Not in Your Genes: The Real Reasons Children Are Like Their Parents
A well known (in the UK, anyway) clinical psychologist, Oliver James, has written a book called Not in Your Genes: The Real Reasons Children Are Like Their Parents which reports that in the Human Genome Project there are yet to be discovered any genes responsible for psychological disorders. While geneticists might claim that they simply haven't discovered them yet, James goes onto conclude that in the meantime it is reasonable to claim that psychological disorders are not genetic. This he bases on his lifetime professional experience and illustrates with examples from his own family and other families he has worked with where parent child relationships have led to the child having psychological disorders as an adult. James states that the first three years of life are the most important for imprinting of psychological information and that parents are at the forefront of this influence.
I would disagree with James that it is all about the parents. If the first three years of life are the most important, then any illnesses suffered during that period may well have a psychological effect. A serious bout of Whooping cough, Hepatitus or Chicken Pox before age 3 could have a diminishing effect on psychological development, by reverting resources otherwise needed for balanced development, into simply staying alive. James does reference this slightly when he says "I am also not ruling out physical causes for psychological traits. There's a whole business about the long-term effects of what happens in pregnancy that will, perhaps, one day turn out to be hugely important. However, with psychosis - whether it be bipolar or schizophrenia - there is just a mass of evidence that something has gone horribly wrong in the family", however this is only pregnancy that he references and not the post natal years.
Physical effects of pregnancy, and by this we include environmental aspects of pregancy, the mother's diet, her psychological and physical fitness and how that transmits into the womb, may well be the confound in twin studies that have suggested genetic links with psychological disorders. Twin studies typically investigate twins who have been separated at birth and put into entirely different environments for their upbringing. Propensity for psychological disorders are measured between the twins and more often than not found to be related more than is possible by chance, leading to conclusions that psychological disorders are genetic. However, the experiments usually fail to acknowledge that both twins have shared the same womb already for 9 months and it is possible that physical effects of the same pregnancy result in an increased propensity for a psychological disorder in both twins. The only way to truly test genetic links by this method is to separate the twins not long after conception, which is impossible.
We have yet to understand what physical effects of pregnancy might have on psychological development. We know for sure that Fetal Alcohol Syndrome is a reality and that is entirely a physical effect that is due to the behaviour of the mother during pregnancy. We are yet to understand what other maternal behaviours have lasting behavioural effects, however small or subtle which might add up to developmental disaster. On top of that we need to understand more about the lasting effects of biological insults (diseases and such) that occur during infancy. Certainly the road to understanding psychological disorders is not an easy one and parents shouldn't be given the bulk of the "blame"