Sunday, July 20, 2008

Genes, Environment and Violence

I have posted a couple of posts before on genetics and violence (see here and here), and this paper (by Guo, Cai and Roettger) in the latest issue of the American Sociological Review is an excellent example of how the genetic revolution will have a profound impact on our understanding of human behaviour. The UNC press release is here.

Here is a sample from this fascinating study:

Why do some individuals become serious and violent delinquents while others do not, despite growing up in similar social contexts and participating in similar social processes? We maintain that part of the answer lies in genetic propensities. Social conditions may be sufficient to produce delinquency in some individuals, whereas for others both social conditions and genetic propensities may be needed to make a difference. The relationship between social conditions and genetic propensities may be additive or interactive. To illustrate, suppose that family disruption and genetic propensities each increase the probability of a delinquent act by .1. If the two are additive, the total increase would be .2 when both are present. If the two are interactive, the total could be .4, significantly larger than .2. In such a scenario, genetic propensities could amplify the effect of family disruption or family disruption could amplify the effect of genetic propensities.

....The key innovation of this study is the incorporation of molecular genetic variants into a social-control life-course model of delinquency. We use three genetic polymorphisms in the DAT1, DRD2, and MAOA genes to measure genetic propensities for delinquency and criminality. All three genetic variants are significantly related to self-reported serious and violent delinquency in a model of social control—a social-control model that includes social-structural conditions and a number of indicators for family and school processes.

....Our findings confirm that genetic effects are not deterministic. The expression of the genes may depend heavily on environment. In both the MAOA and DRD2 models, the genotype effect changes dramatically when an interaction with environment is allowed. Conversely, the socialcontrol effect also changes radically once an interaction with a genetic variant is introduced. The latter point can be illustrated by the MAOA*2R grade retention interaction result for serious delinquency in Table 7. For those who do not have a 2R allele, repeating a grade raises serious delinquency by .451, but for those possessing a 2R allele, repeating a grade raises serious delinquency by a drastic 6.61.

....Emerging molecular genetic evidence suggests that individuals may differ in innate propensities for a wide variety of traits and behaviors. As genetic evidence increasingly points to intrinsic individual differences, the social sciences may need to incorporate this development. In studies investigating causes of delinquency, the incorporation of genetic evidence may help to estimate social-control effects (which may be correlated with genetic effects) more precisely, improve model prediction, and reveal interactions with social-control processes. The development of contemporary molecular genetics has created challenges and opportunities for the social sciences. Meeting the challenges and opportunities will advance our understanding of how individual traits and behaviors are affected by social processes.