How Intelligence Happens

This is an elegant book. The elegance begins with its appearance: slender, with sparing cover adornment in subdued colours, and no capital letters in the title or the author's name. It continues with the book's literary style, which is graceful without being flowery, engaging and easily comprehensible without being simplistic. And, most important, it extends to John Duncan's treatment of his topic.

The subject - intelligence and how it is manifested in the brain - is a fascinating one. Our brains, like those of all other species, consist of a very large but still finite number of individual, sometimes fungible and fragile cells that somehow make it possible for us to do everything from travelling to the Moon to building a microchip that can be inserted into a heart to keep it beating. We accomplish this through automatic responses to external and internal stimuli that take place in cells that are both extremely specific in their function at any one moment and extremely flexible in the functions to which they can be dedicated, in ways that leave us with the impression that we make our behavioural choices freely.

We pride ourselves on our ability to do so using rational processes, yet the machines we build using these rational processes can execute them much better than we can. At the same time, these machines cannot make the intuitive, often irrational leaps that give us some of our greatest insights and get us into some of our biggest pickles. Duncan recounts, almost in adventure story form, how psychologists, neuroscientists, computer scientists and neurologists have explored these processes over the past 100 years or so, and how they continue to do so.

As I said, this is an elegant book, and it is so partly because Duncan is a wise man. In his 30 years as a neuroscientist, he has been around the block a few times. He has seen many seemingly good explanations for patterns of brain function fall by the wayside because they are just too simple to account for all the data. The story he tells is engaging, as much for the wrong turns he describes as for the insights into the nature of intelligence he provides. But Duncan is wise and the book is elegant for another reason.

His subject is not just fascinating. It is also difficult. Although intelligence seems to be manifested in very similar ways within all human brains (and most non-human ones), there are large individual differences in the level at which humans manifest it. In other words, some people appear to have more of it than others. Unlike many in his area of research, Duncan doesn't shirk from addressing this issue. In an early chapter, he treats the history of this observation at length, and describes the large body of evidence that indicates that these individual differences in intelligence, whatever their source, have an impact on life outcomes ranging from health to wealth.

These individual differences form a backdrop to the rest of the book as he explores the brain functions of memory, attention, communication and coordination. But they remain a backdrop. Like the host of an elegant dinner in a mansion, Duncan keeps our focus on the guests and the furnishings. We are aware that people who are not guests and who live rather different lives from those of the guests are serving the courses and pouring the wine, but we do not look at them too closely, and we certainly don't ask them to explain themselves.