Nature and Nurture Revisited: A Chronicle of the Landmark Minnesota Twin Study

On August 15, 1992, Arthur Jensen delivered a well-received speech to a packed audience at the Centennial Convention of the American Psychological Association in Washington, D.C. Jensen’s invited address, “The Cyril Burt Scandal, Research Taboos, and the Media,” focused on the investigative findings of two meticulously researched books (Robert Joynson’s The Burt Affair and Ronald Fletcher’s Science, Ideology, and the Media: The Cyril Burt Scandal) which all but exonerated Cyril Burt, the eminent British psychologist, of allegations of fraud in his study of identical twins reared apart.

Burt’s detractors seized on suspicious statistical anomalies to claim that he fabricated data in his twin study findings. Insufficient details of the collection and analysis of data on Burt’s part helped fuel the speculation that Burt fudged some of his work. Joynson and Fletcher independently concluded that the totality of the evidence of fraud was based on conjecture, innuendo, and exaggerations. Both authors presented a compelling case that Burt’s critics intentionally set out to discredit one of the most distinguished reputations in the annals of British psychology. Fletcher and Joynson marshaled enough counter evidence to show that Burt’s detractors rushed to judgment, made claims that were eventually found to be untrue (such as missing assistants), and omitted crucial evidence, some of which was intentionally destroyed, that may have exonerated Burt of misconduct.

The International Ballroom West of the Washington Hilton Hotel was packed with several hundred APA attendees, including a number of noteworthy psychologists. Jensen showed photos of Burt from his own collection, relayed what it was like to work as Burt’s understudy, and summarized the case for Burt’s defense. He explained some of the animosity of Burt’s detractors and the likely personal and political motivations for discrediting such a distinguished psychologist.

Jensen’s remarks were based, in part, on a book chapter, “Scientific Fraud or False Accusations? The Case of Cyril Burt,” that was published in 1992. Here’s how Jensen summarized the Burt fiasco:

The case of Sir Cyril Burt is probably the most bizarre episode in the entire history of academic psychology. This is due to a unique combination of elements — the socially touchy subject of Burt’s major research; his genuinely outstanding accomplishments; his mysteriously complex character; and finally, some years after his death, the damaging accusations leveled against him and the extreme and strangely virulent vilifications of his reputation that ensued. Burt’s posthumous worldwide notoriety surely exceeds the considerable fame and acclaim he enjoyed during his long and immensely distinguished career.

One psychologist who attended Jensen’s lecture was Nancy Segal.  As the assistant director of the Minnesota Center for Twin and Adoption Research in the psychology department at the University of Minnesota, Segal helped manage one of the most important twin study projects in the last half of the twentieth century. She has written the definitive account of the Minnesota Study of Twins Reared Apart (MISTRA) in Born Together-Reared Apart published last June by Harvard University Press.

In the introduction Segal captures what she refers to as “the Climate of the Times.” The Burt case, as Segal notes, has larger implications for twin study research. On the one hand Burt’s data is no longer relevant given the reliability of data from other twin studies. On the other hand, Burt’s detractors understood the significance of twin studies research: it offers a unique window on human nature. Specifically this research tool is used to sort out the influence of heredity and environment on human development, in particular, differences in personality, intelligence, psychopathology, social attitudes, and other traits and attributes.

The significance of Burt’s research findings compared with that of the MISTRA results is that both produced identical genetic correlations on intelligence: 0.771 for identical twins reared apart. As Jensen noted in his 1992 lecture, if Burt in fact faked his data, he had the clairvoyance to make up an accurate statistical correlation to the third decimal point! (As a birthday gift some years later, Segal and another assistant presented Bouchard with a t-shirt that featured the number “.771” stamped on the shirt.)

Learned scholars such as Segal, Thomas Bouchard, the director of MISTRA, the late David Lykken, a pioneering psychologist and MISTRA researcher, David Rowe, Lee Willerman, and many others have punctured the behaviorist stranglehold that dominated the profession for decades.

Marxist ideologues committed to extreme egalitarian environmentalism—such as Leon Kamin, Ashley Montagu, and the late Stephen Jay Gould—have been the harshest critics of behavior genetic research. Kamin and Gould seized on Burt’s statistical anomalies in their failed attempt to discredit an entire field of research. These critics understand the broad ramifications that twin study findings can yield — illuminating the comparative contributions of genes and environment as well as their interactions in shaping behavioral differences. If genes play a substantial role in mental abilities, the effectiveness of social engineering programs advocated by egalitarians, such as Head Start, is called into question.

Segal has a firm grasp on the political climate and prevailing headwinds that the directors of the MISTRA project faced from the outset. She explains that in 1979, when MISTRA was launched, standard psychology textbooks credited “social learning” and “socializing” as the primary factor influencing behavioral development. Segal begins her introduction with a priceless quote from psychologist Walter Mischel:

Genes and glands [sic!] are obviously important, but social learning also has a dramatic role. Imagine the enormous differences that would be found in the personalities of twins with identical genetic endowments if they were raised apart in two different families — or, even more striking, in two totally different cultures.

In fact, studies of identical twins reared apart confirm just the opposite. Segal’s book is full of examples of how various sets of twins, though raised in different households and separated from each other, in some cases for decades, were eerily similar in terms of behavior, interests, outlook, habits, temperament, intelligence, and personality traits. Take the case of the “Jim twins” — Jim Lewis and Jim Springer. The identical twins were separated at four weeks of age and adopted by two families that lived forty miles from each other but each family had been told the other twin had died. Decades later the twins were reunited. Shortly thereafter, Bouchard reached the twins and invited them to the university for further evaluation. This encounter helped launch the MISTRA project. The similarities of the two Jims were phenomenal:

Members of the research team said many times that they did not expect the twins to be as similar as they were. Relying on statistical findings, Bouchard discovered that on most of the twenty-three vocational test categories, the Jims were as alike as the same person taking the same test twice. And their California Psychological Inventory scale scores were so alike that one twin’s profile could be superimposed upon the other’s.

Over the duration of the study — a 20-year period — Bouchard and his research team collected data from “137 reunited sets” of twins (both identical and fraternal twins), which resulted in 150 publications. Academic researchers continue to utilize and analyze MISTRA data in published scholarship.

The range of findings from the Minnesota Twin study project is quite impressive: the genetic influence on individual differences in personality traits is 50 percent and for intelligence, 70 percent  of the variation is caused by people having different genes. Significant genetic effects were found to underlie “intrinsic and general job satisfaction.” And there is a a moderate genetic effect for male sexual orientation (little or none in females), a high genetic correlation between alcohol and drug abuse (0.78), a fifty percent genetic influence on religiosity as well as “negligible shared environmental effect.” The mean heritability for vocational interests was 0.50 with “little evidence that rearing impacted vocational interests.” Other measures of genetic influence spanned an array of psychological and physiological areas: creativity, work values, psychopathology, authoritarianism, social attitudes, mental abilities (general intelligence and special abilities), cognition, happiness, impulsivity and sensation seeking, body size, allergies, cardiac performance, and dental traits.

The comprehensive design of the study, which covered the twins’ travel expenses, lodging and meals for a week, put the twins under rigorous psychological and medical evaluation. Segal estimates that the twins “completed 15,000 questions during the study week.” Methodologically more than one test was used to study many of the twins’ traits. The thoroughness of the study and careful deliberations of the researchers helped to insulate the study from the shortfalls of other twin studies and to preclude critics from nitpicking the findings.

In the chapter on “Personality and IQ,” Segal emphasizes a key point that is often lost in much of the popular coverage of MISTRA over the years. The New York Times and other news organizations stressed the genetic implications of the study’s IQ and personality results, but often in a misleading narrative. As Segal notes,

The Minnesota personality findings were misinterpreted by many. We did not say that parenting does not matter — parents can help shy children feel at ease or help rambunctious kids calm down, as Kagan had shown. One implication of our work was that parents should pay close attention to each child’s unique character traits and nurture each child’s individual interests. Paradoxically, parental fairness seems more likely to come from treating children differently in accordance with their individual behaviors than from treating them alike. Of course, this assumes that family environments are within the normal range (i.e., free of abuse and deprivation).

The bottom line from our data was that growing up together does not make family members alike. Instead, our findings showed that personality similarity between relatives seems to come mostly from their shared genes. Furthermore, environmental effects that are most important in personality development appear to be those that are experienced apart from the family — the nonshared environmental factors; their contributions to the different personality traits were often close to those from genetic factors.

In reading Segal’s account of the MISTRA project, one is struck by the magnitude of the study, the workload of the researchers, and the careful planning and preparation devoted to methodological details in order to avoid quicksand-like traps posed by arch-critics. Such an undertaking required major funding, grants from private and public sources. Of course, hostile adversaries will seize on any thin reed to undermine the standing or credibility of a study with the  ramifications of MISTRA. One such criticism was to complain about the major source of funding: The Pioneer Fund.

The Fund was established in “1937 to advance the scientific study of heredity and human differences.” Over the years it has been an important source of support for landmark research projects in the behavioral sciences. Pioneer Fund grantees have included Nobel Prize winning scientists, a former president of the American Psychological Association (APA), two grantees are among the top five psychologists cited in the scientific literature, other recipients have served as presidents of the British Psychological Society, the Psychometric Society, the Behavior Genetics Association, two were Guggenheim Fellows, others hold top academic honors or are fellows of leading scientific organizations, such as the American Association for the Advancement of Science, the American Psychological Association, Educational Testing Service, and Mensa. One of the initial Pioneer Fund directors, John M. Harlan, a Rhodes scholar, served as a U.S. Supreme Court Justice, nominated by Eisenhower to serve on the nation’s highest court.

Needless to say, the Fund’s track record of underwriting important, top-notch academic research is without question. The fact that Pioneer has also funded projects that explored comparative racial, ethnic, and group differences in psychological traits (intelligence and personality) and educational performance has inflamed righteous fury from egalitarian critics. Pioneer supported William Shockley’s work on racial differences as well as the  work of Arthur Jensen and J. Philippe Rushton on racial differences and general intelligence.

Segal offers a direct and reasonable explanation regarding the “controversy” over accepting Pioneer grants. She notes that the funding from Pioneer placed no conditions or restrictions for accepting their grants. Pioneer provided more than half of the overall total funding ($1,420,551 of $2,330,720) for the project. As Segal points out,

One of the benefits of writing this book has been the opportunity to obtain professional and personal perspectives from each investigator, not just about the science but also about how the science was done. Every colleague stands by the findings, including those who tried to dissuade Bouchard from accepting Pioneer Fund grants. The money partly supported the salaries of many project associates, secretaries, and research assistants, including mine. As Bouchard said in 2009, “If not for Pioneer we would have folded long ago.”

The integrity of MISTRA,  the dedication of the researchers, and the overall significance of the landmark twin studies project have stood the test of time. Despite the strong counter-currents of the prevailing environmentalist dogma of the ’70s and ’80s, and the continuing vociferous opposition of left-wing critics, the MISTRA has contributed to a substantially wider acknowledgement of the importance of heredity as a major source of differences in human behavior. The influence of genes on human behavior can no longer be denied and adoption and twin study projects, such as MISTRA, have made a major impact in this sea-change of direction. Segal’s book is an informative and well-written account of this landmark project.

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