Leaders of the American Psychological Association (APA), the foremost scientific society on psychology in the United States, determined that the debate was so pervasive and misinformed that “there was an urgent need for an authoritative report on these issues—one that all sides could use as a basis for discussion.”14 The APA Board of Scientific Affairs commissioned a task force chaired by Ulric Neisser of Emory University to prepare this report, which was published in 2006 with the title “Intelligence: Knowns and Unknowns” in the society's journal, American Psychologist.15 It was widely recognized among psychologists as an authoritative review of the state of scientific understanding regarding human intelligence at the time. A substantially updated review titled “Intelligence: New Findings and Theoretical Developments” was published in 2012, also in American Psychologist, by a group of seven experts in the field, headed by Richard Nisbett of the University of Michigan.16 These two reviews are among the most comprehensive summaries of the topic available.
Of the subjects treated in The Bell Curve, the most contentious was Herrnstein and Murray's conclusion that “the major ethnic groups in America differ, on the average, in cognitive ability,” and that a portion of these differences must be attributed to genetic differences between these groups.17 The argument in support of a hereditarian explanation for differences for intelligence among “major ethnic groups” can be distilled into a few principal points: First, most proponents of hereditarianism emphasize that the difference in average IQ scores between African Americans and European Americans is substantial. For example, a subheading in The Bell Curve is worded as a question: “How Large is the Black-White Difference?” The authors then respond:
The usual answer to this question is one standard deviation. In discussing IQ tests, for example, the black mean is commonly given as 85, the white mean as 100, and the standard deviation as 15.”18
To put this in perspective, IQ test results are normalized to an average of one hundred and a standard deviation of fifteen. The so-called “black mean” of eighty-five represents serious cognitive deficiencies in large numbers of people. Herrnstein and Murray were careful to point out that there is considerable variation in the different studies they compiled to derive this estimate. Even so, it is exactly the same estimate Jensen had arrived at twenty-five years earlier in his 1969 article. And, in recent years, several psychologists have pointed to data indicating that the gap has been narrowing, although others have marshaled different data to claim that it has not changed.19
Regarding Asian Americans and European Americans, Herrnstein and Murray note that the gap is much smaller: “In our judgment, the balance of the evidence supports the proposition that the overall east Asian mean is higher than the white mean. If we had to put a number on it, three IQ points currently most resembles a consensus, tentative though it still is.”20
The crux of their argument that these differences cannot be fully explained by environment, and therefore must be partly attributable to genetic differences between ethnic groups, is best stated in their own words:
Suppose that all the observed ethnic difference in tested intelligence originate in some mysterious environmental differences—mysterious, because we know from material already presented that socioeconomic factors cannot be much of the explanation. We further stipulate that one standard deviation (fifteen IQ points) separates American blacks and whites and that a fifth of a standard deviation (three IQ points) separates east Asians and whites. Finally, we assume that IQ is 60 percent heritable (a middle-ground estimate). Given those parameters, how different would the environments for the three groups have to be in order to explain the observed difference in these scores?
…The average environment of blacks would have to be at the 6th percentile of the distribution of environments among whites, and the average environment of East Asians would have to be at the 63rd percentile of environments among whites, for the racial differences to be entirely environmental.
Environmental differences of this magnitude and pattern are implausible…. An appeal to the effects of racism to explain ethnic differences also requires explaining why environments poisoned by discrimination and racism for some other groups—against the Chinese and the Jews in some regions of America, for example—have left them with higher scores than the national average.
…The heritability of individual differences in IQ does not necessarily mean that ethnic differences are also heritable. But those who think that ethnic differences are readily explained by environmental differences haven't been tough-minded enough about their own argument.21
After comparing arguments favoring a predominantly genetic explanation and a predominantly environmental explanation of the differences, they draw their final conclusion:
It seems highly likely to us that both genes and the environment have something to do with racial differences. What might the mix be? We are resolutely agnostic on that issue; as far as we can determine, the evidence does not yet justify an estimate.22
Though Herrnstein and Murray's book does not venture an estimate of how much genetic variation contributed to this difference, Rushton and Jensen's 2005 article does. They set up the controversy as a dichotomy of two contrasting models to explain average racial differences in IQ: a culture-only model, which they propose as 0 percent genetic and 100 percent environmental, and a hereditarian model, proposed as 50 percent genetic and 50 percent environmental. By the end of their article, they fully reject the culture-only model and recommended revision of their hereditarian model to 80 percent genetic and 20 percent environmental.23 They also speculate that a Darwinian approach explains their claim of a large hereditary difference between European, Asian, and African races for intelligence and other behavioral traits:
Evolutionary selection pressures were different in the hot savanna where Africans lived than in the cold northern regions Europeans experienced, or the even colder Arctic regions of East Asians. These ecological differences affected not only morphology but also behavior. It has been proposed that the farther north the populations migrated out of Africa, the more they encountered the cognitively demanding problems of gathering and storing food, gaining shelter, making clothes, and raising children successfully during prolonged winters. As these populations evolved into present-day Europeans and East Asians, the ecological pressures selected for larger brains, slower rates of maturation, and lower levels of testosterone—with concomitant reductions in sexual potency, aggressiveness, and impulsivity; increases in family stability, advanced planning, self-control, rule following, and longevity.24
These sorts of speculations—considered by many to be overtly racist and biased against African Americans—prompted a firestorm of responses. The scientific journal American Psychologist devoted an entire issue to the topic in 2005, titled Genes, Race, and Psychology in the Genome Era. The journal Psychology, Public Policy, and Law invited responses to Rushton and Jensen's article from prominent psychologists, responses that could hardly have been more polarized. For instance, educational psychologist Linda Gottfredson of the University of Delaware supported Rushton and Jensen's hereditarian view:
In summary, Rushton and Jensen (2005) have presented a compelling case that their 50%–50% hereditarian hypothesis is more plausible than the culture-only hypothesis. In fact, the evidence is so consistent and so quantitatively uniform that the truth may lie closer to 70%–80% genetic, which is the within-race heritability for adults in the West. The case for culture-only theory is so weak by comparison—so degenerated—that the burden of proof now shifts to its proponents to identify and replicate even one substantial, demonstrably nongenetic influence on the Black–White mean difference in g [general intelligence].25
Richard Nisbett of the University of Michigan drew a completely opposite conclusion in his review:
J. P. Rushton and A. R. Jensen (2005) ignore or misinterpret most of the evidence of greatest relevance to the question of heritability of the Black–White IQ gap. A dispassionate reading of the evide
nce on the association of IQ with degree of European ancestry for members of Black populations, convergence of Black and White IQ in recent years, alterability of Black IQ by intervention programs, and adoption studies lend no support to a hereditarian interpretation of the Black–White IQ gap. On the contrary, the evidence most relevant to the question indicates that the genetic contribution to the Black–White IQ gap is nil.26
Yale University professor of psychology Robert J. Sternberg (currently at Cornell University and former president of the American Psychological Association) condemned not only the scientific but also the public-policy views expressed in the article:
J. P. Rushton and A. R. Jensen (2005) purport to show public-policy implications arising from their analysis of alleged genetic bases for group mean difference in IQ…. None of these implications in fact follow from any of the data they present. The risk in work such as this is that public-policy implications may come to be ideologically driven rather than data driven, and to drive the research rather than be driven by the data.27
The core of the hereditarian controversy as it relates to differences between racial groups centers on three major issues: 1) how races are defined and categorized as supposedly distinct genetic entities, 2) how human intelligence is measured, and 3) how those measurements are interpreted in terms of genetic and environmental causes.
The first issue—the biological and social bases of racial classification—is one we've already discussed in detail in this book. The dispute focuses on the claim that racial categories represent genetically distinct groups as opposed to the idea that racial categorization is more of a social construct than a biological one. As Sternberg puts it:
Where does race fit into the genetic pattern we have been discussing above?…In fact, it does not fit at all. Race is a socially constructed concept, not a biological one. It is a result of people's desire to classify. People seem to be natural classifiers: they try to find order in the natural world…. Any set of observations of course can be categorized in multiple ways. People impose categorization and classification schemes that make sense to them and, in some cases, that favor their particular, often nonscientific, goals.28
Classification of people into a few racial categories (usually based on self-identification) grossly oversimplifies and obscures the genetic complexities of ancestry that underlie the realities of human diversity. Therefore, claims that IQ differences between races are largely genetic is scientifically flawed from the outset.
The second issue—measuring intelligence—has generated volumes of discussion, along with a variety of hypotheses to explain the meaning of metrics used to quantify intelligence. Much of the current psychological literature is focused on measuring IQ and an associated value called g, which is proposed as a numeric representation of general intelligence.29 Some have argued that g is a real and measurable aspect of human nature and that IQ tests reliably quantify it, particularly if components of IQ tests are weighted toward certain aspects of intelligence most relevant to g, a procedure called g-loading. Others counter that IQ and g are too narrow to encompass the complexities of human intelligence, and a one-dimensional measurement misrepresents true intelligence.
According to several reviews of the topic, there are three prominent theories. The first, often called CHC theory—after psychology professors Raymond Cattell, John Horn, and John Carroll—is a synthesis of several related theories. It posits g as a measure of general intelligence and proposes subdivision of g into g-f (fluid ability) and g-c (crystallized ability). Fluid ability is the capacity to think rapidly and deal successfully with new situations and previously unknown factors. Crystallized ability consists of the store of knowledge relevant to daily tasks that a person retains and can recall, such as vocabulary. Modern IQ testing and measurement of g are largely based on CHC theory, measuring aspects of both g-f and g-c, and such testing serves as the foundation for a large body of research on measuring intelligence.
An alternative is Gardner's theory of multiple intelligences, named after Harvard professor Howard Gardner. He disputes the validity of g as a general measure of intelligence and instead has proposed that intelligence falls into multiple categories: linguistic, mathematical, spatial, musical, bodily-kinesthetic, interpersonal, and intrapersonal. Although Gardner's theory of multiple intelligences has its proponents, a majority of psychologists have opted instead for the more simplistic CHC theory.
The third theory is the triarchic theory developed by Sternberg during the time he was a professor at Yale. It proposes three broad categories of intelligence: creative, analytical, and practical. He maintains that intelligence in each of these categories can be measured and that measurement of all three areas can “improve prediction of both academic and nonacademic performance in university settings and reduce ethnic-group differences.” Furthermore, he argues that this theory is important for education because “teaching that incorporates the various aspects of intelligence increases academic performance relative to conventional teaching.”30
Sternberg, along with Yale colleagues Elena Grigorenko and Kenneth Kidd, determines that “intelligence is, at this time, ill defined. Although many investigators study ‘IQ’ or ‘g’ as an operational definition of intelligence, these operationalizations are at best incomplete, even according to those who accept the constructs as useful.”31
Critics of intelligence tests also often question the validity of IQ tests because of culture bias. Certain cognitive skills may carry a higher value in one cultural tradition than in another, and tests—however well designed to avoid cultural bias—may still favor or disfavor people on the basis of their cultural background.
Nisbett and his colleagues, in their 2012 review of the current state of psychological research on human intelligence, sum up the situation as follows:
The measurement of intelligence is one of psychology's greatest achievements and one of its most controversial. Critics complain that no single test can capture the complexity of human intelligence, all measurement is imperfect, no single measure is completely free from cultural bias, and there is the potential for misuse of scores on tests of intelligence. There is some merit to all these criticisms. But we would counter that the measurement of intelligence—which has been done primarily by IQ tests—has utilitarian value because it is a reasonably good predictor of grades at school, performance at work, and many other aspects of success in life.32
They are quick to point out, however, that “types of intelligence other than the analytic kind examined by IQ tests certainly have a reality” and that “measuring nonanalytic aspects of intelligence could significantly improve the predictive power of intelligence tests.”33
In spite of the inability of IQ tests to fully represent the complexity of human intelligence, and largely for their predictive value regarding academic and employment success, IQ scores are widely used as the standard for much of the research on intelligence. However, because IQ scores do not fully represent human intelligence, Sternberg has cautioned that the language used in reference to intelligence is important: IQ represents a subset of cognition and should be referred to specifically as IQ, not as overall intelligence.34
We now move to the third issue at the core of the hereditarian controversy, which is perhaps the most contentious of the three. It is sometimes called the “nature versus nurture” debate, although a more accurate term is the heritability of intelligence. The term heritability means the proportion of overall variation in a population attributable to genetic variation. Body height, for instance, varies considerably among adults. Part of this variation is attributable to genetics (the combination of variants in DNA inherited by each person that influence body growth), and part is due to environmental variation (such as poor nutrition or diseases that may stunt growth during childhood). The heritability of body height in any population is simply a numerical value that defines what proportion of the overall variation for height is attributable to underlying genetic variation. It is often expressed as a perc
entage value between 0 and 100. A value of 80 percent heritability for body height in a particular population, for example, implies that 80 percent of the variation is attributable to genetic variation and 20 percent to nongenetic variation, presumably environmental variation.
Few scientists dispute that both genetic and environmental effects interact to influence variation for most characteristics, including human intelligence (in whatever way it is measured). What is disputed is whether differences between racially defined groups—such as the fifteen-point difference for average IQ scores between “American blacks and whites,” as stated by Herrnstein and Murray—is influenced by innate genetic differences between these groups.
As simple as it seems to be, heritability is unfortunately one of biology's most misunderstood and misapplied concepts. And most of this misunderstanding and misapplication boils down to three main points: First, heritability is a measure of variation, not magnitude. It tells us nothing about the degree of a trait, only what proportion of its variation can be attributed to genetic variation. Second, because it deals entirely with variation among individuals, it never applies to any single individual. Rather, it applies to each defined population in which it is measured. Third, heritability is not a permanently fixed value that can be measured in one population, then applied to another. It may vary among populations, and even over time in the same population, because environmental variation may change over time. Thus, strictly speaking, any measurement of heritability applies only to the population in which it is measured and at the time it is measured.
An often-used analogy, presented in various iterations by different authors, illustrates how heritability may be misapplied when attempting to explain racial-group differences in IQ. Perhaps the most cited version is by Harvard geneticist Richard Lewontin in a 1970 article titled “Race and Intelligence,”35 which was a critical response to Jensen's 1969 article “How Much Can We Boost IQ and School Achievement?” Lewontin asks us to imagine taking two handfuls of seeds from the same bag of genetically diverse seed corn, such that the genetic diversity of seeds in each handful is equivalent. One handful is planted and raised in a highly uniform environment with a fertilizer solution containing all the mineral nutrients the corn plants need for optimal growth (like the liquid fertilizers for houseplants sold in department and home improvement stores). The other is planted and grown in exactly the same environment but with a suboptimal fertilizer solution that has only half the nitrogen (a major nutrient needed by plants in relatively large amounts), and half the zinc (a minor nutrient needed in trace amounts). Over time, the corn plants grown in the environment with the optimal nutrient solution vary in height due solely to their genetic differences. The same is true for the plants grown with the solution that lacks optimal amounts of nitrogen and zinc. But the average height of plants grown in the optimal environment is greater than the average height of plants grown in the suboptimal environment because of the difference in nutrient supply. In both cases, heritability is 100 percent for each group because all variation within each group is due to genetic differences. The difference between the averages of the two environments, however, is entirely environmental because the genetic diversity of plants in the two environments is the same. Lewontin's point is that high heritability within a group provides no evidence whatsoever that differences between groups are genetic.
Everyone Is African Page 12
