Malcolm Gladwell writes in the New Yorker:
…The WISC [Wechsler Intelligence Scale for Children]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?”…
He goes on to show that the differences in IQ scores between blacks and whites reflects the lower level of cognitive stimulation black children often get, in large part because black children are more likely to grow up in single parent homes than white children, and because of urban inner city culture. The difference is not genetic, it is cultural, and it can be fixed – in part with better schools and with government social welfare programs that do not encourage out of wedlock births.
It's worth it to take the time to read the entire piece, especially because Commentary Magazine (disgracefully, I believe) spent a lot of energy promoting Charles Murray's and Richard Hernstein's The Bell Curve, and hasn't had the decency to retract despite the evidence proving those two men wrong.
If reading isn't your thing, you can hear a podcast interview with Gladwell by clicking here.