If what I.Q. tests measure is immutable and innate, what explains the Flynn effect—the steady rise in scores across generations? Adrian Tomine

Correction appended.

One Saturday in November of 1984, James Flynn, a social scientist at the University of Otago, in New Zealand, received a large package in the mail. It was from a colleague in Utrecht, and it contained the results of I.Q. tests given to two generations of Dutch eighteen-year-olds. When Flynn looked through the data, he found something puzzling. The Dutch eighteen-year-olds from the nineteen-eighties scored better than those who took the same tests in the nineteen-fifties—and not just slightly better, much better.

Curious, Flynn sent out some letters. He collected intelligence-test results from Europe, from North America, from Asia, and from the developing world, until he had data for almost thirty countries. In every case, the story was pretty much the same. I.Q.s around the world appeared to be rising by 0.3 points per year, or three points per decade, for as far back as the tests had been administered. For some reason, human beings seemed to be getting smarter.

Flynn has been writing about the implications of his findings—now known as the Flynn effect—for almost twenty-five years. His books consist of a series of plainly stated statistical observations, in support of deceptively modest conclusions, and the evidence in support of his original observation is now so overwhelming that the Flynn effect has moved from theory to fact. What remains uncertain is how to make sense of the Flynn effect. If an American born in the nineteen-thirties has an I.Q. of 100, the Flynn effect says that his children will have I.Q.s of 108, and his grandchildren I.Q.s of close to 120—more than a standard deviation higher. If we work in the opposite direction, the typical teen-ager of today, with an I.Q. of 100, would have had grandparents with average I.Q.s of 82—seemingly below the threshold necessary to graduate from high school. And, if we go back even farther, the Flynn effect puts the average I.Q.s of the schoolchildren of 1900 at around 70, which is to suggest, bizarrely, that a century ago the United States was populated largely by people who today would be considered mentally retarded.

For almost as long as there have been I.Q. tests, there have been I.Q. fundamentalists. H. H. Goddard, in the early years of the past century, established the idea that intelligence could be measured along a single, linear scale. One of his particular contributions was to coin the word “moron.” “The people who are doing the drudgery are, as a rule, in their proper places,” he wrote. Goddard was followed by Lewis Terman, in the nineteen-twenties, who rounded up the California children with the highest I.Q.s, and confidently predicted that they would sit at the top of every profession. In 1969, the psychometrician Arthur Jensen argued that programs like Head Start, which tried to boost the academic performance of minority children, were doomed to failure, because I.Q. was so heavily genetic; and in 1994 Richard Herrnstein and Charles Murray, in “The Bell Curve,” notoriously proposed that Americans with the lowest I.Q.s be sequestered in a “high-tech” version of an Indian reservation, “while the rest of America tries to go about its business.” To the I.Q. fundamentalist, two things are beyond dispute: first, that I.Q. tests measure some hard and identifiable trait that predicts the quality of our thinking; and, second, that this trait is stable—that is, it is determined by our genes and largely impervious to environmental influences.

This is what James Watson, the co-discoverer of DNA, meant when he told an English newspaper recently that he was “inherently gloomy” about the prospects for Africa. From the perspective of an I.Q. fundamentalist, the fact that Africans score lower than Europeans on I.Q. tests suggests an ineradicable cognitive disability. In the controversy that followed, Watson was defended by the journalist William Saletan, in a three-part series for the online magazine Slate. Drawing heavily on the work of J. Philippe Rushton—a psychologist who specializes in comparing the circumference of what he calls the Negroid brain with the length of the Negroid penis—Saletan took the fundamentalist position to its logical conclusion. To erase the difference between blacks and whites, Saletan wrote, would probably require vigorous interbreeding between the races, or some kind of corrective genetic engineering aimed at upgrading African stock. “Economic and cultural theories have failed to explain most of the pattern,” Saletan declared, claiming to have been “soaking [his] head in each side’s computations and arguments.” One argument that Saletan never soaked his head in, however, was Flynn’s, because what Flynn discovered in his mailbox upsets the certainties upon which I.Q. fundamentalism rests. If whatever the thing is that I.Q. tests measure can jump so much in a generation, it can’t be all that immutable and it doesn’t look all that innate.

The very fact that average I.Q.s shift over time ought to create a “crisis of confidence,” Flynn writes in “What Is Intelligence?” (Cambridge; $22), his latest attempt to puzzle through the implications of his discovery. “How could such huge gains be intelligence gains? Either the children of today were far brighter than their parents or, at least in some circumstances, I.Q. tests were not good measures of intelligence.”

The best way to understand why I.Q.s rise, Flynn argues, is to look at one of the most widely used I.Q. tests, the so-called WISC (for Wechsler Intelligence Scale for Children). The WISC is composed of ten subtests, each of which measures a different aspect of I.Q. Flynn points out that scores in some of the categories—those measuring general knowledge, say, or vocabulary or the ability to do basic arithmetic—have risen only modestly over time. The big gains on the WISC are largely in the category known as “similarities,” where you get questions such as “In what way are ‘dogs’ and ‘rabbits’ alike?” Today, we tend to give what, for the purposes of I.Q. tests, is the right answer: dogs and rabbits are both mammals. A nineteenth-century American would have said that “you use dogs to hunt rabbits.”

“If the everyday world is your cognitive home, it is not natural to detach abstractions and logic and the hypothetical from their concrete referents,” Flynn writes. Our great-grandparents may have been perfectly intelligent. But they would have done poorly on I.Q. tests because they did not participate in the twentieth century’s great cognitive revolution, in which we learned to sort experience according to a new set of abstract categories. In Flynn’s phrase, we have now had to put on “scientific spectacles,” which enable us to make sense of the WISC questions about similarities. To say that Dutch I.Q. scores rose substantially between 1952 and 1982 was another way of saying that the Netherlands in 1982 was, in at least certain respects, much more cognitively demanding than the Netherlands in 1952. An I.Q., in other words, measures not so much how smart we are as how modern we are.

This is a critical distinction. When the children of Southern Italian immigrants were given I.Q. tests in the early part of the past century, for example, they recorded median scores in the high seventies and low eighties, a full standard deviation below their American and Western European counterparts. Southern Italians did as poorly on I.Q. tests as Hispanics and blacks did. As you can imagine, there was much concerned talk at the time about the genetic inferiority of Italian stock, of the inadvisability of letting so many second-class immigrants into the United States, and of the squalor that seemed endemic to Italian urban neighborhoods. Sound familiar? These days, when talk turns to the supposed genetic differences in the intelligence of certain races, Southern Italians have disappeared from the discussion. “Did their genes begin to mutate somewhere in the 1930s?” the psychologists Seymour Sarason and John Doris ask, in their account of the Italian experience. “Or is it possible that somewhere in the 1920s, if not earlier, the sociocultural history of Italo-Americans took a turn from the blacks and the Spanish Americans which permitted their assimilation into the general undifferentiated mass of Americans?”