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The Gene Illusion

The Gene Illusion [1] is a book by clinical psychologist Jay Joseph[2], published in 2003, which challenges the evidence underlying genetic theories in psychiatry and psychology. Focusing primarily on twin and adoption studies, he attempts to systematically debunk the methodologies used to establish genetic contributions to schizophrenia, criminal behaviour, and IQ. Joseph's criticisms of genetic research in psychiatry have found their place within the "anti-psychiatry" movement.

Additional recommended knowledge


History of twin research

In Chapter 2 Joseph concentrates on the history of twin research, making much of its origins in eugenics, racism, and the German racial hygiene movement. Beginning with Francis Galton, Joseph discusses the various ways that twins have been used for research purposes, as well as some of the methodological problems discussed by critics. Due to its association with Nazism and eugenics, interest in twin research waned in the late 1940s and 1950s, but began a revival in the late 1960s that continues to the present time. Today, twin studies constitute a major pillar of support for genetic theories in psychiatry and psychology.

The "classical twin method"

Joseph looks closely at the theoretical underpinnings of twin research in Chapters 3 and 4. A major tool of behavioral genetics and psychiatric genetics is the “classical twin method,” more commonly known as “the twin method.” The twin method compares the resemblance of reared-together identical (monozygotic) twin pairs, who share 100% genetic similarity, versus the resemblance of reared-together same-sex fraternal (dizygotic) pairs, who average a 50% genetic similarity. Twin resemblance is usually measured with concordance rates or correlations. Based on the assumption that both types of twins experience equal childhood and adult environments (the “equal environment assumption” or “EEA”), twin researchers attribute to genetic factors the usual finding of a significantly greater resemblance among identical versus same-sex fraternal twin pairs.

However, Joseph shows what he believes to be overwhelming evidence that identical twin pairs experience much more similar environments than fraternal pairs, and, perhaps more important, identical pairs experience a stronger psychological bond and more often experience identity confusion.

Twin researchers usually concede that identical twin pairs experience more similar environments, but argue that this is not the case for “trait relevant” aspects of the environment that have been shown to contribute to the trait in question. They also claim that identical twins “create” more similar environments for themselves by virtue of their greater genetically-caused similarity of behavior.

Joseph concludes that there is no reason to accept that the twin method measures anything other than the more similar treatment, greater environmental similarity, and closer psychological association experienced by identical versus fraternal twin pairs.

Twins reared apart

Joseph turns his attention to twins reared apart (TRA) studies in Chapter 4. Problems in this area include (1) the questionable “separation” of twins, who in many cases grew up together in early childhood and had quite a bit of contact over much of their lives; (2) the similarity bias of the samples; (3) researchers’ failure to publish or share raw data and life history information for the twins under study, and (4) the impact that the researchers’ bias in favor of genetic explanations may have had on the interpretation of their results.

However, the main problem with TRA studies according to Joseph, is that the investigators mistakenly compared reared-apart identical twin pairs (“monozygotic twins reared-apart,” or “MZAs”) to ‘‘reared-together’’ identical pairs—thereby failing to control for the fact that both sets share several important environmental similarities. These include common age (birth cohort), common sex, similar appearance, and similar political, socioeconomic, and cultural environments. Thus, Joseph argues that all previous TRA researchers used the wrong control group, leading to their erroneous conclusions in favor of genetics.

Joseph writes that a scientifically acceptable study would compare the resemblance of a group consisting of MZAs reared apart from birth and unknown to each other, versus a control group consisting not of reared-together identical twins, but of biologically unrelated pairs of strangers sharing all of the following characteristics: they should be the same age, they should be the same sex, they should be the same ethnicity, the correlation of their rearing environment socioeconomic status should be similar to that of the MZA group, they should be similar in appearance and attractiveness, and the degree of similarity of their cultural backgrounds should be equal to that of the MZA pairs. Moreover, they should have no contact with each other until after they are evaluated and tested. After concluding such a study, Joseph believes that we might find that the biologically-unrelated pairs correlate similarly to MZAs on psychological tests, which would suggest that MZA correlations are mainly, if not entirely, the result of environmental influences. Because no study of this type has ever been attempted, and because of the major flaws and biases in the studies that have been undertaken, Joseph argues that we can draw no valid conclusions in support of genetic influences on psychological trait variation from reared-apart twin studies published to date.


Joseph argues in Chapter 5 against the utility of the concept of heritability in psychology and psychiatry, claiming that the heritability statistic is misleading as a measure of the genetic contribution to a trait. For Joseph, heritability is suitable only for plant and animal breeders, for whom it was originally developed.

Genetics of schizophrenia

Chapter 6 begins a two-part critical examination of the evidence that genetic factors play a role in causing schizophrenia, the classical psychiatric disorder. Although the genetic basis of schizophrenia is currently seen as a virtually proven fact in psychiatry and psychology, Joseph argues that the evidence supporting this position is weak. On the basis of his position laid out in previous chapters, Joseph argues that schizophrenia twin research provides no support to genetic theories of schizophrenia. These theories typically hold that schizophrenia is caused by a genetic predisposition in combination with exposure to environmental triggers.

The schizophrenia adoption studies of the 1960s and 1970s are largely responsible for closing the “genetics of schizophrenia” debate. In Chapter 7, Joseph undertakes an in-depth analysis of these studies, which were carried out in the United States, Denmark, and Finland. He argues that schizophrenia adoption research contains numerous methodological flaws and biases, which include (1) inconsistent and biased methods of counting relative diagnoses; (2) the frequent failure to adequately describe the basis upon which a schizophrenia diagnosis was arrived at; (3) counting first- and second-degree relatives with the same weighting; (4) the lack of case history information, which would allow reviewers to assess the environmental conditions experienced by adoptees and relatives; (5) the bias introduced by counting relatives individually, which violates an assumption of the statistical measures used; (6) the use of late-separated or late-placed adoptees; (7) evidence that the investigators’ bias in favor of genetic explanations had an important influence on their methods and conclusions; and (8) selective placement bias.

Regarding selective placement, all schizophrenia adoption studies were performed in countries that enforced eugenic sterilization laws in the era in which adoptees were placed. Because schizophrenia and insanity were believed to be caused by “hereditary tainting,” it is likely that genetically stigmatized children were placed into homes inferior to those experienced by non-stigmatized children. Thus, Joseph argues that the basic assumption of adoption studies—that experimental and control adoptees experienced comparable rearing environments—was violated. On the basis of what he argues is a body of faulty research, Joseph calls for re-opening the debate on the role of genetics in schizophrenia and other psychiatric disorders.

Genetics of criminality

In Chapter 8, Joseph examines twin and adoption studies of criminal and antisocial behavior. Genetic theories of criminality have been regaining the foothold they had (in particular in the Italian school of criminology) before they were discredited by their association with eugenics, Nazism, and German “criminal biology” during the Nazi regime. Joseph argues that, like schizophrenia, the reported greater resemblance of identical versus fraternal twins for criminality found in some of the studies can be plausibly explained on environmental grounds. Joseph then moves on to criminality adoption studies, where he highlights important flaws and biases.

Joseph concludes that family, twin and adoption studies provide no scientifically acceptable evidence for the existence of a genetic predisposition for any type of “criminal,” “psychopathic,” or “antisocial” behavior, however it has been defined at any given time or in any given society. Finally, given (1) the potential social impact of criminal genetic research, which includes the further unwarranted stigmatization of ethnic minorities; (2) the well-known social factors leading to crime; and (3) the political aspects of deciding who is and is not labeled a criminal, it is questionable whether this type of research should even be performed.

Intelligence (IQ) and genetics

Joseph examines the argument that intelligence (as allegedly measured by standardized IQ tests) has an important genetic component. While looking briefly at research cited in support of this argument, Joseph chooses to emphasize what he sees as flaws and biases in the intelligence tests themselves. Specifically, he argues that assumptions about the lower intelligence of the working class and oppressed ethnic groups are ‘‘built into’’ IQ tests. Thus, he wonders how anyone who knows how these tests are constructed could argue that the lower IQ scores of African-Americans versus whites, or working class versus upper class, are the result of genetic differences.

Molecular genetics

In Chapter 10, entitled ‘‘Molecular Genetic Research in Psychiatry and Psychology: An Exercise in Futility?,’’ Joseph argues that genes for the major psychiatric disorders are unlikely to be discovered because such genes do not exist. Similarly, he argues that molecular genetic studies of IQ and personality in behavior genetics are also doomed to failure. The belief that such genes exist is based on the results of family, twin, and adoption studies, which molecular genetic researchers interpret as evidence in favor of genetics. Joseph argues throughout his book, however, that this body of research does not provide scientifically acceptable evidence in favor of genetics.


In his final chapter, Joseph sums up his critique of family, twin, and adoption studies. He calls on the psychiatry and psychology fields to perform a critical reassessment of whether these research methods provide solid evidence in support of genetics. In addition, he calls for a reassessment of behavior geneticists’ use of concepts such as “heritability,” “IQ,” and “personality.” Furthermore, Joseph warns that the current ascendancy of genetic theories and genetic determinism, albeit on the basis of faulty research, could lead to a rebirth of the eugenics movement.


In a 2004 review of The Gene Illusion, German behavior geneticist Frank Spinath objected to Joseph’s —

unwarranted (and unqualified) conclusion that the methodological difficulties and challenges in behavior genetic research render the approach meaningless and invalid.

Furthermore, according to Spinath, "little is said about the field’s [behavior genetics] advances."[3] Spinath also objected to Joseph’s tendency to "polarize" the discussion about genetics. In a 2005 exchange with Joseph in the American Journal of Psychiatry, noted psychiatric genetic researcher Kenneth Kendler wrote:

It is one thing to criticize the methodology of specific studies. It is quite another to suggest, as Dr. Joseph does, that we reject the results of an entire field of scientific inquiry. This might have been warranted for some pseudoscientific systems, such as astrology, alchemy, and the Ptolemaic astronomic system. It is highly unlikely that modern psychiatric genetics will be judged by future historians of science to be in such company.[4]

Another critique of Joseph's book was provided by Hanson[5]. Hanson faults Joseph for applying current day standards to old research, while ignoring modern efforts:

This book is an exhaustive look backward in time at the research providing the foundations for modern efforts to understand the biology of mental illness and intelligence. This is not a balanced and current appraisal of the state of behavior genetic findings and theories. (...) What domain of science would stand up to the application of current day standards applied to efforts from decades past?

In addition, Hanson, who is a practicing psychiatrist[1], faults Joseph for ignoring suffering and not providing any alternatives to the research that he attacks so vehemently:

After a maelstrom of attacks on his opponents, the boxer devotes only two pages to “a new approach.” Unfortunately, the author mostly recapitulates his previous criticisms and provides neither new insights nor new research strategies. It is so much easier to cast stones than to create gems. I read this book while sitting in my small office buried deep in an institution so large that the roof measures seven acres. My courageous little green philodendron provides counterpoint to endless beige. Into this space, about 45 times a week, people enter, with one form or another of severe emotional distress, seeking my help. Their distress developed long before I, or any other mental health professional, applied a psychiatric label to their condition. Their distress is profound, leading some to the threshold of suicide. These people bring me questions that I cannot answer: “Why did this happen ... when will it end ... one of my parents had the same problem, what about my children ... ?” Does The Gene Illusion: Genetic Research in Psychiatry and Psychology Under the Microscope help me answer these questions? No. On workdays when I'm not in the clinic, I sit in my little office reading, analyzing data, and writing with the informed belief that someday research will provide answers to the questions brought to me by the people I serve. Does The Gene Illusion give me direction for better science in the future? No, it does not.

Joseph published his second book, The Missing Gene: Psychiatry, Heredity, and the Fruitless Search for Genes in 2006. In addition to other topics, he examines the claim that autism, attention-deficit hyperactivity disorder (ADHD), and bipolar disorder have a genetic basis. Like schizophrenia, he concludes that the evidence in support of genetics in these areas is weak.

See also


  1. ^ The Gene Illusion: Genetic research in psychiatry and psychology under the microscope, Joseph, J (2003). PCCS Books. ISBN 1-898059-47-0
  2. ^ An interview with Jay Joseph
  3. ^ Spinath, F. M. (2004). [Review of the book The Gene Illusion: Genetic Research in Psychiatry and Psychology Under the Microscope]. Intelligence, 32, 425-427
  4. ^ Kendler, K. S. (2005). Dr. Kendler responds [Letter to the editor]. American Journal of Psychiatry, 162, 1985-1986
  5. ^ Hanson, D. (2005) The Gene Illusion Confusion. PsycCRITIQUES, 50, no 52, art 10
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "The_Gene_Illusion". A list of authors is available in Wikipedia.
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