“The impulse to think that environmental sources of differences are less threatening than genetic ones is natural but illusory.” Charles Murray
“Convictions are more dangerous enemies of the truth than lies.” Friedrich Nietzsche
Recently, the popular online political outlet Vox published an article in response to Charles Murray’s interview on Sam Harris’s “Waking Up”1 podcast that illustrates the insidious effect ideology can exert on science. The article, written by a group of esteemed scholars, Eric Turkheimer, Kathryn Paige Harden, and Richard E. Nisbett, contended that Murray is still “peddling junk science” about race and intelligence, thereby duping otherwise critical scholars like Harris with pseudo-scholarship and sophistry. The article attempts a moderate, scientifically sound criticism of hereditarianism (i.e., the contention that at least part of the Black-White IQ gap is genetic). Unfortunately, the result is a tendentious and ideologically skewed attack on Murray that forwards cherry picked studies, ignores copious data, and dismisses the impressive explanatory power of hereditarianism with a wagging finger of moral disapproval.
Turkheimer et al did not dispute many of the most important points discussed in the podcast. For instance, they accepted that intelligence is real, that it can be measured, that it predicts important life outcomes, that it is heritable (i.e., individual differences in intelligence can be explained, in part, by differences in genes), and that it varies among racial groups.2 What they did dispute, however, is the assertion that some of the IQ gap between Blacks and Whites in the United States (Blacks score about 15 points lower than Whites on IQ tests) is likely accounted for by differences in genes. And, more specifically, they contended that Murray ignored important evidence and ran roughshod over the contradictory data he did discuss. To make their case, the authors forwarded four pieces of evidence “insufficiently addressed” in the podcast that, according to them, refute (or cast significant doubt on) hereditarianism: (1) the shrinking IQ gap between Blacks and Whites; (2) the Flynn effect; (3) the large IQ gains from adoption; and (4) the fact that the heritability of IQ is lower in disadvantaged American children than in advantaged American children.
We will address all four of these points below, then forward theory and evidence that Turkheimer et al ignored, and end by briefly discussing ethical concerns about studying and speaking candidly about race differences in intelligence.
The Shrinking IQ gap between Blacks and Whites
Turkheimer et al claimed that the Black-White IQ gap is “now closer to 10 points” than 15 points. They also claimed that the academic achievement of Blacks has “improved by about one-third standard deviation [i.e., 5 IQ points] in recent decades.” Although there is some evidence that the Black-White IQ gap did narrow in the 20th century, the claim that the IQ gap is now 10 points is based largely on the results of a single, heavily criticized paper, and is not consistent with the vast majority of the evidence.
For example, Murray conducted analyses of the Woodcock-Johnson cognitive test batteries and found no decrease in the Black-White gap for those born after the 1960s (and, in fact, found a slight increase in this gap since the 1960s). He found similar results using data from the National Longitudinal Survey of Youth. Other scholars, examining the available evidence up to 2005 in their response to claims of a narrowing Black-White gap, concluded, “…the best evidence of the Black-White convergence over the past 100 years is between 0 and 3.44 IQ points…”
On achievement, the Black-White gap narrowed during the 20th century, but multiple indicators of educational achievement provide convergent evidence that the gap has stopped narrowing and, in some cases, is widening. Among the more optimistic assessments, Rindermann and Thompson, analyzing data from the National Assessment of Educational Progress (NAEP), documented that the Black-White gap declined from 16.33 to 9.94 IQ points between 1971 and the early 1990s. However, they also noted that the gap has been stable since the early 1990s. Similar findings, with somewhat smaller convergences between Blacks and Whites, have emerged for the SAT, the GRE, and educational attainment, more broadly. Summarizing research on cognitive ability across the 20th century in employment and educational settings, Roth and colleagues concluded, “As a whole, these studies suggest that there are observed gains for both groups [Blacks and Whites], but the reduction in the between-group difference is either small, potentially a function of sampling error, or nonexistent for highly g loaded instruments.” (p. 323).
So, although it is reasonable to argue that the Black-White IQ gap shrunk a bit in the early 20th century, the claim that the IQ gap is now 10 points is only supported by a few data points. It seems to us more reasonable to contend that the IQ gap has stabilized near 12-15 points.
The Flynn Effect
Turkheimer and colleagues asserted that IQ scores have increased 18 points in the US from 1948 to 2002. They noted that this increase is larger than the Black-White IQ gap. They then accused Murray of ignoring the importance of this Flynn effect with “some hand-waving about g…” This is a strange assertion because Herrnstein and Murray were the very scholars who labelled this secular increase in IQ scores “the Flynn effect,” after James Flynn, who did much to identify and publicize such gains. To understand fully why the Flynn effect is irrelevant to the Black-White IQ gap, we would have to discuss in detail something called the g factor, or general intelligence factor, because secular gains in IQ are inversely correlated with g loadings whereas the Black-White gap is positively correlated with g loadings. However, one doesn’t have to be a psychometrician to get the basic point.
Consider the following example: Men are taller than women (there is a height gap between men and women). Both men and women have increased in height since the 1700s. So, there is a secular increase in height (“Flynn effect” for height). But the gap between men and women in height has remained relatively stable (in the US, it has increased slightly in the past 100 years). The cause of the secular increase (probably nutrition) is different from the cause of the disparity between men and women (almost certainly genes); therefore, one (increase in height) has little to do with the other (gap between men and women). The same appears to be true for the Black-White IQ gap and the Flynn effect. The increase in IQ across the 20th century has little to do with the IQ disparity between Blacks and Whites.3
Large gains from adoption
Turkheimer et al argued that Murray is overly pessimistic about the ability to increase IQ in children, claiming that adoption “from a poor family into a better-off one is associated with gains of 12 to 18 points.” This claim stems from an analysis of six studies with 253 total subjects, and should be interpreted cautiously for several reasons. First, in one of the studies, the “poor families” from which the children were adopted were so poor that the children were suffering from primary undernutrition at the time of adoption. Second, most of the studies examined IQ at young ages, which is important because the genetic effect (heritability) of intelligence increases with age, a phenomenon labelled the “Wilson effect” by behavior geneticist Thomas Bouchard; therefore, the gains might be smaller if the subjects had been tested later in life. Third, even if one accepted the large IQ gains uncritically, those gains are still consistent with heritability estimates of 60%, as was clearly noted by Herrnstein and Murray in The Bell Curve (see page 771, note 86). And, fourth, as with the “Flynn effect” the adoption gains are primarily on subtests that are not strongly associated with g, which means that the cause(s) of the Black-White gap probably are different from the cause(s) of adoption IQ gains.
Heritability is lower in disadvantaged American children
Turkheimer et al contended that the heritability of intelligence is “markedly lower among American children raised in poverty” than among middle- or upper-class children. Although it is not immediately obvious, presumably Turkheimer et al believe this undermines the hereditarian position because more Black than White children are raised in poverty in the US. However, there are a number of problems with this argument.
First, many other studies that have examined the heritability of cognitive ability have found no or little evidence that heritability is lower in poor children. In a meta-analysis of available studies, Tucker-Drob and Bates found that there was no overall effect of socioeconomic status on the heritability of intelligence (in all studies, including ones from outside of the US), but that there was an effect in studies from the US. That effect, however, was small, and much smaller than in the original Turkheimer study that inspired this line of research. Second, the heritability of intelligence increases with age (the “Wilson effect”); therefore, even if the heritability of intelligence in some groups was low in childhood (say, 10% or so), it is not clear that it would remain low into adulthood.
Third, researchers recently found evidence that the heritability of intelligence is the same in Blacks and Whites. In fact, this was found in the same sample of youths (but also including non-twin siblings and half-siblings) that Turkheimer used for his original analysis.4 However, even if there is a small race difference in heritability, researchers could limit their analyses to middle- and upper-class Blacks and Whites, where the IQ gap is about the same, if not larger, than it is among lower-class Blacks and Whites. In other words, the fact that intelligence may be less heritable in impoverished youths is irrelevant to the debate about the cause(s) of race differences in intelligence.
What Turkheimer et al left out
To grapple honestly and dispassionately with the question of the etiology of the Black-White IQ gap requires confronting all the evidence. In their Vox article, Turkheimer et al accused hereditarians of being “mistaken theoretically” and “unfounded empirically” but they failed to forward even a partial list of the reasons many experts have come to believe hereditarianism is reasonable. Below, we will provide some of the important evidence they left out of their article. (See, also, the table for a more complete list).
Missing Puzzle Pieces
1] Hereditarians point to evolutionary histories and theory. Anatomically modern humans evolved in Africa roughly 200,000 years ago and eventually spread into Eurasia (and across the globe), settling in areas with diverse climates and environments. Around 10,000-15,000 years ago, some groups of humans became agriculturalists, which dramatically changed their interactions with their environments and food sources. Contrary to popular belief, 10,000 years is enough time for substantial and important evolutionary change in humans; and, in fact, copious evidence suggests that human population groups have diverged genetically and phenotypically from each other in the past 50,000 (and even 10,000) years because they evolved in different climates and socio-ecological niches.
Hereditarians hypothesize that population groups that evolved for 50,000 years in different environments developed not just superficial physical differences, but also cognitive differences. Prior scholars, for example, forwarded the “cold winters” theory of intelligence, which contends that cold, Northern Eurasian environments presented European and Asian ancestors with novel obstacles that might have selected for greater intelligence to navigate than environments closer to the equator. Arthur Jensen, in his definitive book on the g factor, noted, “It seems most plausible, therefore, that behavioral adaptations of a kind that could be described as complex mental abilities were more crucial for populations that migrated to Northern Eurasian regions…” (p. 436).5
2] Hereditarians point to a broader, global pattern of intelligence differences that is often ignored by environmentalists. Researchers have found that many different ethnic groups score differently on standardized IQ tests. Among the most consistent are that Sub-Saharan Africans score about 75; Blacks (African Americans) score about 85; Whites score about 100; East Asians score about 105; and Ashkenazi Jews score about 110. Of these scores, perhaps the most compelling for the hereditarian is the high intelligence of Ashkenazi Jewish people. It seems likely that when many first encounter the Black-White IQ gap, they think it environmental in origin because Blacks have faced horrific oppression and discrimination. The high Jewish IQ, however, immediately casts doubt on this intuition (as do copious data, which we have and will discuss) because Jewish people have also faced appalling discrimination throughout much of 18th, 19th, and 20th centuries (and well before, of course). If broad social biases and discrimination ineluctably suppressed IQ, then one would expect that Jewish people would score low on IQ tests and other indices of intelligence (such as intellectual achievement), especially in countries with histories of particularly virulent anti-Semitism. However, this is not the case, and even in countries with the ugliest legacies of anti-Semitism (e.g., Russia, Germany), Jewish people have been remarkably successful.
Hereditarians argue, therefore, that the global pattern of intelligence scores is difficult to understand from an environment-only perspective and requires the recognition of at least some genetic causation.
3] Hereditarians argue that the best transracial adoption study supports a priori hereditarian predictions. Although there are several studies in which the IQs of Blacks and Whites adopted into White families were measured, the best such study, the Minnesota Transracial Adoption Study (MTRAS), reported by Scarr and Weinberg in 1976 and by Weinberg, Scarr, and Waldman in 1992, found results congruent with hereditarianism. In 1975, when the adoptees were 7, those with two White biological parents scored 112; those with one White and one Black biological parent scored 109; and those with two Black biological parents scored 97. In a follow- up study in 1986, when the adoptees were 17, those with two White biological parents scored 106; those with one White and one Black biological parent scored 99; and those with two Black biological parents scored 89. Researchers have corrected the follow-up scores for the Flynn effect and attrition (some of the first sample was not tested the second time), finding the same IQ pattern (White-White parents highest; Black-White, second highest; Black-Black, lowest), but a different gap magnitude. However, even the magnitude of the gap of the most charitable “environment-only” analysis is nearly 12 IQ points. It is worth noting that there are other transracial adoption studies that report results less consistent with the hereditarian hypothesis, but those studies are generally lower quality than the MTRAS and/or only tested adoptees at early ages, when the heritability of IQ is fairly low.
4] Hereditarians argue that the high within-race heritability of intelligence (between 50% and 90%), coupled with a few corollary facts, makes it unlikely that the Black-White IQ gap is entirely environmental in origin. Critics of hereditarianism, including Turkheimer et al in their Vox article, have argued that the high within-race heritability of intelligence does not ipso facto mean that the Black-White IQ gap is itself genetic. Richard Lewontin and others made famous an example about corn seed that illustrates this point. To simplify, suppose that one bought corn seed and planted it in two different qualities of soil: one was nutritionally normal and one was nutritionally deficient. The subsequent corn crops in the normal soil averaged two feet in height; and the crops in the deficient soil averaged six inches. Suppose further that, because each soil was uniform in quality (normal or deficient), all of the height differences within each bed of soil were caused by genetics (100% heritability). One might be tempted to infer that the between corn plants’ difference in height was also caused by genes, but one would be wrong. The between-group height differences would be entirely environmental in origin.
Famous corn seed example of heritability
Although this example shows that it is possible that large group differences on highly heritable traits are entirely environmentally caused, it doesn’t show that the hereditarian argument is flawed. The example is artificial and requires positing two uniform environments with no overlap. It is difficult to argue that this situation is analogous to the Black-White IQ gap in the US, even if Blacks do face discrimination that (most) Whites do not.
A reasonable argument from high within-group heritability runs like this. The high heritability of IQ within-race means that environmental variance (within-race) has relatively little effect. As the philosopher of science Nevin Sesardic noted, the larger the heritability of IQ, the larger the environmental gap between Blacks and Whites would have to be to explain the Black-White gap environmentally. There is, as yet, no evidence that the Black-White environmental difference is large enough to explain the gap. To consider just one example, differences in socioeconomic status do not explain the gap. Whites are generally wealthier than Blacks in the US (median income $62,950 compared to $36,898), but controlling for income only shrinks the IQ gap by roughly 37%, and that is charitable to environmentalists, because IQ is causally related to income (not the other way around) and, therefore, controlling for income artificially shrinks the gap. (This would be similar to comparing differences in height between men and women but controlling for weight; being heavier does not cause you to be taller).
It is also worth noting that a similar plant example to that forwarded by environmentalists also shows that within-group heritabilities of 50% are consistent with an entirely genetic explanation of between-group differences. Of course, this does not mean that the Black-White IQ gap is entirely caused by genetics; rather, it simply means that the famous plant example, so long used as a cudgel against hereditarians, can be used, with slight alterations, to support an extreme version of hereditarianism.
Table: Partial list of evidence supporting hereditarianism
|Brain size differences||Best evidence suggests a small to moderate correlation between brain size and intelligence; there is a pattern of brain size differences that matches IQ scores. East Asians have larger brains than Caucasians, who have larger brains than African Americans.|
|Evolutionary based theory||Humans migrated out of Africa at least 50,000 years ago, settling in diverse environments. Those furthest from the equator likely confronted novel cognitive challenges. Populations likely evolved higher intelligence in response to these novel selection pressures. IQ scores correlate with distance from equator and with skin color (which indicates ancestral distance from equator).|
|Global pattern of IQ scores||Many ethnic groups score differently on IQ tests. Sub Saharan Africans = 75; African Americans = 85; Caucasians = 100; East Asians = 105; Ashkenazi Jews = 110.|
|High within-race heritability||Although not dispositive, the high within-race heritability of IQ (50%-90%) makes it plausible that at least some of the Black-White IQ gap is genetically caused. This is especially true because researchers have yet to find some unique environmental force that suppresses Black intelligence while not affecting White intelligence.|
|Pattern of life history traits||IQ patterns among races also match a suite of life history traits (traits associated with growth, survival, and reproduction).|
|Regression to the mean||Population traits tend to move toward the population (racial) mean from extreme cases. Two high-IQ people tend to have children with lower IQs. The opposite is also true. Two low-IQ people tend to have children with higher IQs. Multiple studies support hereditarian hypotheses. When children are matched at 120 IQ, Black siblings average about 100, whereas White siblings average about 110. When children are matched at 70 IQ, Black siblings average about 78, whereas White siblings average about 85.|
|Transracial adoption studies||Although adoption studies provide mixed evidence, the single best study, the Minnesota Transracial adoption study (MTRAS) clearly conforms with a priori hereditarian predictions. IQ W-W biological parents = 106; W-B biological parents 99; B-B biological parents = 89.|
|Psychometric patterns||Race differences are greatest on tests that are the most g loaded, which are also the most heritable. The Flynn effect manifests on tests that are less g loaded and less heritable. The Black-White gap on heavily g loaded tests has shrunk less than on more weakly g loaded tests.|
We have argued that Turkheimer et al’s Vox article is a misleading account of Murray’s (and the hereditarian) position and a one-sided review of the evidence. Turkheimer et al mischaracterize and overstate evidence that supports an environmentalist interpretation of the gap, while ignoring copious data that contradict it. To be sure, there is plenty of room for doubt about hereditarianism. We believe that, as of now, it is the best game in town. But we don’t think the cause of the Black-White IQ gap is a solved scientific puzzle. The only way to solve the puzzle is to grapple honestly and fairly with all of the evidence, which Turkheimer et al failed to do. Equally disappointingly, they made dubious moral claims, accusing those who advance the hereditarian position of ethically questionable behavior.
This is unfortunate for a couple of reasons. First, accusing honest scientists of immorality for pursuing a particular empirical question, for forwarding reasonable hypotheses, and for propounding those hypotheses publicly is unprofessional. Scientists owe allegiance to the evidence and to the truth, not to a particular moral or political perspective. Second, Vox is a widely read, liberal outlet that could have used this piece to challenge the prior assumptions of its readers. Instead, it published an ideologically saturated, liberally slanted piece that served merely to confirm their suspicions (“Murray really is peddling pseudoscience, so it’s okay to protest his campus talks”).
Of course, we understand that many people have legitimate concerns about studying race differences. It is true that bigoted people might use data about race and IQ to support nefarious political agendas, buttressing their own prejudices with scientific sounding arguments. However, the way to address this danger is not by distorting previous research or publicly attacking scholars who investigate this issue. Rather, it is by promoting the vision of society that Martin Luther King, Jr. advocated decades ago, one in which people are judged by their actions and the content of their characters and not by the average traits of a group (ethnic, political, religious, or otherwise).
The reality of racial variation cannot be hidden behind a veil of pleasant myths in perpetuity. And if researchers and moralists insist upon a noble lie about human genetic sameness, then they will not be prepared to grapple with the difficult ethical challenges that human variation in a cosmopolitan society presents.
Bo Winegard is a graduate student at Florida State University. Follow him on Twitter @EPoe187.
Ben Winegard is an Assistant Professor at Carroll College. Follow him on Twitter @BenWinegard.
Brian Boutwell is an Associate Professor of Criminology and Criminal Justice at Saint Louis University. Follow him on Twitter @fsnole1.
Todd Shackelford is a Distinguished Professor and Chair of Psychology at Oakland University, is the Editor of Evolutionary Psychology and is the Associate Editor of Personality and Individual Differences. Follow him on Twitter @TKShackelford.
1. Here are the show notes from the episode “Forbidden Knowledge”.
Interview starts with controversy over his book The Bell Curve [10:26]
Charles Murray requests that listeners read a few pages of his book to see that everything you’ve heard about it is wrong [13:18]
What is the thesis of The Bell Curve? [15:39]
The topic of intelligence is taboo even before you add race into it [18:16]
Has there been any new research on intelligence since you wrote The Bell Curve? [19:25]
The American Psychological Association established a task force the year after The Bell Curve was published to establish “knowns and unknowns” in the field of intelligence, and no claims in the book have been overturned since it was written [22:50]
Why didn’t you leave racial differences out of it? [27:07]
An explanation of standard deviation as it relates to IQ [28:40]
The validity and significance of IQ as a measure of intelligence [31:02]
Nothing to do with the results of the research if it’s genetically determined, but if they’re environmentally determined we can do something about it. [38:30]
Judith Rich Harris’s book – parents don’t have a very strong role in the outcomes of their children [41:40]
The fact that a trait is genetically transmitted doesn’t mean that differences between groups, when it comes to that trait, are also genetic in origin. A malnourished population could have “tall genes” but still have a shorter average height than a group without the “tall genes.” [42:45]
The Left used to be boosterish on IQ testing, IQ used to be seen as a direct road to meritocracy, and cut through class differences. A high SAT score can allow a child from a mediocre school to get into a good college and move up to a higher class [45:46]
Common knowledge vs elite knowledge – ordinary people accept IQ varies and matters, elites deny that IQ tests measure anything significant, but the scientific literature shows IQ matters [47:20]
Why we know IQ tests measure more than just the ability to take IQ tests—predictability of IQ tests has been established [49:35]
Murray addresses whether tests have cultural bias, uses example of SAT scores [50:45]
Discussion of the concept of race [54:09]
Genes are only part of the story, environment is also a factor [58:19]
Discussion of the Flynn Effect [1:01:45]
Ethical and political punchline—it would be irrational to judge any individual based on a knowledge of group differences. The variance between individuals within a group is much wider than the variance between the groups themselves [1:07:00]
Reaction and moral panic by academics/intellectuals—Murray didn’t see it coming [1:10:50]
Why talk about this subject at all, why seek data on racial/gender differences, what is the purpose? [1:13:04]
Were diversity promotion programs like affirmative action a mistake from the beginning? Are they a mistake now? [1:16:18]
The way Murray has been treated because of his work is an injustice, but that still doesn’t answer the question of why the research was worth doing in the first place – what are the motivations for doing this kind of research? How does it help society? [1:20:28]
Goal is to get to a truly color-blind society. Identity politics are a moral and political dead-end [1:25:50]
Discussion of the problem of social stratification [1:27:15]
“The hollow elite”—the new upper class doesn’t have a code of values that they hold others to; “they don’t preach what they practice” [1:34:50]
The extent of the isolation of coastal elites [1:40:25]
Effect of the narrow elite vs the broad elite [1:43:55]
What do you make of our current political situation? What’s your experience of being a conservative “never-trumper”? [1:47:00]
Discussion of universal basic income, and Murray’s endorsement of it [1:52:23]
Are you worried about the problem of the disincentive to work created by universal basic income? [1:58:07]
What are the similarities and differences between dysfunction in rural white America vs inner-city black America? [2:00:46]
What was your experience at Middlebury? [2:02:43]
Reiteration of why Murray is a guest on the podcast [2:05:00]
Murray says professors are the instigators of the protests [2:07:18]
Do you regret touching these topics and writing the book? [2:12:15]
2. Although there is no official consensus, it is clear that human populations vary genetically in ways generally concordant with self-identified racial identity.
3. This is the “hand waving” about g that Murray was referring to. It’s a very technical and subtle point that is important to understand the etiology of the Black-White IQ gap.
4. This result was confirmed in a personal communication by Turkheimer in 2013.
5. Cold winters theory is supported by some research of variable quality. For example, using fossilized skulls of Homo sapiens, Ash and Gallup demonstrated that cranial capacity was related to climatic variation and distance from the equator. Relatedly, Templer and Arikawa found a relation between winter temperature and IQ (colder = higher IQ) and Kanazawa found a relation between distance from the equator and IQ (further = higher IQ). Rindermann, Woodley, and Stratford found possible genetic support, discovering a link between genetic markers that evolved in cold environments and high intelligence. They concluded, “The presence of environmental harshness (i.e. extreme winter cold) suggests that factors relevant to the cold winters theory could have contributed to an increase in intelligence among the ancestors of those possessing these haplogroups [groups distinguished by genetic markers]” (p 370). We are hopeful that better methods, research, and debate will help clarify the evolutionary history of human intelligence.