Twins: And What They Tell Us About Who We Are (6 page)

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Authors: Lawrence Wright

Tags: #Family & Relationships, #Siblings, #Science, #Life Sciences, #Genetics & Genomics, #test

BOOK: Twins: And What They Tell Us About Who We Are
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the wide range of households into which the separated twins were adopted and found that there was no correlation at all between themand yet the IQs of the separated twins were still very similar. No other study had provided such comprehensive data on the relation of intelligence to social class and social mobility. It appeared to clinch the argument that intelligence is an inherited characteristic and that there is little that can be done in the way of tinkering with the environment to change that.
Three years after Burt's separated-twin study, Arthur R. Jensen, a psychologist at the University of California at Berkeley, published a magisterial attack on compensatory education in the
Harvard Educational Review
. "How Much Can We Boost IQ and Scholastic Achievement?" the title inquired. Jensen's essay, which shook the educational establishment and became the subject of discussion on talk shows and in the White House, was partly based on Burt's work, which was then still untarnished by the allegations of fraud that later covered his work with controversy. In his article, Jensen addressed the racial implications of the genetic transmission of intelligence, and the implications were gloomy indeed. Scores on standardized intelligence tests repeatedly demonstrated that the average black IQ lagged one standard deviation (15 IQ points) behind that of whites. Using the twin studies, which showed the heritability of intelligence to be about 0.80, Jensen argued that the effort to improve IQ among blacks by enriching the environment could produce, at best, a marginal gain, since environmental factors could account for only twenty percent of the difference. He concluded that we should abandon traditional methods of classroom instruction that begin with the premise that people are fundamentally alike in their
 
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mental capacities in favor of a model based on genetic diversity.
Of course, there is not a single gene for intelligencepresumably many different genes contribute to the trait that such standardized tests measurebut then, there is not a single gene for height, either. "The simple polygenic model for the inheritance of height fits the kinship correlations obtained for intelligence almost as precisely as it does for height," Jensen wrote. And yet, as several of his critics pointed out, the mean height in the United States and Japan has increased considerably in the last two centuries, too rapidly to be accounted for by genetic factors. Couldn't we expect the same of intelligence in an ideal learning environment?
Jensen conceded that there had been some general increase in height, but he proposed that it could be explained by the increased mobility among populations.
Outbreeding has increased at a steady rate ever since the introduction of the bicycle. For example, sons of parents who were from
different
Swiss villages were taller by approximately 1 inch than the sons of parents from the
same
village. The increase in heterozygosity, of course, eventually "saturates," and the effects level off, as has already occurred in the U.S. That genetic as well as nutritional factors are a major cause of the increase in actual height is further shown in the fact that approximately the same increase has occurred in all social classes in Western countries even though there have been nutritional differences among social classes.
Jensen concluded his argument: "Thus, the slight increase in the population's mean height over the last two centuriesthe environmentalists' favorite counter-argument to the high heritability of IQitself turns out to be largely a genetic phenomenon!"
 
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Obviously, if Jensen's premise were true, his solutiondividing students by lower and higher abilitieswould lead to schools that were resegregated along racial lines, this time because of supposed differences in student intelligence, rather than social discrimination. In fact, his argument was immediately enlisted by attorneys in a federal district court in a last-ditch effort to resist the desegregation of the Greensville and Caroline County, Virginia, public schools. The furor that resulted from the article was more personal than scholarly. For many years afterward, Jensen's mere appearance on a college campus would set off near riots.
In 1971, the psychologist Richard J. Herrnstein, confessing that he had been "submerged for twenty years in the depths of environmentalist behaviorism" as a former student of B. F. Skinner and a psychology professor at Harvard, wrote an equally provocative article simply titled "IQ" in the
Atlantic Monthly
. Herrnstein used much of the same material as Jensen (it became the basis for his book
IQ and the Meritocracy
and later
The Bell Curve
). The
New York Times
quoted him as saying that his "conclusions, if true, amounted to a death sentence for the ideal of egalitarianism.'' Buttressed by Burt's formidable data from twin studies, the hereditarian argument appeared to have climbed out of the Nazi grave to which it had been consigned.
Within a month after Herrnstein's article appeared, he was invited to speak at Princeton University on an unrelated subject ("The visual field of the pigeon"), but he declined to attend when the university could not make what he thought were sufficient guarantees for his safety. In place of his lecture there was a forum on academic freedom. Herrnstein was defended by Leon Kamin, a psychology professor who had known him at Harvard when both were students there. Kamin, how-
 
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ever, was a behaviorist who believed that there was no plausible evidence that intelligence was genetically transmitted. Because Herrnstein cited Burt's famous separated-twin study, Kamin decided to read it for himself. Within ten minutes of starting to read Burt, Kamin decided that "it was transparently clear that the guy was a fraud." He noticed, for instance, that Burt had published several studies of separated twins over the years, beginning with twenty-one pairs in 1955, increasing to "over 30" pairs in 1958, and concluding with the fifty-three pairs in 1966. Despite the fact that the sample size more than doubled over the years, the heritability of intelligence for identical twins reared apart remained exactly the same, even to the third decimal point, 0.771. For that matter, so did the heritability for the control group of twins reared together, 0.944. "The data were simply too perfect to be true," said Kamin. The unlikeliness of such astonishing consistencies was immediately apparent to anyone who had worked with statistics. Kamin also pointed out that Burt offered little information about how he collected the data or even such particulars as the age and sex of the children. "It was a fraud linked to policy from the word go,'' Kamin charged. "The data were cooked in order for him to arrive at the conclusions he wanted." It served to prove, Kamin asserted, that the IQ test itself was nothing more than "an instrument of oppression against the poor."
Kamin's investigation demolished Burt's scholarly reputation. Soon after that, a science reporter for the
Sunday Times
, Oliver Gillie, published a devastating exposé suggesting that two of Burt's associates, Misses Margaret Howard and J. Conway, who had coauthored papers with Burt and had done much of the actual testing of the twins, "never existed, but were the fantasy of
 
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an aging professor who became increasingly lonely and deaf." Burt was no longer alive to respond to these charges, and neither Howard nor Conway stepped forward to provide evidence of her reality. Jensen, who was a friend of Burt's, sought to defend the great man's honor, but when he tabulated the data from Burt's various studies, he came to the same conclusion as Kamin. In a 1974 article in
Behavior Genetics
, Jensen decreed that Burt's correlations were "useless for hypothesis testing"in effect, reading Burt out of the scientific literature. "It is almost as if Burt regarded the actual data as merely an incidental backdrop for the illustration of the theoretical issues in quantitative genetics, which, to him, seemed always to hold center stage," Jensen wrote. It was a gentler way of saying what Kamin had been charging, that the data were cooked to support Burt's political bias and class prejudice. The loss of Burt's data appeared to have a profound effect on the measure of the heritability of IQ. Christopher Jencks of Harvard recalculated the figures and found that without Burt's data, the correlation of heredity to IQ dropped from about eighty percent to sixty percent.
An authorized biography in 1979 by Leslie Hearnshaw, who had held the Chair of Psychology at Liverpool University until his retirement, largely agreed with Burt's detractors; for one thing, Hearnshaw wrote that only one twin has ever come forward to claim that he had been tested by Burt. That briefly seemed to settle the matter. However, Burt's reputation was at least partially resuscitated by two subsequent biographies, one in 1989 by the psychologist Robert B. Johnson of the University of Nottingham and the other in 1991 by the sociologist Ronald Fletcher of Reading University. The authors concluded that while Burt may have been a careless researcher, he was probably not the complete
 
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fraud that his detractors described. Moreover, they pointed out that the attack on Burt's reputation by critics holding opposing political views was itself full of careless, prejudicial reporting. Burt's raw data, which would settle much of the argument, had been partially destroyed by a bomb during the London blitz, and what remained of it was burned by his housekeeper after Burt's death, on the advice of one of Burt's bitterest opponents. On the other hand, Professor N. J. Mackintosh, who teaches experimental psychology at the University of Cambridge, re-examined Burt's twin data in 1995 and found substantial reasons to believe the charges of fraud. It is unlikely that this controversy will ever be satisfactorily resolved.
The bitterness of the battle over twin studies has rarely been matched in the history of academic warfare. The question of what twins tell us about human nature has been clouded by deeply held philosophical, political, and religious ideals. It is certainly true that the history of twin research is one of the most appalling chapters in science, having been born in Galton's aristocratic notions of the natural worthiness of the English upper class, taken to its evil extreme by Nazi eugenicists, and too readily used by American scientists to rationalize racial injustice. On the other hand, it is also true that the critics of twin studies have resorted to ad hominem attacks instead of persuasive scientific experiments. In many university libraries, basic twin research has been ransacked, articles have been ripped out of scientific journals, books have been stolen from the shelves. The 1970s especially were marked by a number of disgraceful episodes in which respectable scientists were harassed and besieged by radical students and by their own colleagues, who seemed to be more interested in stopping the research
 
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than in learning the truth. Lost, or at best ignored in the hubbub was the sacrifice of the twins themselves to the cause of science. In some exotic cases, the twins were not even aware of their sacrifice until some odd wind of destiny blew through their lives.

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