We are approaching a period of crisis and
reevaluation in the behavioral genetics and psychiatric genetics fields, as
attempts to discover “genes for behavior” have, with possible rare exceptions,
been unsuccessful. Schizophrenia is the most investigated psychiatric disorder,
yet although there have been many claims of gene “association,” decades of
molecular genetic studies have failed to produce a single causative gene. In an
official 2013 press release, the American Psychiatric Association admitted that
psychiatry and its psychiatric genetics subfield are “still waiting” for the
identification of “biological and genetic markers” for psychiatric disorders.
Although some gene discovery claims have appeared since then, psychiatry
continues to “wait.”
In this context, Jay Joseph focuses on the
methodological shortcomings and questionable assumptions of previous
schizophrenia family, twin, and adoption studies. He shows that although
genetic interpretations of schizophrenia twin studies are based on the
assumption that reared-together monozygotic (MZ) and dizygotic (DZ) twin pairs
grow up experiencing similar (“equal”) behavior-influencing environments, this
assumption is clearly false. He concludes that schizophrenia twin studies, like
schizophrenia family studies, are unable to disentangle the potential impact of
genetic and environmental influences. In both types of studies, therefore, the
results can be explained entirely by non-genetic factors.
Turning to adoption research, Joseph puts the
influential Danish-American adoption studies of the 1960s-1990s under the
microscope, taking readers on a journey through massively flawed, biased, and
environmentally confounded studies that have been presented in standard
textbooks in a misleading manner since the 1970s. These texts have ignored or
concealed methodological, factual, and even scientific-ethical flaws that, in
addition to twin studies based on the false assumption that MZ and DZ
environments are equal, call into question everything that we supposedly “know”
about the genetics of schizophrenia. The authors of these texts often fail
to mention studies that do not fit genetic explanations, while on occasion they
cite studies that do not exist.
In contrast to the prevailing beliefs in the
social and behavioral sciences, Joseph argues that there is little if any
scientifically acceptable evidence that disordered genes play a role in causing
schizophrenia. At the same time, he highlights the evidence in favor of
environmental causes, while noting that the validity of the “schizophrenia”
concept itself has a long history of controversy.
In this book, which brings together many of
Joseph’s previous findings in one place while exploring many new areas, the
main issues are approached from a refreshingly critical perspective. This
stands in direct contrast to the cookie-cutter academic and journalistic
accounts of the “genetics of schizophrenia” topic, where it is usually claimed
that schizophrenia is a “highly heritable” disorder involving a disease process
of the brain.
Joseph presents an up-to-date, thoroughly
documented, and much needed critical evaluation of schizophrenia genetic
research. His findings have important implications for psychiatry, behavioral
genetics, and for the social and behavioral sciences in general. In addition,
this work is essential reading for anyone interested in the longstanding
“nature-nurture” question of whether human behavioral differences are caused
mainly by hereditary or by environmental factors. Joseph concludes that the
failure to discover genes for schizophrenia, psychosis, and other psychiatric
conditions is not a scientific setback but is instead a cause for celebration,
as society can now part ways with genetic diversions and medical approaches,
and can focus on environmental causes, social interventions, non-medical
treatment approaches, and prevention.