As expected, we have seen several new gene discovery claims in psychiatry during the past 12 months, which like previous such claims put forward since the 1960s, are unlikely to be replicated. I might examine one or more of the studies these claims are based upon in future posts.
It has been over a year since my last post, as I have been working on a new book whose hardcover edition is scheduled to be published next month by Routledge. The title is The Trouble with Twin Studies: A Reassessment of Twin Research in the Social and Behavioral Sciences. For more information, please see the Amazon.com page and the Taylor & Francis page. The book approaches twin research in the social and behavioral sciences from a critical perspective, with a special emphasis on so-called studies of “reared-apart” twins. The most famous investigation of this type is the Minnesota Study of Twins Reared Apart, whose major problem areas are covered in depth in Chapters 5 and 6, and may be the subject of a future MIA post. Although I have examined various aspects of twin research in two previous books, in the new book I look at the major issues much more closely, with a fresh perspective based on the very latest research findings.
While reared-apart twin studies have focused on psychological characteristics such as IQ and personality, the mainstay of psychiatric genetic research, and the basis of genetic theories and claims in psychiatry, have been “twin method” studies which compare the behavioral resemblance of reared-together identical versus reared-together same-sex fraternal twin pairs (see my March 13th, 2013 MIA post). I devote two chapters to the fallacy of the twin method and its clearly false underlying assumption that identical and fraternal twins grow up experiencing similar behavior-shaping environments (the “equal environment assumption”).
Although supporters of psychiatric genetic twin studies argue that the equal environment assumption has been tested and upheld, almost everyone (twin researchers and their critics alike) agrees that reared-together identical pairs grow up experiencing much more similar environments than experienced by same-sex reared-together fraternal pairs. Almost everyone also agrees that identical pairs resemble each other more than fraternal pairs for most psychiatric disorders. Therefore, although completely overlooked by psychiatry and psychiatric genetics, the best-replicated disconfirmation of the validity of the twin method’s equal environment assumption consists merely of all the psychiatric twin studies ever performed. Nine decades of such studies have shown, with almost complete uniformity, that pairs experiencing similar environments and high levels of identity confusion and attachment — identicals — resemble each other more for psychiatric disorders than do pairs experiencing less similar environments and much lower levels of identity confusion and attachment — fraternals.
In addition to twin research, in the Trouble with Twin Studies chapter on twin research in psychiatry I examine mainstream psychiatry’s position that psychiatric disorders are valid medical conditions that can be reliably diagnosed. I argue that the current (scientifically unsupported) emphasis on brain disorders and genetics in psychiatry causes the field to overlook or de-emphasize many environmental factors that have been shown to play an important role in causing emotional distress and dysfunction.
Ironically, if molecular genetic research had actually delivered the genes for psychiatric disorders promised by mainstream psychiatry and its subfield of psychiatric genetics, twin research today would be largely obsolete because focus would have shifted to molecular genetic research, and a person’s genotype and diagnosis would be determined directly from his or her DNA. Twin research, therefore, retains its current level of importance in psychiatry only because the genes believed to exist for its disorders, based largely on genetic interpretations of twin studies, have not been found.
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