variant of the MAO-A gene, except for one person.

"You see that? I'm 100 percent. I have the pattern, the risky pattern," he says, then pauses. "In a sense, I'm a born killer."


Jim Fallon says he had a terrific childhood; he was doted on by his parents and had loving relationships with his brothers and sisters and entire extended family. Significantly, he says this journey through his brain has changed the way he thinks about nature and nurture. He once believed that genes and brain function could determine everything about us. But now he thinks his childhood may have made all the difference.

"We'll never know, but the way these patterns are looking in general population, had I been abused, we might not be sitting here today," he says.

As for the psychopaths he studies, Fallon feels some compassion for these people who, he says, got "a bad roll of the dice."

Discover comments here; Geeks are Sexy here.

I tend to think of these sorts of things in D&D terms. Fallon made his saving throw against a bad childhood, which meant he had a helpful adjustment to his save versus MAO-A, which he also made. Had he failed that throw, he would have had a strong penalty on willpower checks. If you know you have the propensity, you get an extra "self awareness" check that lets you evaluate whether your course of action really makes sense.

It will be interesting to see how this work plays out in court decisions over the next few decades. We can reasonably model folks with particular gene variants as having higher costs of avoiding illegal behaviour: their supply of illegal behaviour is more inelastic. So it will be more costly to deter them from engaging in any particular act. Recall Friedman's argument in Law's Order:
Net damage = damage to victim - gain to criminal.
For the marginal offence, the one that will be deterred if we raise the punishment just a little more,
Gain to criminal = expected punishment
Net damage = damage to victim - expected punishment.
For the optimal punishment,
Cost of deterring one more offense = Net damage = damage to victim - expected punishment.
Rearranging gives us
Expected punishment = damage to victim - cost of deterring one more offense,
or, in the more compact notation of mathematics,
(P) = D - MC
Suppose we have two groups of individuals sorted by genes: the first whose supply of criminal activity is relatively elastic, the second whose supply is relatively inelastic (warrior gene or other predispositions). A fixed penalty across both groups won't be efficient: it's cheap to deter the former and very expensive to deter the latter and so we'll be overpunishing some of the latter and underpunishing some of the former relative to an efficiency norm. If penalty schedules varied by genotype, we'd have harsher penalties for folks without the genetic predisposition to crime as their supply of criminal activity is elastic and lighter penalties for folks with the genetic predisposition. Yes, it takes a stronger penalty to deter the inelastic; but, because it's more expensive to deter folks with the higher crime genotype, we should spend less on deterring them, not more.

This of course leaves to one side the potential benefits of incapacitation, which could tilt things towards longer punishments for folks whose genetic predisposition makes it likely that they'd re-offend.

But, I rather expect that the political debate will be framed more around (US) liberals arguing for treatment programmes rather than jail for folks with genetic predispositions to crime (regardless of any evidence of effectiveness) and (US) conservatives arguing for harsher punishments for criminal monsters (regardless of whether the incapacitation benefits outweigh the higher deterrence costs).

Check also parts two and three of the NPR series. Part 3 suggests juries are finding the genetic evidence to be exculpatory rather than incriminating: murder turns to manslaughter.


  1. That whole "my PET scan looks like that of a psychopath" smacks of modern day phrenology :) He could have saved his rellies time and PET expense by noting he has the forebrow and eye shape of a criminal :D

  2. "I tend to think of these sorts of things in D&D terms." No surprises there :)
    I'd suggest maybe Dragonar might display similar characteristics were he submitted for a PET scan :)