When having a good debate on a given topic, there will usually be arguments ranging from one extreme to the other (and anywhere in between). The true answer you will find, is never those extremes.
The middle ground is sometimes hard to maintain in discussions and debates because the extremes keep hitting each other in the head, making impenetrable noise as they do so. Examples I have been involved in lately are debates on race, IVF, abortion, junk-DNA and open access publishing. Arguably, this mechanism is present for almost any discussion. So also for the the debate on how much of human nature is shaped by genes and how much by the surrounding environment, -the nature vs. nurture discussion.
Reassuringly though, as most debates mature, they do tend to move towards the golden mean. Most people are confident now that human biology (behavior) is a result of a combination of our genes and the environment in which we live and grow. I am confident about this too, but I see research giving support to this notion far to seldom. First example I remember, was this article on domestic violence and genetics:
A functional polymorphism in the gene encoding the neurotransmitter-metabolizing enzyme monoamine oxidase A (MAOA) was found to moderate the effect of maltreatment. Maltreated children with a genotype conferring high levels of MAOA expression were less likely to develop antisocial problems. These findings may partly explain why not all victims of maltreatment grow up to victimize others, and they provide epidemiological evidence that genotypes can moderate children’s sensitivity to environmental insults. – Caspi A et al. Role of genotype in the cycle of violence in maltreated children.Science. 2002 Aug 2;297(5582):851-4.
I remember reading it and thinking, – yes !! Finally some evidence proving what we all thought we already knew . And I’ve kept waiting for other reports to similarly illustrate this gene/environment interplay so clearly (for the record, I know that the MAOA-results have not been unequivocally reproduced). Now, I have seen sporadic reports on other gene/environment interactions, but the mountain of evidence I had been expecting since 2002 just has not appeared.
That’s why when I read this review on ADHD the other day, which was exemplary in referencing and discussing gene/environment interactions, I was pleased and reassured that this field is far from forgotten about. Here are some descriptive quotes:
The neurobiology of psychiatric disorders is not about inevitability but is instead about vulnerability and propensity; it is only in certain environments that the disease is likely to emerge.
One of the explanations why results of genetic studies of ADHD have been contradictory is that not all individuals carrying a vulnerable genotype develop the disorder as the genetic effect may only become apparent among the subgroup of individuals exposed to a certain environmental risk. Thus, the importance of studying gene–environment interactions in behavioral disorders lies in the hypothesis that some genes show effects only in groups of individuals subjected to specific environmental stressors. – Kieling C at al. Neurobiology of attention deficit hyperactivity disorder.Child Adolesc Psychiatr Clin N Am. 2008 Apr;17(2):285-307, viii.
There is the definite possibility that I may not have paid enough attention and contrary to what I believe, one can find a mountain of publications on gene/environment interactions. If not (and I’m right), the reason there aren’t that many publications on this topic may be that research into this field is really hard to do. And that of course, is a good excuse.
But, regardless of the presence of this mountain or not: in order to use genetic research with any confidence in medical practice (and future research), the exact contributions from genes and environment needs to be worked out for as many traits as possible. And that (I hope) is our inevitable future – knowing our genes and what they will do to/for you given your surroundings. Subsequently, being able to manipulate these two factors will transform both nature and nurture. Potentially, we’ll reach the golden mean.