Thursday, August 25, 2011

The Fallacy of Extreme Genetic Determinism

While attending a recent conference on the west coast, I had some time to read the New York Times and my interest was peaked by the headline on the story below:

Here is a synopsis of the news report.  Gary Cossey had pleaded guilty to to a single count of possessing child pornography.  At the sentencing hearing expert psychologists for the defendant testified that Mr. Cossey was not a high risk repeat offender in-part because he had voluntarily been participating in therapy sessions with signs of responding positively to therapeutic interventions.

Nevertheless, the judge rejected these arguments because it was very likely that Cossey would commit repeated offenses stating: "It is a gene you were born with.  And it is not a gene you can  get rid of,"  Judge Gary Sharpe then sentenced Cossey to a prison term of 6.5-years, a life term of supervised release, and a $100 court fee.

However, a court of appeals overturned the sentence* because there was no evidence to support the assertion that Cossey would inevitably repeat his offenses due to a child pornography gene. Neither is there undisputed evidence that such a gene exist. The appeals court then ordered that another judge be appointed to preside over a re-sentencing hearing to determine a Cossey's final jail sentence.

But what if there were such a gene?  What if it were not a trait that was expressed according to classic laws of Mendelian inheritance, but was a polygenetic trait?  Would it be the case in either instance  that a person with this gene or genes would inevitably be either a consumer or purveyor of child pornography? 

To what extent do our genes determine our thoughts and our actions?  If genes do determine thoughts and actions, are we at all responsible for them? Is free will a fiction?  Interestingly, if genes had ultimate control over our behaviors, rather than using this to justify someones incarceration, it could also be reasonably argued that such persons should not be jailed or otherwise held accountable for their actions. Either argument is deeply troubling.

Arguments based upon this dichotomy - between genes or environment, or genetic determinism and free will - are overly simplistic.  Of course both genetic factors as well as environment influence our how our bodies function, as well as our thoughts and behaviors.  For example, many psychological disorders (e.g., schizophrenia)  have been found to be attributable to genetic factors; but genetic factors do not account for all the influences that determine overall risk.   

Twin studies have shown that risk of schizophrenia is influenced by genetics since the concordance of schizophrenia among pairs of monozygotic twins is roughly twice that seen among dizygotic twins.  Yet the concordance among identical twins is just 50%,  In only 50% of those pairs of monozygotic twins in which one twin is diagnosed as schizophrenic, is the other twin also schizophrenic.  Some variability in risk may be attributed to interaction among numerous genes, but even polygenetic means of inheritance can not adequately explain the less than 100% concordance for schizophrenia that is observed among monozygotic twins.  Obviously, there must be some additional factor(s) influencing each twin's actual risk of becoming schizophrenic. 

What may this factor or these factors be?  How do other factors influence the degree of genetic risk that each twin has of becoming schizophrenic?   Enter the epigenome.

The epigenome is comprised of those portions of the DNA that are not genes; the DNA that literally surround genes.  If genes are characterized as the hardwired components of our genome, then the epigenome can be thought of as the software that determines, which genes are expressed, when they are expressed and in what cells they are expressed. What this means is that any one of us may have a gene or a set of genes that all might contribute in some degree to our risk of psychological or behavioral impairments or attributes; but the epigenome determines if, when where and how those genes are expressed or suppressed. 

This is why, even among identical twins, one twin may be diagnosed as schizophrenic but their sibling is comparatively healthy.  In one instance patterns of gene expression orchestrated by the epigenome of the affected twin likely differed than those patterns of gene expression orchestrated by the epigenome of the healthy twin. 

In a way, the epigenome is evolutions means of hedging the genetic investment that are made at the time of our conception - at the point when our unique personal genomes are created.  Our genetic destiny is not determined solely by those genes we inherit at conception, but can be further modified by the epigenome through our subsequent interactions with the environment.  This is why belief in extreme genetic determinism is a fallacy.

If you want to explore a very accessible resource regarding epigenomics, follow this link:

* Note that they overturned the sentence, not Cossey's guilty plea.  To date, I've been unable to learn what sentence Cossey was given during re-sentencing hearings.

To gain a legal perspective on this case visit this blog: and this website: American

Cited Sources
  • Caspi, A., McClay, J., Moffitt, T.E., Mill, J., Martin, J., Craig, I.W., Taylor, A., & Poulton, R. (2002). Role of genotypes in the cycle of violence in maltreated children. Science, 297, 851-854. DOI: 10.1126/science.1072290.
  • Caspi, A., Sugden, K., Moffitt, E.E., Taylro, A., Craig, I.W., Harrington, H., McClay, J., Mill, J., Martin, J., Braithwaite, A., & Poulton., R. (2003). Influence of life stress on depression: Moderation by a polymorphism in the 5-HTT gene. Science, 301, 386-389. DOI: 10.1126/science.1083968. 
  • Weiser, B. (2011). Court rejects judge's assertion of a child pornography gene. The New York Times, 160 (55,300), A20.

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