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Schizophrenia Genetic Research: Still Running on Empty

By Jay Joseph, Psy.D.


Awais Aftab’s arguments in his 3/21/2020 post “Defending Aggregate Genetic Effects in Psychiatric Disorders” are based largely on his claim that the “high genetic heritability of schizophrenia” and other major psychiatric disorders “has been pretty consistently reported in [the] literature.” Indeed it has, but the “literature” could still be wrong, especially when it is based on the acceptance of false assumptions, and on textbook and other authoritative authors’ frequent failure to critically analyze (or even read closely) the original “landmark” studies they cite. Not to mention that, as a pairof criticswrote, “The term ‘heritability,’ as it is used today in human behavioral genetics, is one of the most misleading in the history of science.” (See my description of the “heritability fallacy” HERE.)
Aftab then asked, in relation to Duncan Double’s 3/20/2020 commentary “The Causes of Psychiatric Illness,” whether Double can “cite even one good study which demonstrat…

It’s Time to Radically Reevaluate “Reared-Apart” (Separated) Twin Studies

Summary and Link to the Main Article
It’s Time to Radically Reevaluate “Reared-Apart” (Separated) Twin StudiesBy Jay Joseph, Psy.D.August 9th, 2020
(Link to the full article pdf HERE)The “validity of twin studies” question is very important because these studies supply the main “scientific” evidence in support of the “nature” (genetic) side of the long-running “nature-nurture” debate. The question of whether genes or environments are the main cause of human behavioral differences has profound implications for social relations and political policy decisions.In a previous article I summarized the critique of “twin method” studies, which use reared-together twins. I argued that the main assumption these studies are based on is false, and I concluded that the twin method should be abandoned as a tool for the detection of genetic influences on behavior. In the present article I summarize and add to the main arguments that I and other critics have made against genetic interpretations of the r…

It’s Time to Abandon the “Classical Twin Method” in Behavioral Research

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(Note: This article is an updated and greatly revised version of a 2018 articlethat appeared at the “Mad in America” website. Many more articles on twin research and behavioral genetics can be found at https://www.madinamerica.com/author/jjoseph/. My 2020 analysis of twins reared apart studies can be found HERE)
(Last revision: 8/17/2020)


By Jay Joseph, Psy.D.


Twin studies supply the “scientific evidence” most often cited in support of the claim that human behavioral differences are strongly influenced by heredity. Yet genetic interpretations of twin studies of behavior, including areas such as IQ, personality, criminality (antisocial behavioral), schizophrenia, and depression are based on the acceptance of highly questionable or even false assumptions.I am compelled to keep writing about this because these studies have not gone away, despite the critics’ airtight arguments that indicate that they should have gone away a long time ago.
Some people argue that recent molecular genetic rese…