BOOK REVIEW / Acid from the tree of life

A new study of Darwinian theory strenuously defends the great evolutionist. By Ray Monk; Darwin's Dangerous Idea: Evolution and the Meanings of Life By Daniel C Dennett Allen Lane, pounds 25

Imagine an acid so corrosive that it could eat through absolutely anything.What would you keep it in? Glass bottles and steel containers would be no more use than paper bags are to hold water. And, if you came across a dollop of this "universal acid", imagine what a trail of destruction it would leave in its wake. Such a substance would present an enormous problem: nothing would be safe from it. Perhaps in time, it might destroy the entire world.

Such is Daniel Dennett's central metaphor for Charles Darwin's "dangerous idea" of evolution by natural selection. "Bearing an unmistakable likeness to universal acid", he writes, Darwin's idea "eats through just about every traditional concept, and leaves in its wake a revolutionized world- view, with most of the old landmarks still recognizable, but transformed in fundamental ways".

Not that Dennett is appalled by this prospect; on the contrary, he celebrates it. For, unlike the fantasy of a universal acid, Darwin's dangerous idea is, he believes, demonstrably and unavoidably true. The danger it brings, then, is something we will just have to put up with, and what it destroys we will have to learn to live without. This includes not only the Biblical story of creation, but all idea of a personal God, all non-natural notions of aesthetic and ethical value, and even any conception of human minds, human consciousness or human agency that is incompatible with the assumption of natural selection as the fundamental explanation for the "tree of life" in all its variations.

It is a self-consciously hard-line view, and one Dennett defends with all the considerable rhetorical power (and even charm) at his disposal. He writes well and can turn a phrase better than most contemporary philosophers. Moreover, he explains the often difficult issues involved with a determination to be as clear as possible, which gives him a distinct advantage over his rivals. Against this, however, is the fact that the view he is advancing is one to which many people have a deep-seated revulsion. "Reductionism" is, to many, a dirty word, and the writers Dennett attacks - the zoologist Stephen Jay Gould, the physicist Roger Penrose, and the linguist Noam Chomsky - have found a large and receptive audience for their works precisely because they seem to offer, in one form or another, a non-reductionist view of the human mind, one that sees us as something more than the outcome of a set of blind, meaningless steps on the evolutionary path.

As Dennett realizes, he has his work cut out to convince us that nothing these - and other - writers have said makes any kind of dent in Darwinian orthodoxy. He felt compelled to make the attempt, however, because he found that his own work on the philosophy of mind - which marries Darwinian evolution to cognitive science to produce a thorough-going materialist version of Darwinianism - had, many felt, had been discredited. Irritated at being regarded as insufficiently up-to-date, Dennett decided to meet the challenge head-on and refute, one by one, the views that try to "contain" Darwin's idea in order to safeguard something - our minds, our language, life's rich variety, or whatever - from its corrosiveness. In this way, the book might be regarded as a massive footnote to his earlier Consciousness Explained, one designed to ward off this powerful source of objections to his materialist theory.

In other hands, this might have been a rather tiresome exercise in polemical axe-grinding, but through a lively style, the use of inventive metaphors and the odd personal revelation, Daniel Dennett, for the most part at least, keeps his readers engaged and potentially sympathetic to his cause.

As a piece of popular rhetoric, the book's chief flaw is that its driest and most difficult passages are near the beginning, where Dennett explains his conception of natural selection as a series of "algorithmic processes", mechanical, step-by-step procedures of the sort of which a computer programme is made. He probably lingers too long on this notion for most people's taste, and not long enough on the reflections of the "meanings of life" promised in the book's subtitle. "Is something sacred?" he concludes by asking. "Yes, say I with Nietzsche. I could not pray to it, but I can stand in affirmation of its magnificence. The world is sacred." Let's hope that Daniel Dennett will in time provide another massive footnote, explaining what he means by this remark.