The latest book that I have finished reading is James Flynn’s (1980) Race, IQ and Jensen. This is the earliest work by Flynn that I have ever read, and I can see in it seeds of his later thought.

The heart of the book is a careful examination of the evidence regarding the hereditarian hypothesis that the average difference in IQ across racial groups is at least partially genetic in origin. This is in contrast to the environmentalist hypothesis (which Flynn subscribes to) that average group differences in IQ are entirely environmental in origin.

Direct and Indirect Evidence

Flynn made an important distinction between the direct evidence and the indirect evidence regarding the causes of differences in average IQ across groups. For Flynn,

Direct evidence refers to evidence as to how black and white genes function when they are actually taken our of their usual environmental context, for example when both are put into a neutral environment, or when white genes are put into a black environment, or vice versa. . . . Indirect evidence refers to . . . attempts to predict what would happen if black and white genes exchanged environments, whether this is done by weighing the influence of specific environmental factors . . . or by weighing the influence of environment in general against genetic factors in general.

Flynn (1980, p. 74)

In other words, Flynn (1980) saw the best evidence as occurring when “black genes” and “white genes” [sic] are outside of the typical “black” and “white” environments, respectively. According to Flynn, the best direct evidence comes from admixture studies and transracial adoption studies. The best indirect evidence is from the mathematical relationship between within- and between-group heritability and the fact that nobody can propose a credible X-factor (which is a unique proposed single-race environmental variable that lowers one group’s IQ scores uniformly).

I agree with Flynn that the direct evidence should overrule the indirect evidence. He wrote a thorough analysis of both types of evidence as they existed at the end of the 1970s. In Flynn’s assessment, the indirect evidence favored the hereditarian hypothesis, but the direct evidence favors the environmentalist hypothesis. But because direct evidence trumps indirect evidence, environmentalism should be the favored viewpoint.

A Fine Piece of (Dated) Scholarship

For its time, Race, IQ, and Jensen is a fine piece of scholarship. Flynn is a committed environmentalist, but he doesn’t let his preferences cloud his judgment of evidence.

Flynn was scrupulously fair to Jensen. Chapter 2 is the best summary of Jensen’s viewpoints that I have ever read (outside of Jensen’s own works). Flynn stressed that Jensen is not a racist in any way, and Flynn recognized the strength of some of Jensen’s arguments and saw them as worthy of answering with data, instead of derision. After over a decade of being misrepresented and villified since his Harvard Education Review (Jensen, 1969), article, Flynn’s (1980) book must have been a refreshing change for Jensen.

Moreover, Flynn avoided the specious reasoning that most environmentalists subscribed to at the time. For example, he chastises his fellow environmentalists for using Lewontin’s (1970) seed analogy (which I have summarized before) as evidence in favor of the environmental hypothesis:

Far too many of Jensen’s critics have not taken up the challenge to refute him in any serious way, rather they have elected for various forms of escape, the most popular of which has been to seize on an argument put forward by the distinguished Harvard geneticist Richard C. Lewontin. . . . It is easy to understand the appeal of Lewontin’s argument. . . . The range of scholars who have used some version of the above argument against Jensen is quite extraordinary . . . For some, Lewontin’s argument is so self-evident and so significant that whether or not a scholar accepts it is the measure of whether he has anything worthwhile to say about race and IQ! . . . After reading these scholars, it comes as something of a shock to realize that Lewontin’s example does not at all show the irrelevance of high h2 [heritability] estimates to finding an explanation of between-population differences. . . . the real message of Lewontin’s example is that we can ignore high h2 estimates only if there exists a highly specific and highly unusual set of circumstances.

Flynn (1980, pp. 54, 56, 57, 58-59).

This was typical of Flynn’s (1980) tone with his fellow environmentalists. His patience with faulty reasoning and wishful thinking is palpable in many sections of the book.

Me with James Flynn in 2017 in Montreal.

Most of the book is spent carefully analyzing the direct evidence regarding the causes of average differences in IQ across African Americans and European Americans. Flynn makes a convincing argument that the transracial adoption studies at the time (Scarr & Weinberg, 1978; Tizard, 1974), while not completely unambiguous, supported the environmentalist position more than the hereditarian argument at the time. I agree.

Flynn was also extraordinary thorough in analyzing the admixture studies. Surprisingly, he dismissed the importance of the blood group studies (Loehlin et al., 1973; Scarr et al., 1977), though he found the Witty and Jenkins (1936) admixture study persuasive, even though the method of determining admixture was merely to ask the subjects’ families how much European heritage the children had. Flynn also found the Eyferth studies of German children fathered by White and Black American soldiers to be persuasive, and he wrote a 43-page appendix analyzing the data and estimating the IQs of the fathers of the subjects.

The biggest drawback of Race, IQ, and Jensen is that it is outdated. A careful dissection of imperfect 1970s studies is not necessary now. Forty years ago, it would have been the best source for understanding the controversy around the causes of average difference in IQ across racial groups. Today, the book’s usefulness is more limited.

An Unheeded Plea

It is a shame that more people didn’t read Flynn’s (1980) book at the time. In the 1980s, it was only cited 83 times, according to Google Scholar. The low level of interest (for a scholar of Flynn’s stature) is a shame because the book is a road map for strengthening the environmentalist evidence regarding the causes of differences in average IQ across races. Among Flynn’s suggestions:

  • Concentrate on accumulating direct evidence and de-emphasize the indirect evidence (pp. 74-75).
  • Improve transracial adoption studies, especially by gathering IQ data for the biological parents of adoptees (p. 109).
  • Stop relying on faulty reasoning (like Lewontin’s seed analogy), defeated arguments (like claims that the race of the intelligence test administrator causes lowered scores for African American examinees), or wishful thinking (p. 54).
  • Don’t look for X-factor that uniformly lower one group’s IQ scores while keeping the other groups’ scores intact and instead search for variables that can exert a partial influence on IQ for low scoring groups (pp. 216-218).
  • Replicate studies that support the environmentalist viewpoint (pp. 101, 180).
  • Investigate whether heritability values are lower in some environments or some groups–a hypothesized phenomenon now called the Scarr-Rowe effect (pp. 126-127).
  • Identify a stable, realistic within-group heritability estimate for African Americans (p. 158).
  • Collect better data about the pre-natal and post-natal environment of children, especially African Americans (pp. 166-167).
  • If researchers do posit gene-environment interactions, those interactions should be specific and testable (p. 175).

And Flynn’s most important advice:

. . . whatever evidence we accumulate will not be conceded to be relevant if, as has been generally true up to now, we do not control for genetic factors.

Flynn (1980, p. 181)

Unfortunately, the environmentalists ignored Flynn’s advice. Fast forward to the 21st century, and what do we see? The environmentalist position looks almost the exact same as it did in 1980. According to environmentalists, there is still hope for an X-factor (e.g., Kaplan, 2015), and the same 1970s admixture studies are being cited authoritatively (e.g., Nisbett, 2005). One-quarter of introductory psychology textbooks still use Lewontin’s (1970) seed analogy to dismiss the possibility of genetic causes of between-group differences in IQ (Warne et al., 2018).

The only way the environmentalist argument has advanced since 1980 in a way Flynn had suggested is the topic of Scarr-Rowe effects. Turkheimer et al. (2003) published a study showing that heritability was zero in young American children living in poverty. But even this evidence has been weakened since. That study is clearly an outlier (compare, for example, Figlio et al., 2017), and the best evidence indicates that heritability of IQ within large American racial groups is remarkably similar (Pesta et al., 2020). So, even on this front, the environmentalist argument had a temporary advance that has since resulted in a retreat.

Even the strongest environmentalist evidence (based on Flynn’s opinion in 1980) has since weakened. The follow-up of the largest transracial adoption study showed a decrease in IQ for African American children adopted by White parents (Weinberg et al., 1992), a blow to the environmental hypothesis. Moreover, with the advent of DNA ancestry tests, all the admixture studies Flynn (1980) analyzed are obsolete.

Forty years later, the environmentalists camp has little to show for their efforts. On the other hand, the hereditarians did the research Flynn suggested. They conducted the admixture studies. They collected heritability values for different groups. They created the genetically sensitive studies. The hereditarians spent 40 years strengthening their arguments and their data, while the environmentalists squandered their time. Now, the indirect evidence still supports the hereditarian hypothesis, and much of the direct evidence does, too. As a result, a majority of 21st century intelligence scholars subscribe to the hereditarian hypothesis (Rindermann et al., 2020).

While I do not know for sure, it seems likely that Flynn is not surprised by this development. As he wrote in Race, IQ, and Jensen:

At times there seems to be a malevolent invisible hand at work in this area which guarantees that really important research, even research relatively easy to do, will never be replicated.

Flynn (1980, p. 165; see also p. 192).

James Flynn is a modern-day Cassandra. He knew exactly what research was needed to support the environmentalist perspective, but no one heeded his call. As a result, the environmentalists are in the weakest scientific position that they have experienced in living memory. If the environmentalists are uncomfortable with the amount and strength of evidence supporting a partial genetic influence on average IQ differences across racial groups, they only have themselves to blame.

Cassandra, painted by George Romney. Source: Wikimedia Commons.

Using the Road Map–Finally

Although the hereditarians got a head start, it is not too late for the environmentalists to use Flynn’s road map. The first step is to start gathering data and designing the studies Flynn suggested. A new transracial adoption study that includes IQ scores for biological parents would be an excellent goal. Environmentalists should also conduct their own admixture studies with modern methods of ascertaining ancestry.

Also, I suggest that environmentalists cultivate the same attitude of respect towards the hereditarian hypothesis that Flynn had. Flynn respected Jensen (Flynn, 2013), and did not fall into easy patterns of moralistic thinking. Indeed, we should all endeavor to be like James Flynn.


Figlio, D. N., Freese, J., Karbownik, K., & Roth, J. (2017). Socioeconomic status and genetic influences on cognitive development. Proceedings of the National Academy of Sciences, 114(51), 13441-13446.

Flynn, J. R. (1980). Race, IQ, and Jensen. Routledge & Kegan Paul.

Flynn, J. R. (2013). Arthur Robert Jensen (1923–2012). Intelligence, 41(2), 144-145.

Jensen, A. R. (1969). How much can we boost IQ and scholastic achievement? Harvard Educational Review, 39(1), 1-123.

Kaplan, J. M. (2015). Race, IQ, and the search for statistical signals associated with so-called “X”-factors: environments, racism, and the “hereditarian hypothesis.” Biology & Philosophy, 30(1), 1-17.

Lewontin, R. C. (1970). Race and intelligence. Bulletin of the Atomic Scientists, 26(3), 2-8.

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Nisbett, R. E. (2005). Heredity, environment, and race differences in IQ: A commentary on Rushton and Jensen (2005). Psychology, Public Policy, and Law, 11(2), 302-310.

Pesta, B. J., Kirkegaard, E. O. W., te Nijenhuis, J., Lasker, J., & Fuerst, J. G. R. (2020). Racial and ethnic group differences in the heritability of intelligence: A systematic review and meta-analysis. Intelligence, 78, Article 101408.

Rindermann, H., Becker, D., & Coyle, T. R. (2020). Survey of expert opinion on intelligence: Intelligence research, experts’ background, controversial issues, and the media. Intelligence, 78, Article 101406.

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Scarr, S., & Weinberg, R. A. (1976). IQ test performance of Black children adopted by White families. American Psychologist, 31(10), 726-739.

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Turkheimer, E., Haley, A., Waldron, M., D’Onofrio, B., & Gottesman, I. I. (2003). Socioeconomic status modifies heritability of IQ in young children. Psychological Science, 14(6), 623-628.

Warne, R. T., Astle, M. C., & Hill, J. C. (2018). What do undergraduates learn about human intelligence? An analysis of introductory psychology textbooks. Archives of Scientific Psychology, 6(1), 32-50.

Weinberg, R. A., Scarr, S., & Waldman, I. D. (1992). The Minnesota Transracial Adoption Study: A follow-up of IQ test performance at adolescence. Intelligence, 16(1), 117-135.

Witty, P. A., & Jenkins, M. D. (1936). Intra-race testing and Negro intelligence. The Journal of Psychology, 1(1), 179-192.