John R. Skoyles and Dorion Sagan

UP FROM DRAGONS

The evolution of human intelligence

In 1977 the late Carl Sagan wrote a book on the evolution of human intelligence called The Dragons Of Eden. A lot has been discovered about the brain since then and this book, one of whose authors is Carl's son, considers the subject afresh in the light of recent knowledge. It claims to be a sequel but also a fresh beginning.

The book seems to be aimed at readers with little prior knowledge of neuroscience and the style is "popular"; a bit too much so for my taste, in fact. I feel a little churlish in saying this, but I have to admit that I found the tone, which at times reminded me of a Readers' Digest article, faintly irritating—churlish, because there is actually a great deal of interesting and up-to-date information to be found. And the authors' statements are all fully referenced so that anyone interested can follow them up.

A wide range of territory is covered, including brain plasticity, memory and learning, and the neural basis of sociability. The unifying theme is brain in the context of evolution, and the later chapters consider how we may have reached our present situation and where we may go from here. Unlike some, Skoyles and Sagan are pretty optimistic about our prospects; they foresee us entering "a new era of humanity: the Brain Age".

One risk in writing a book of this kind is that, in attempting to be up-to-date, one may give undue prominence to speculations that later will turn out to be wrong or misleading. To be fair, the authors do signal this quite frequently, but even so I think unwary readers may not always realize how provisional much of our present understanding of the brain really is. The book also gives prominence to some questionable older theories, notably Paul MacLean's idea of the "triune brain". The notion of the brain as composed of "reptilian", "old mammalian", and "new mammalian" layers may be intuitively appealing but is open to serious objections (see, for example, Synaptic Self by Joseph Ledoux).

One of the most puzzling features of our evolutionary past is the question of why our brain enlarged so dramatically within a relatively short evolutionary time: about 2 million years. Skoyles and Sagan incline to the view that sexual selection was involved, but no definite conclusions emerge and the discussion slides off into a consideration of the role of long-distance running in our evolutionary past.

Chapter 12, entitled "What Are We?", is ostensibly about the notoriously intractable question of consciousness. One senses that the authors are not very happy at having to deal with this; in fact, they admit as much. "Indeed, we would rather not write this chapter and so enter the heated fray about this, the biggest question about the mind." The conclusion they reach is that much philosophizing on the subject in the past was misconceived and that all our ideas will have to change in the light of our increasing knowledge about the brain. "As little information as we have, it dwarfs the cumulative knowledge of previous centuries. Embarking on a quest to the gray continent of the brain without this knowledge is as foolhardy as trying to make sense of MRI scans of the body using Galen's theory of the four humors." For some, a robustly dismissive approach of this kind fails to do justice to the intrinsic difficulty of what David Chalmers calls the Hard Question.

Probably the best thing about this book is the large number of facts it cites; even readers who know a reasonable amount about neuroscience will probably gain some new information. And it succeeds in conveying a sense of its authors' enthusiasm for their subject; it would be a good choice to give to a young person who was thinking about embarking on a career in neuroscience. But it is not the kind of popular science writing that really appeals to me.

22 October 2003