杏吧原创

DANIEL DENNETT has never been accused of modesty. His previous book, Consciousness Explained (鈥淚n Search of the Mind鈥檚 I鈥�, Review, 28 March 1992), was an ambitious assault on one of Western civilisation鈥檚 major, long-standing intellectual problems. A philosopher at Tufts University, Dennett advanced a novel perspective on the origin and mechanism of consciousness that, while not meeting the claim of the book (how could it?), demanded serious attention. Dennett鈥檚 new book Darwin鈥檚 Dangerous Idea is just as ambitious and worthy of great respect.

Dennett set himself an enormous task: that of explaining why everything of importance in the world of nature 鈥� from clams to trees, from birds to humans, including the human mind and its products 鈥� is the outcome of Darwinian evolution. On the way he seeks to demolish various claims of the Harvard evolutionist Stephen Jay Gould, the MIT linguist Noam Chomsky, and the Oxford mathematical physicist Roger Penrose, declaring that they are wrong, wrong, wrong in their views of evolution. Now that demands some immodesty. And, whether you conclude by the time you reach the end of this massive tome that Dennett makes his case or not, you have to admit that he is up to the challenge. Few mortals would be.

A separate question is whether many readers will be up to the challenge he sets as author, for this really is a weighty book. There鈥檚 no question that Dennett is a fine thinker and an accomplished writer, but for me he piled argument upon argument beyond what was necessary and intellectually digestible.

Dennett explains that he was propelled into writing the book by what he heard at a cognitive science symposium at the Massachusetts Institute of Technology in 1989. Among the topics being discussed was the nature of language. 鈥淭he level of hostility and ignorance about evolution that was unabashedly expressed by eminent cognitive scientists on that occasion shocked me,鈥� he recalls. The reason for the hostility, Dennett believes, is that 鈥淧eople ache to believe that we human beings are vastly different from all other species.鈥�

They are right, of course: Homo sapiens is the only species that has spoken language, highly developed consciousness, creativity and culture. But they are not right, Dennett argues, in assuming 鈥� in truth, yearning 鈥� that these attributes arose from mechanisms altogether different from the process that gave rise to birds鈥� wings and the elephant鈥檚 trunk 鈥� namely, evolution by natural selection. Opposition to or critiques of strict Darwinian theory stem from the desire to wrap all that we most cherish about ourselves in some kind of inexplicable mystery, says Dennett.

The triumph of Darwin鈥檚 theory was explaining how in the world of nature, an organism鈥檚 anatomy and behaviour appear to fit it so aptly for its environment. Before Darwin, scholars viewed this fit as the outcome of divine design, the work of God鈥檚 hand. After Darwin, it was recognised as the result of adaptation through natural selection. Minute change by minute change 鈥� over long periods of geological time 鈥� organisms are shaped to the exigencies of their environment. This is basic stuff, of course, at least for the 53 per cent of the American public that accepts evolutionary theory as a scientific explanation of life鈥檚 rich diversity. For Dennett, as for the Oxford biologist Richard Dawkins before him, it is everything.

And yet even for committed evolutionists there are questions and controversies to be bitterly fought over the strict interpretation of Darwinism. These have usually centred on the extent to which natural selection moulds life as we see it, and the rate at which evolutionary change occurs. Gould was among the most vocal in suggesting that other factors 鈥� such as historical contingency and architectural constraint 鈥� intervene in the possible outcome of evolution by natural selection. Those in the trade will remember the late 1970s and 1980s as a time of great debate over these issues.

Strict Darwinists viewed evolution, including the emergence of major novelties, as the outcome of gradual change. Gould (in company with biologist Niles Eldredge) argued that the pattern of history seen in the fossil record revealed a different story: brief periods of change interspersed with long periods of no change, or stasis. It was called punctuated equilibrium, or evolution by jerks, as one British wag put it. The pattern must say something about the process of evolution, Gould and Eldredge argued.

Dennett and Gould have replayed the most recent offensives in the battle in various arenas, including The New York Review of Books, and much of the central part of Darwin鈥檚 Dangerous Idea is a replay of that replay, in detail. Gould, according to Dennett, was very influential in creating a myth of revolution in thinking, but only a myth. Nothing changed, really, he argues, saying that Gould was simply 鈥渢he Boy who Cried Wolf鈥�. There was no fire, says Dennett. Strict Darwinism remains intact. 鈥淚t falls to me to dismantle the myth,鈥� says Dennett.

He is surely wrong here, because, again, those in the trade will remember the 1980s as a time when Darwinism was enriched by a wider perspective, one that included sentiments espoused by Darwin that had been swamped by early 20th-century enthusiasms of various kinds.

Nevertheless, Dennett鈥檚 arguments for why be believes he is right are well worth reading.

I sympathise with Dennett, however, in his perplexity over why Gould and Chomsky resolutely refuse to include human language within an evolutionary framework of natural selection. Gould has talked about the capacity for language arising as a secondary property of a brain that became large for other reasons. Chomsky鈥檚 claims are similar, though a little more mystical. But I question whether Dennett is correct in suggesting that Gould鈥檚 opinion reflects his 鈥渞eligious yearnings鈥�. The imputation fits the author鈥檚 thesis, that rejection of strict Darwinian theory within the human realm stems from an urge to see H. sapiens as special in the world of nature. But much of Gould鈥檚 writing rejects this view, too. There are many citations in the book that allow the reader to form a judgment.

When Dennett moves into ethics and morality in the final section of his book, he strays into an area in which the most vitriolic words have been exchanged 鈥� that of sociobiology. Again, these wars took place in the 1970s and 1980s. Are these cherished virtues of humanity the outcome of mindless Darwinian evolution? Or are they the mindful products of that unique feature of our species, culture?

All those years ago, sociobiology argued for the former 鈥� and Dennett backed it. And there has recently been a resurgence of such sentiments under a different guise, that of evolutionary psychology. Dennett is probably right here to support the notion that Darwinism reaches deep into the very soul of our species, and he rejects the suggestion that we are somehow diminished by the idea. How Dennett lucidly explains the interplay between genetics and Darwinism lucidly may be seen in the summary that ends the chapter on the topic: 鈥淓thical decision-making, examined from the perspective of Darwin鈥檚 dangerous idea, holds out scant hope of our ever discovering a formula or an algorithm for doing right. But that is not an occasion for despair; we have the mind-tools we need to design and redesign ourselves, ever searching for better solutions to the problems we create for ourselves and others.鈥� Each chapter ends this way followed by a brief summary of the next to come.

Even though life is not produced by a miracle, life鈥檚 products may still seem miraculous to us, and, in the glow of understanding provided by Darwinian theory, command our respect. 鈥淭he 鈥榤iracles鈥� of life and consciousness turn out to be even better than we imagined back when we were sure they were inexplicable,鈥� he concludes.

Why is Darwin鈥檚 idea 鈥渄angerous鈥�? Because, says Dennett, 鈥淚n a single stroke, the idea of evolution by natural selection unifies the realm of life, meaning, and purpose with the realm of space and time, cause and effect, mechanism and physical law.鈥� In other words, it cuts through every cherished notion we hold in life, from the simplest to the most complex, from the most abstract to the most personal. It is also, he admits, seductive, because it can explain everything, sometimes facilely so.

Dennett鈥檚 book is a bold work, which the reader may want tackle selectively rather than attempting to consume the whole at one sitting. That way you will come away from Darwin鈥檚 Dangerous Idea sated and stimulated, whether or not you agree with its thesis.