Bad Science Revisited: “The Bell Curve” Turns 30

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“The inheritance of intelligence is probably the most controversial topic in the whole of science,” wrote geneticist Adam Rutherford, “and when it is combined with the study of population differences, evolution, and race, there we have the prospect of a perfect storm.”

This September will mark 30 years since the appearance of a widely publicized and controversial entrance into the storm: The Bell Curve: Intelligence and Class Structure in American Life. Its authors were Harvard University animal-learning psychologist Richard Herrnstein and conservative U.S. political scientist Charles Murray. Herrnstein passed away shortly before the book was published in 1994. Murray has been active since then. In their 800+ page book, they argued that IQ tests measure “intelligence” and that IQ is a strong predictor of school and career achievement. They claimed that IQ is “substantially heritable” (roughly 60%)—a long-disputed yet standard conclusion found in many psychology textbooks.

A normal distribution curve appears on a tablet screen

The authors, however, went further by claiming that IQ is largely unchangeable, and by reviving the old IQ hereditarian argument that “dysgenic” effects of higher birth rates among people and groups with lower IQ scores threaten to reduce intelligence levels in the U.S. “Something worth worrying about is happening to the cognitive capital of the country,” they wrote. Without referring to them as eugenic, they supported policies encouraging the reproduction of people with high IQ scores and discouraging the reproduction of people with low IQ scores. In Chapter 21, they painted a bleak picture of the future, where differential reproduction patterns among what they called the genetically “dull” and the “cognitive elite” would lead to the creation of a U.S. genetic “custodial state” that would resemble a “high-tech and more lavish version of the Indian reservation for some substantial minority of the nation’s population.” For Herrnstein and Murray, such an outcome would mainly be the result of heredity, not political decisions and policies causing greater economic inequality and poverty. Inequality by political “design,” as one group of Bell Curve critics described it.

The most controversial aspect of The Bell Curve was Herrnstein and Murray’s position on IQ racial (ethnic) differences. “It seems highly likely to us,” they wrote, “that both genes and the environment have something to do with [IQ] racial differences” between U.S. Whites and Blacks (African Americans). Like psychologist Arthur Jensen before them, they claimed that genes for cognitive ability play a role in causing higher White versus Black group IQ differences. They were only unsure about what the gene-environment “mix” might be.

I recently co-authored a preprint article with Ken Richardson, formerly Open University UK (now retired), entitled The Bell Curve at 30: A Closer Look at the Within- and Between-Group IQ Genetic Evidence.” We focused on the genetic research cited in the book, including some relevant history of the IQ genetics debate. The larger question of whether or how heredity influences human intelligence was beyond the scope of our article.

Like many previous reviewers, we concluded that Herrnstein and Murray produced no valid evidence that the IQ “gap” between ethnic groups is caused in any part by genetic factors. IQ hereditarians often say the existence of the gap is undisputed and that the debate centers only on its causes. However, the gap’s existence is disputed by those who argue that “race” is invalid as a biological variable and that IQ tests don’t measure “intelligence.” Moreover, some argue that IQ tests are designed to reproduce assumed ethnic and class differences in intelligence.

In addition, unlike most previous reviewers, we concluded that Herrnstein and Murray produced no valid evidence that genes influence within-group IQ score differences. The key evidence they cited consisted of “twins reared apart” studies and, to a lesser extent, family correlations, reared-together twin studies, and adoption studies. Aided by concepts developed in science’s ongoing “replication crisis,” we argued that the genetic findings reported in these studies do not hold up under critical examination due to environmental confounding, a reliance on uncertain or false assumptions and concepts, the use of questionable research practices (QRPs), and other problem areas. In the language of psychometrics and behavioral genetics, we argued that Herrnstein and Murray presented no valid evidence in support of above-zero IQ heritability. This conclusion, of course, automatically invalidates claims about genetic group differences.

Because IQ molecular genetic research was at an early stage in 1994, Herrnstein and Murray did not cite any IQ gene (genetic variant) associations or discoveries. The behavioral “candidate gene” era, also at an early stage in 1994, turned out to be an expensive and embarrassing “flop.” For example, the title of a 2012 article read, “Most Reported Genetic Associations with General Intelligence Are Probably False Positives.” The subsequent genome-wide association (GWAS) and polygenic score studies Murray promoted in his 2020 book Human Diversity are subject to low scores, environmental confounding, and other significant problems described by the scholars we cited in our article.

We showed that the “Flynn effect” finding of “massive” IQ score gains over time (3-5 points per decade), which Herrnstein and Murray discussed and did not dispute, undermined the central Bell Curve arguments. Moral philosopher and IQ researcher James Flynn called the world’s attention to the fact that, due to these gains, IQ test creators periodically revise their tests to make them more difficult. They do so to maintain a mean score of 100 and a bell-shaped score distribution. Based on 1948-era IQ tests, in 2008 Flynn calculated that U.S. Blacks of 2002 would have outscored U.S. Whites of 1947-48 by 4.3 IQ points (Full-Scale Black IQ 104.3 versus White IQ 100). Flynn proposed selecting a representative sample of contemporary U.S. Blacks and giving them the old IQ test to confirm his calculation. “Frantic appeals,” he discovered, “have not located anyone interested.”

Theoretically, using the same IQ test version and due solely to the Flynn effect, if previously studied reared-apart identical (MZ) twin pairs had been born two generations apart, the younger twins would have scored about 15 points higher than their genetically identical co-twins. The Flynn effect (plus several other shared birth-cohort environmental influences we described) indicates that a good chunk of the reared-apart identical twin IQ correlations Herrnstein and Murray cited as the “most unambiguous” evidence in favor of strong genetic influences on IQ can be explained not by the genes twins share, but by the birthday they share. The Flynn effect sent a wrecking ball into Herrnstein and Murray’s already crumbling within-group IQ genetic evidence, and supplied the final nails in the coffin of their genetic ethnic and class differences in cognitive ability claims.

The question remains why, despite three decades of criticism, the book remains “alive.” One answer is that although the Bell Curve arguments rested on massively flawed research, its misguided message is needed to maintain and support institutional racism and neo-colonialism, and to inspire “race scientists.” In 2023, a former U.S. President, running for reelection, spoke of immigrants as supposedly “poisoning the blood of our country.” A few months later, a major U.S. poll found that almost half (47%) of registered voters endorsed this statement. Even more reason to embark on yet another in-depth critical examination of this book.

In 1976, evolutionary biologist Richard Lewontin wrote that critics had found in IQ genetic research “a pattern of shoddiness, carelessness, miserable experimental design, misreporting, and misrepresentation amounting to a major scandal.” Four years later, sociologist Howard Taylor defined “the IQ game” as IQ genetic researchers’ “use of assumptions that are implausible as well as arbitrary to arrive at some numerical value for the genetic heritability of human IQ scores on the grounds that no heritability calculations could be made without benefit of such assumptions.” The Bell Curve continued both dreadful traditions and helped disguise politically and even militarily imposed social, political, economic, and international inequality as biological inequality.

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Link to the full preprint article “The Bell Curve at 30: A Closer Look at the Within- and Between-Group IQ Genetic Evidence”: https://osf.io/preprints/psyarxiv/jz7ku

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Mad in America hosts blogs by a diverse group of writers. These posts are designed to serve as a public forum for a discussion—broadly speaking—of psychiatry and its treatments. The opinions expressed are the writers’ own.

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24 COMMENTS

    • Jay (and I, and others) have argued that heritability scores for human beings are meaningless. None of the studies (family studies, twin studies, and adoption studies) used to measure “heritability” control for environmental variation. All are fatally flawed, and repeating the same fatally flawed studies gets us no closer to the truth.

      The fundamental assumption underlying family studies — that familial equals genetic — is false.

      The fundamental assumption underlying twin studies — the equal environment assupton — is false.

      The fundamental assumption underlying adoption studies — that adoption randomizes environmental variation — is false.

      Plus such studies do not allow for genotype-environment interactions, which for complex traits such as IQ probably are the rule rather than the exception.

      The only legitimate use of heritability scores is predicting the results of controlled breeding experiments on plants and animals in factory farms, where environmental variation can be assumed to be negligible. And even there, the heritability score applies only to that particular population of plants or animals on that particular factory farm. It is not a “nature-nurture” ratio.

      Psychologists and psychiatrists have unthinkingly applied this concept to human beings, who experience many orders of magnitude more of environmental variation and can make conscious choices to change their environment.

      I know of no benefit that has ever accrued to mankind by calculating heritability scores for human beings. It’s time to move on.

      Regardless of what you think of them morality of eugenics programs, that fact is they don’t work.

      If a trait is caused by a dominant gene, you’ll never get its frequency below the mutation rate, and it is unlikely to be very much above that in the first place.

      If a trait is caused by a recessive gene, it is easy to show mathematically that it would take hundreds of years of selection against the homozygote to make a dent in that gene’s frequency. And if you select against the heterozygote, you’d have to kill off everybody, several times over, because we all have some unpaired bad genes.

      And for complex traits like IQ, forget it. There are too many potential confounding factors to make it feasible to make any significant directed changes in the human gene pool, within any meaningful time horizon.

      Let’s do a better job of shepherding the gene pool we have.

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    • No. As stated in the MIA article and in the full preprint article, “The larger question of whether or how heredity influences human intelligence was beyond the scope of our article.” We focused our analysis mainly on the supposed within-group and between-group “IQ heritability” presented in The Bell Curve.

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      • Although the new article focuses mainly on evidence cited in The Bell Curve, I did address the larger question of hereditary influences on cognitive ability in a 2023 MIA article, an interview with Mary Boyle: https://www.madinamerica.com/2023/06/mary-boyle-interviews-jay-joseph/

        “Psychiatric and behavioral geneticists argue that heredity plays an important role in producing “individual differences in behavior.” To understand how these differences arise, they say we should focus on reared-together twins, reared-apart twins, adoptees, brains, genes, IQ scores, biological-relative IQ correlations, “personality,” a range of statistical modeling techniques, “mental disorders,” crime statistics, GWAS hits, polygenic risk scores, and heritability estimates. Supporters of this approach sometimes depict those who focus on environmental causes of behavioral differences as suggesting that people are born as psychological “blank slates.” Steven Pinker attributed this view to environmentalists in his 2002 book The Blank Slate: The Modern Denial of Human Nature, and it has continued since then.

        However, so-called “blank slatism” is a straw man because few who focus on environments hold such views as they relate to cognitive and other abilities and temperament. They usually argue that while there may well be inborn differences among people in these areas, it is perinatal, family, social, cultural, religious, educational, geographical, and political environments (including oppression) that together play a decisive role in shaping human behavior and abilities, and that focusing on “individual differences” and problematic heritability estimates implies limited changeability and distracts our attention from the need to improve or radically change these environments.”

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  1. Jay:

    I’ve just finished reading the full preprint. Great job, as usual. With pin-point accuracy you have devastated genetic determinist views of human behavior.

    Along with the meaningless concept of “mental illness,” it’s time we laid the meaningless concept of “race” to rest for good.

    Instead of obsessing over the supposed genetic deficiencies of “those people,” let’s start doing a better job of shepherding the gene pool we have.

    Pat

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  2. We know the conditions human beings need to thrive. It’s not rocket science. Children need first and foremost to be sheltered and protected from harm. They need to fed wholesome foods in appropriate quantities, they need clear boundaries, consistent discipline, and LOTS of outdoor free play time every day. Barring the tiny minority of children born with rare monogenetic disorders or chromosomal aberrations, show me a child who is provided with all these things who fails to thrive.

    Let’s work on making these conditions available to all children. Blaming our problems on our supposedly faulty gene pool is a preposterous distraction from doing that.

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  3. Jay and Patrick:
    I will need to go further and reread the article! Though in living in Louisville when the Bell Curve articles and stream of discussion occurred 30 years ago and before, the local well known civil rights activist would take to task the author. Meaningless? No, though what is the better place to realize gainful understanding for the role of stats in application as well as theoretical advancement? For while protests could be stirred up, the challenge to the laws aligned with civil rights through the Federal Courts, just who can understand civil rights and the capacity to recover and deeply understand the roles of piercing the corporate veil (see Adam Winkler) while coming to understand understanding as work/play in need of appropriate capitalization for LIFE? (See Robert Reich (The System).

    Hence, can you elaborate a little more on how and why there is only a Bell Hill that ignore a Bell Hell? The collection of data to be mapped along the lines of evolved academia when explained by W. Edwards Deming unveils many flaws as well as infinite opportunities for improvement.

    And from my research, the schizophrenia that can emerge in an altered state is recognized as one of the more creative spaces to be in, though can be a challenge to 1) accept one’s self, 2) accept what is happening outside of self and 3) realize systemic change for others since threads of community still abound. Perhaps the madinamerica gathering is not so mad after all for the challenge to broaden the understanding in the course of realizing the deepest of justice for all.

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    • Have you heard that iq tests are made to target the mechanical mind such that these people get high iq scores and foremostly misogynist in that women have been historically denied development in these areas…as in electronics etc the male dominated fields…in this bias that only addresses one form of intelligence that historically has been male.

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  4. Absolutely awesome essay, thank you very much, indeed!

    Since coming to the US from Ireland (where our constitution, in my opinion, effectively stated that all citizens shall be considered equal, apart from those clearly not) 2009, I have asked many Americans, almost every one of them a perfect stranger, if we are all equal.

    The only consistent answers I have received have been Huh?, frequently, and No!, twice.

    I’ve had Equal in God’s eyes (or was it Eyes?) and In opportunity more than once.

    I have not redone single, solitary, satisfactory answer – meaning, I suppose, one which fully coincided with my own very considered and not particularly humble opinion/s.

    One guy, interestingly, probably following a Huh?, when, as usual, I had pointed out that the Founding Fathers had pointed out that the fact that we had all been, and presumably would continue to be created “equal,” and or BUT that this was supposedly so “self-evident” as to justify or require explanation, however novel a concept it might seem, that the Constitution and all laws, I guess, were based on this entirely religious notion…replied that, when those Fathers asserted that we – “white” men, at least(!!!!!!!) ; were all all “created equal,” merely meant that none of us was/were created with a divine, royal right to rule.

    My opinions, for what they are worth as priceless treasures, are that we all equal as immortal, infinite, “divine” beings, neither created nor begotten, but, as it seems Emperor Constantine managed to coerce his First Council of Nicaea to agree that ONLY Jesus of Nazareth and none of the rest of us, not even Julius Caesar, were “of one being/substance with The Father.”

    I believe we are equal in wishing to serve one another, and im being willing sacrifice equally in human/animal/divine suffering over however many human lifetimes it takes: one former president, in his apparent misery and frustration, id therefore much like…Jesus in his!!!!!!!

    Praying he may soonest find relief, and likewise all of us, by rediscovering how best to use our supreme and supremely equal though varied intelligence, to most joyfully serve all, and with heart- and soul-felt thanks to Jay Joseph, Jesus, MIA and all our former presidents, Founding Fathers and ALL,

    Tom.

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  5. …….PS: And, while the wisdom of certain “Native American s” as Chief Seattle strikes me as unsurpassable, no doubt, regardless of any genes, we are all nowadays rapidly becoming more infinitely intelligent – unconditionally loving – as our egos are transmuted to smarts in the fires of our emerging Consciousness….

    Thank you, ALL, again!

    Comfort and joy, and “God” rest ye all merry!

    Tom.

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  6. Jay Joseph has spent decades successfully debunking “hereditarian” viewpoints, especially the fake science of “twin studies.” In this MIA article, he asks: “The question remains why, despite three decades of criticism, the book remains “alive.” One answer is that although “The Bell Curve” arguments rested on massively flawed research, its misguided message is needed to maintain and support institutional racism and neo-colonialism, and to inspire “race scientists.”

    Every kind of oppression requires an ideology that shifts the blame away from the oppressors to the oppressed. For many centuries now, “biological reductionism” has served as this ideology: our mistreatment of a particular class of people is because of the inherent characteristics of that class: It’s their fault that we are forced to treat them this way.

    With psychiatry, biological reductionism claims that the people we are involuntarily diagnosing, committing and treating must be treated this way because they are biologically different and incapable of a) understanding their true illness, and b) changing their behavior in the ways that we demand.

    The Big Lie of psychiatry is that people who behave in ways society finds offensive are considered biologically different and inferior. Psychiatry per se is now 200 years old and has yet to provide any substantial, conclusive scientific evidence to support its main thesis.

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  7. If those among us with Down or Down’s syndrome are more unconditionally loving than the rest of us, perhaps they are more intelligent than us, and perhaps there may be perceived to be a genetic correlation and/or cause for this & as well as demonstrating how foolish our “intelligence tests” truly are?
    But, to the extent that such human beings, like the rest of us, are simply always doing their best and, like any blade of grass pushing up through cracked asphalt, following their nature, and being true to themselves as we all are, perhaps even they may not be our superiors, either?
    On Our Unequivocal Ultimate Infinite Equality:
    Confucius, I guess: YES, HE knew:
    “Young man who fancy pretty nurse
    He must be patient, too!”
    Lao Tzu? Totally knew!
    Caesar? – Julius? – I’d say, too.
    Rumi? EViidently knew.
    Carl Jung? Yep! Exposed it, too.
    And Archbishop Des Tutu.
    Jesus, how HE preached it! – PHEW!
    Who understood him? Few! Few! Few!
    The Buddha, he most clearly knew.
    Buddhists, tho’? Perhaps? Some, too?
    The Sioux? TOTALLY! Told it, too…
    Very much as gnostics do.
    Descartes and then John Paul Sartre
    Don’ talk to me about those two:
    Blew it! Blew it! Merde de DIEU!
    ?SOME? dear old Founding Fathers – WHO!?
    IF they did, they chose not to
    Share it with all doubters who
    “Self-evidence” would quite eschew
    So that we might now live to rue
    Their desperate refusal to
    ‘Lucidate for motley crew
    How candidates who hatred spew
    Can be praised by those who view
    Them and selves as saintly few..
    But that, maybe, WE ought, too?!
    References:
    Tzu, Lao: “At the center of your being you have the answe: You know who you are and you know what you want!”
    Caesar, Julius: Please see what he wrote of the druids under “Philosophy “ here: https://en.m.wikipedia.org/wiki/Druid
    Rumi, Jalal al-Din Muhammad: ‘This is what is signified by the words Anā l-Ḥaqq, “I am God.” People imagine that it is a presumptuous claim, whereas it is really a presumptuous claim to say Ana ‘l-‘abd, “I am the slave of God”; and Anā l-Ḥaqq, “I am God” is an expression of great humility. The man who says Ana ‘l-‘abd, “I am the servant of God” affirms two existences, his own and God’s, but he that says Anā l-Ḥaqq, “I am God” has made himself non-existent and has given himself up and says “I am God”, that is, “I am naught, He is all; there is no being but God’s.” This is the extreme of humility and self-abasement.’ https://en.m.wikiquote.org/wiki/Rumi
    Jung, Carl: “I don’t believe….I KNOW!” “In all chaos, there is a cosmos; in all disorder, a secret order!” Etc.
    Tutu, Desmond: *Be nice to the whites, they need you to rediscover their humanity.”
    Of Nazareth, Jesus: “You are the Light of the World!”
    Of Nazareth, Jesus, acc. to Luke, 17:21:”Neither shall they say, ‘Lo here!’ or, ‘lo there!’ for, behold, the kingdom of God is within you!”
    Of Nazareth, Jesus, acc. to Gnostic Gospel of Thomas ‘Jesus said, “If those who lead you say, ‘See, the Kingdom is in the sky,’ then the birds of the sky will precede you. If they say to you, ‘It is in the sea,’ then the fish will precede you. Rather, the Kingdom is inside of you, and it is outside of you.”’
    Buddha, Gautama’ “Enlightenment is the end of suffering!”
    Sioux, A Story from: ‘The Creator gathered all of Creation and said :
    “I want to hide something from the humans until they are ready for it. It is the realization that they create their own reality.”
    The eagle said, “Give it to me, I will take it to the moon.”
    The Creator said, “No. One day they will go there and find it.”
    The salmon said, “I will bury it on the bottom of the ocean.”
    “No. They will go there too.”
    The buffalo said, “I will bury it on the Great Plains.”
    The Creator said, “They will cut into the skin of the Earth and find it even there.”
    Grandmother Mole, who lives in the breast of Mother Earth, and who has no physical eyes but sees with spiritual eyes, said, “Put it inside of them.”
    And the Creator said, “It is done.”’
    Sioux, Dakota: *We will be forever known by the tracks we leave.
    Seathl, of Susquamish, Chief: https://www.csun.edu/~vcpsy00h/seattle.htm
    When is a square equal to a circle? When infinite.
    So are all presidents, presumably, too – equal as immortals – and perhaps as mortals, too – iif ONLY they could all remember that!
    “What we do in life echoes in eternity!” – Maximus Decimus Meridius/Russell Crowe as Gladiator in “Gladiator.”
    “Death hangs over you. While you live, while it is in your power, be good. Think of yourself as dead. You have lived your life.”
    – Marcus Aurelius, from whom also:
    “It is not death that a man should fear, but he should fear never beginning to live.”
    …by learning to truly GIVE!
    “Those who WOULD govern us are the last people we should ever trust TO government us!” – John Cleese?
    Me? I pray for Messrs. Putin and Trump, and for their enlightenment, and for the enlightenment of their and or our worlds, and for the empowering faith that stranger things have happened and must happen, and that we all can and will all help MAKE them happen!
    Peace!

    Tom.

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  8. Big thanks Jay Joseph! Screw the I.Q test, it’s as misleading an indicator of intelligence as it is a distortion of intelligence; a veritable political weapon masquerading as a social tool.

    On a personal note-to Keith’s and Patrick’s and others comments: my IQ tested at 86 when I was 12. When I told my therapist this “fact” when I was 37 (I did so in an attempt to get him off my back about about my living and “working” below my intelligence), he made a wager that made it worthwhile for me take the dam test (with a colleague of his). If my IQ came back under 120 I won, and if over 120 I lost: I lost. But my point here is that I took the IQ test as an abused kid on Thorazine, and that fact registered not one whit with “anyone” (teachers, etc.), save only heap more shame on me. I can more than imagine the legions of abused or developmentally marginalized kids that, over the past 50 years, were further dumped upon by 2 (as the sum usually is) bloody meaningless digits…

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  9. Hi Patrick, if your referring to my comment, I actually did share my story in a ‘Personal Story” from an April 9th 2021 post (Bearing False Witness: Childhood Psychiatry, Trauma, and Memory). That said, perhaps a more well written story/blog or two may be more informative/helpful for readers surrounding the issues and challenges generally undertaken here at MIA?

    But, FWIW, if this subject matter is of further interest, I recommend the memoir “Life Inside” by Mindy Lewis. Lewis was a 15 y/o kid diagnosed schizophrenic in 1967, drugged with Thorazine for 2 and a half years (or was it longer?) on a NYC psych-ward. The problem was that not only did Lewis never (remotely) display symptoms “associated” with schizophrenia, but that the “counternarrative” life she had after leaving that psych ward a testament to the breathtaking institutional incompetence of psychiatry, as well as the “human” cost left in its wake…

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