The Gene Illusion

The Gene Illusion is a book by clinical psychologist Jay Joseph challenging 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.

History of twin research
In Chapter 2 Joseph concentrates on the history of twin research, making much its origins in eugenics, racism, and the German racial hygiene movement. For the most part, twin researchers have failed to provide details of these origins. 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), who share 100% genetic similarity, versus the resemblance of reared-together same-sex fraternal (dizygotic), 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, known as 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 twins. However, Joseph argues that the equal environment assumption is untenable on several grounds. He therefore 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 twins.

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 ( Thomas J. Bouchard, Jr.’s Minnesota 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 such as Bouchard’s, according to Joseph, is that the investigators mistakenly compared reared-apart identical twins (“monozygotic twins reared-apart,” or “MZAs”) to ‘‘reared-together’’ identicals—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. (Bouchard’s group attempted to correct MZA correlations for age and sex effects, but Joseph argues that these adjustments were inadequate and unclear.) 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 would find that the biologically-unrelated pairs correlate similarly to MZAs, which would suggest that MZA correlations are 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.

Heritability
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 virtual 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 before they were discredited by their association with eugenics, Nazism, and German “criminal biology.” 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.

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 points out that genes for the major psychiatric disorders remain undiscovered, and that the reason may be that 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.

Conclusion
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.

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.