Books and Arts

Nature 423, 686-687 (12 June 2003) | doi:10.1038/423686a

Designer darwinism

Mark Ridley1

BOOK REVIEWEDDarwin and Design: Does Evolution Have a Purpose?

by Michael Ruse

Harvard University Press: 2003. 384 pp. $29.95, £19.95

Design — what biologists call 'adaptation' — is an obvious feature of life. People have probably been thinking about it for as long as they have been thinking about anything. Classically, it provided the basis of the 'argument from design', one of five arguments put forward for the existence of God. Darwin undermined that argument, but it has enjoyed something of a revival in the latest version of creationism, known as 'intelligent design creationism'.

Michael Ruse is a philosopher of biology, and his broad-ranging book covers several themes. He distinguishes the 'argument to complexity' — the factual observation that complex adaptations, such as eyes and wings, exist in nature — from the 'argument from design', the theological inference from that fact that God exists. Ruse traces the history of these two arguments from their earliest forms in the hands of Plato and Aristotle, through Galen and Thomas Aquinas, on to David Hume, Immanuel Kant and William Paley, followed by Georges Cuvier and Richard Owen, and then Darwin and his followers in the modern synthesis.

After the history, Ruse takes a look at modern research on adaptation, and at its 'formalist' critics, who think that organisms are shaped by non-adaptive laws of form, rather than by adaptation to the environment. He ends with two chapters on modern theologians, including the intelligent-design creationists.

There is no central argument to unify the book, but Ruse holds a consistently darwinian position against all its critics. Adaptation exists, he says; it matters; it is not explained by God; it is explained, and with exemplary scientific propriety, by natural selection; and it is a legitimate topic for scientific research. The various people who have argued otherwise are making various kinds of mistake.

The book is written for philosophers and theologians as well as scientists. Indeed, the book will help to broaden the minds of most scientific readers. I doubt whether anyone else has read up on quite the range of authors that Ruse has, and he writes about them clearly and non-technically.

Ruse also advances certain theses along the way that will particularly interest Nature readers, and I'll concentrate on them. One question concerns adaptationist research. The biologists who do this research often argue not only that they find adaptation interesting, but that it is peculiarly important in biology. Successful adaptationist research is explanatory in a way that makes most mechanistic research look descriptive. And any big theory about life has to be able to explain adaptation.

On this topic, Ruse gives a sympathetic hearing to the critics who, he says, "would raise the objection that adaptation and the associated design metaphor have their roots in British natural theology of the pre-Darwinian era, and they would ask again why, in the secular world of the twenty-first century, we should be bound by this retro-thinking." This seems to be close to confusing the contexts of discovery and of justification. Adaptationism may have its roots in predarwinian anglican theology, but that does not make it false. German textual scholarship may have its roots in lutheran theology, but that does not reduce the value of the texts.

I think the strongest argument that the critics can make is not that adaptation is unimportant, just one problem among many, but that it has been solved. This may level the playing field for adaptationist and non-adaptationist research now, but it does not reduce the conceptual importance of adaptation for understanding life.

Research into adaptation often uses optimality models, or something like them. It might aim to understand the form of an eye, for instance, on the assumption that eye shape is optimized for forming images. One common interpretation of this research is that it aims to understand how, and not whether, organisms are adapted. Ruse disagrees. "It is fairer to say that a two-way process is at work here. We adopt a background assumption of adaptationism and then we test specific models. Inasmuch as things do not work, then we worry more about our adaptationist background as well as our model."

I do not agree with Ruse on this point, but his position is undoubtedly defensible. The only place I had a deep disagreement was in the history of ideas, with what Ruse has to say about Motoo Kimura and the neutral theory of molecular evolution — the idea that most molecular evolution proceeds by random genetic drift. Kimura's ideas receive only a brief mention before being dismissed.

I favour the view that Kimura's idea led to something of a paradigm shift in the late 1980s. Most biologists who work on molecular evolution nowadays assume that they are mainly studying the effects of random drift. This contrasts with earlier biologists who worked with non-molecular characters. Kimura's ideas seriously challenged, or at least restricted the scope of, adaptationism. If adaptationism could carry on much as before, it was for reasons that needed further attention. So Kimura deserves more than a passing gesture in a survey as admirably thorough and sensible as Darwin and Design.

  1. Mark Ridley is in the Department of Zoology, Oxford University, Oxford OX1 3RS, UK.