What is Intelligence? Beyond the Flynn Effect
By James R. Flynn
Cambridge University Press £15.99 216 pages
FT bookshop price: £12.79

A more precise, if less exciting, title for this book might have been What is Intelligence Testing? since that is what it is mainly about. But don’t let that put you off. This is a mystery story – and an intriguing one.

In the early 1980s, the author, a US-born psychologist now living in New Zealand, made the startling discovery that, over the course of the 20th century and across the developed world, IQ test scores had shown big gains from one generation to the next. This phenomenon, which became known as “the Flynn effect”, had previously gone unnoticed because test scores were continually normalised to keep the mean at 100.

Picking up the story in this book, James Flynn notes that the phenomenon throws up several paradoxes. If people really are becoming more intelligent, why are we not struck by the extraordinary cleverness of our children or the stupidity of our parents? If, by present-day norms, the average IQ score in 1900 was between 50 and 70, are we to accept that most of our ancestors were, literally, mentally retarded?

And if, as has been shown over and again, genes dominate individual differences in IQ, how do we reconcile that with sudden leaps in IQ from parent to child? Why, as IQ scores rise, are people getting no better at arithmetic, vocabulary or general knowledge?

Yet it is this paradox that helps unravel the mystery. IQ tests are made up of sub-tests measuring a range of cognitive skills. People’s overall scores, it turns out, have shot up not because they are doing any better at basic skills they learn in the classroom, but because their scores have leapt in the tests measuring conceptual thinking and on-the-spot problem solving without learned rules.

Flynn attributes this to changes in society. Before 1900, most people had few years at school and then worked long hours doing repetitive jobs in factories, shops or agriculture. They had little opportunity or need for conceptual thinking, either at work or at leisure. Their minds were focused on practical matters, such as ownership, the useful, the beneficial and the harmful.

Now, we have mass secondary education and large numbers of people go into responsible jobs, where they are required to think for themselves. With more education comes a thirst for books and the arts and, since the 1950s, we have seen the emergence of a new visual culture. Our brain capacity has not grown, but we are using the capacity we have in more imaginative ways. A quick example: the market used to be a place in town where you went to buy and sell. Now it stands in people’s minds for a raft of concepts to do with the law of supply and demand.

The trouble is, all this takes barely a third of the book to say. Elsewhere, Flynn wanders off in various recondite directions, all the more infuriatingly because it leaves big questions unanswered: whether, for example, its core proposition could explain the differences in IQ scores between racial groups.

Thankfully, the book ends back on topic by wondering whether the gains in IQ scores, if a one-time adjustment to industrialisation, have come to an end in the developed world. If so, the developing world would have a chance to catch up – unless the developed countries leap ahead in wisdom and critical acumen, so far unmeasured.

Flynn thinks we should devise formal measures to quantify these skills. That would make IQ-testing seem like a doddle.

Richard Tomkins is the FT’s chief feature writer