Why so cross?

Thomas Nagel

  • Unweaving the Rainbow by Richard Dawkins
    Penguin, 350 pp, £20.00, October 1998, ISBN 0 07 139921 6
  • The Pattern of Evolution by Niles Eldredge
    Freeman, 225 pp, £17.95, February 1999, ISBN 0 7167 3046 4

Contemporary biologists who write for the general public usually have more to impart than scientific information. They have lessons to teach us about how to think of ourselves and our relation to the universe. This is not surprising, since biology is pervaded by Darwin’s theory of evolution, and the significance of that theory for our self-understanding remains largely unassimilated.

It isn’t just that evolution contradicts the Biblical story of the creation – which the Roman Catholic Church and most Protestant denominations don’t take literally any more. Darwin’s theory, as usually understood, is one of the most radically reductive scientific conceptions of all time, for it says that the appearance of purpose in the intricate design of living things and in their exquisite adaptation to their environments is an illusion: the whole plant and animal creation is a cosmic accident, or rather the result of a very long chain of accidents, explainable only in terms of the non-purposive laws of particle physics. That the process ever got started, with the formation of a suitable self-replicating molecule, seems to have depended on a chemical accident, though it is not possible at present to construct a realistic scenario that makes probable its occurrence in the time available since the earth began. And it seems radically contingent that, having begun, the process should have followed a path that included the appearance of vertebrates, mammals and ourselves. All this is obscured by the purposive-sounding Just-So stories by which evolution is often explained.

The writers of these two books have a string of popular works behind them. They also have a history of disagreement, with Dawkins on one side and Eldredge on the other. Eldredge is associated in this controversy with Stephen Jay Gould, his long-term research collaborator.[*] The disagreement, and the heat that it generates, are difficult for an outsider to understand, but they appear to have something to do with the way in which evolutionary theory is to be presented to a broader public. Dawkins is represented by Eldredge and Gould as a dogmatic, uncompromising ‘ultra-Darwinian’ reductionist who refuses to acknowledge the hierarchical complexity of the natural world, and Gould, if not Eldredge, is represented by Dawkins as a woolly romantic who inflates unremarkable data into profound mysteries.

The biological problem that is the focus of the dispute is set out most clearly in Eldredge’s book: what modification of the conception of the evolutionary process is required by the fact that the fossil record does not support Darwin’s belief that evolution proceeded gradually, and at a more or less constant rate? The fossil record is of course very patchy, but what it seems to reveal are species that come into existence, persist largely unchanged, often for millions of years, and then become extinct. It does not reveal long sequences of gradually changing ancestors of new species, linking them by minute intergenerational variation to predecessor species. Nor does it reveal the kind of gradual, cumulative intraspecies evolution that finally results in a difference great enough to constitute a new species.

Rather, the time required for the appearance of a new species is apparently very short by comparison with the time during which it then persists largely unchanged. A species that appears in the geological blink of an eye – say, ten thousand years, too short a time for any transitional stages to show up as fossils – may stay the same for five to ten million years after that. The process by which a new species is formed is apparently too fast to show up in the fossil record, but too slow to be observed in human experience. ‘No utterly convincing case of true speciation (that is, involving sexually reproducing organisms) has as yet emanated from a genetics lab,’ Eldredge writes.

He believes that these facts are incompatible with an unmodified version of Darwin’s theory, because Darwin believed in gradualism: that evolution proceeds at a constant rate, with gradual variations within species (of the kind commonly produced by animal breeders) leading to differences and branching that eventually become so great that they turn into separate species. In a sense, Eldredge says, Darwin didn’t believe in the reality of species, as discrete entities. What was real were individuals – and the gradually developing differences between them. Species, however, do seem in some sense real: their distinctness and internal uniformity both at a time and over time are striking. Eldredge and Gould coined the term ‘punctuated equilibria’ to describe their theory of this non-gradual evolutionary process whereby short bursts of rapid change are followed by long periods of stasis.

Now this might seem like the locus of a profound disagreement within evolutionary theory. What gives rise to new species, suddenly, if not the slow process of incremental change that Darwin envisioned? Does it mean that creative forces of some kind are at work, generating radically new forms of life through a process internal to the genetic material? That would certainly be incompatible with the reductionist outlook of the traditional theory of natural selection.

Eldredge thinks nothing of the kind, however. He is as committed to the mechanism of natural selection as Dawkins is. To account for speciation, he thinks it is necessary to bring in environmental and ecological factors: natural catastrophes that wipe out large numbers of species, like the dinosaurs, leaving room for others, like the mammals, to flourish; geological movements that separate subpopulations of a single species and, by preventing them from interbreeding, allow divergence through differential environmental selection; and so forth. In other words he argues, perfectly sensibly, that natural selection has to be understood as operating in interaction with facts about the surrounding world, and that stability is not surprising when the environment doesn’t change radically, or when populations can migrate to stay in an environment to which they are adapted. Even a temporary change, like a forest fire, will result only in a temporary upheaval of the population of life forms, followed by a gradual return to the earlier ecological equilibrium. Would any of those he calls ‘ultra-Darwinians’ deny this? Eldredge’s book opens by deriding Dawkins’s claim that it will eventually be possible to explain the structure of ecosystems in terms of the competition for replicative success among genes. But surely Dawkins doesn’t mean that this competition takes place in an environmental vacuum.

Dawkins’s book doesn’t attack Eldredge, but it expresses considerable irritation with Gould for making his antigradualism out to be more radical than it really is, and for encouraging others to think there are deep mysteries here that traditional Darwinian conceptions cannot penetrate. He seems to think Gould is selling out to those elements of the public who prefer mysteries to clear scientific explanations. It is hard to evaluate this charge, especially since Dawkins mainly supports it with quotations from others who have been influenced by Gould.

The charge, however, fits into the broader theme of Dawkins’s book, which is the threatening character many non-scientists find in reductive scientific explanations, and the consequent resistance to scientific understanding among humanists and other laymen. For a fellow scientist to play to this fear he finds unforgivable. Dawkins, by contrast, wants to present true, uncompromising science in lyrical terms, offering good poetic science as opposed to bad – and above all showing that scientific understanding can lift and expand the soul.

I find the enterprise a bit embarrassing, but can understand why he may have been goaded to it. As a dedicated and world-famous populariser of science he must be subject to constant assault from people who accuse him of cold-bloodedness, probably on the basis of his most famous title, The Selfish Gene. But he has a more distinguished target in the person of John Keats, who memorably said that Newton’s optical analysis of the rainbow destroyed its poetry. In answer to Keats and other poets distrustful of science, Dawkins says: ‘It is my thesis that the spirit of wonder which led Blake to Christian mysticism, Keats to Arcadian myth and Yeats to Fenians and fairies, is the very same spirit that moves great scientists; a spirit which, if fed back to poets in scientific guise, might inspire still greater poetry.’

Well, there may be a single, inchoate ‘spirit of wonder’ that expresses itself in the amazement everyone must feel at some point in life, over the tremendous fact of the existence of the universe and of himself. But I believe the yearning or questioning to which this wonder leads – and the type of response or answer which will come closest to satisfying it – is not the same from person to person, and that the differences reflect deep differences of temperament. Dawkins knows this, but tends to dismiss the demand for something besides science as if it were a preference for mysteries over answers. He quotes Blake –

To see a world in a grain of sand
And a heaven in a wild flower
Hold infinity in the palm of your hand
And eternity in an hour

– and says that he could write the same words with a very different meaning:

The stanza can be read as all about science, all about standing in the moving spotlight, about taming space and time, about the very large built from the quantum graininess of the very small, a lone flower as a miniature of evolution … The mystic is content to bask in the wonder and revel in a mystery that we were not ‘meant’ to understand. The scientist feels the same wonder but is restless, not content; recognises the mystery as profound, then adds, ‘But we’re working on it.’

One does not have to believe there is an incompatibility between poetry and science to find something absurd in this. The ‘mystic’ may think that there are some questions that remain unanswered, or some things that remain unsaid, even after all possible scientific knowledge has been assimilated, though he need not, like Keats, think that scientific information chills these other responses. Dawkins spends much of his book presenting the marvels of a reductive scientific image of the universe and its infinite variety, from light and sound and the Big Bang to speculations about the co-evolution of software and hardware – language and brain, perhaps – that led to the biological development of human intelligence. It’s just as thrilling as he thinks, without the help of his insistence that it is also ‘poetic’.

Poets can write about science, but science satisfies a very special hunger for understanding, the hope for universal order and reduction of complex variety to simple elements, so that the relations between things become intellectually transparent. This is not poetry – it is not like any art – and its effect on us does not require poetic forms of presentation, though it requires a gift for getting complex theoretical ideas across in ordinary language that few scientists have, but which Dawkins possesses to an exceptional degree.

Eldredge maintains that Dawkins and other ‘ultra-Darwinians’ are far too reductionist, wanting to explain everything in terms of natural selection and the competition of genes for survival. Gould recently published a long polemic about this in the New York Review of Books, but it is not easy to see the disagreement between the two schools as a large or significant one. Both sides believe that the influence of natural selection is enormous, but that it operates only in the context of environmental circumstances that make some characteristics of organisms adaptive and others not, and are responsible for the extinction of species from time to time. Both sides believe that some features are directly explained by natural selection, and others are mere side-effects. They also both acknowledge that physics and chemistry constrain and shape the biological possibilities and the range of possible genetic variation. So why are they so cross with each other?

My guess is that it is a conflict over purity. In the present state of understanding, the theory of evolution by genetic mutation and natural selection, through the differential reproductive success of individuals, is an explanatory schema. It describes the rough form of an interminable history of births, reproductions and deaths without specifying the enormously complex chemical details on which it depends, most of which will never be recovered. The actual story includes countless minute, non-lethal chemical changes in the DNA of reproductive cells each of which resulted, through embryonic development, in viable alternative organisms, slightly different from their parents.

This schema inevitably raises the question whether the story can be told entirely from the bottom up – everything being explained in terms of particle physics – or whether some higher-order principles of organisation enter the picture, increasing the story’s probability. This, I suspect, is what Dawkins thinks Gould and Eldredge are dangling before a public hungry for purpose, or some surrogate for it, in the natural world. And they, in return, think Dawkins is too quick to assure the public that a full reductionist explanation is available, when phenomena like the explosion in the number of species about 540 million years ago seem to defy such explanation.

The spectre of spontaneous generation haunts this subject. More than a century ago Pasteur refuted by experiment the hypothesis of spontaneous generation of bacteria, but the complexity of life is so extraordinary that the idea of higher-order material principles of self-organisation keeps making veiled appearances, as an alternative to reductionist confidence, which at present must rely on a good deal of hand-waving. Until the whole process from the initial origin of life through the evolutionary steps leading to the development of complex multicellular organisms is reduced to chemical first principles in a way consistent with the mathematical probabilities, with no arbitrary and unexplained principles of order or self-organisation, the strongly reductionist world picture will remain speculative. This, I suspect, is what lies behind the hostilities in evolutionary biology – the question of who, if anyone, is selling out, and who, if anyone, is claiming too much.

A beautiful little book by John Maynard Smith, Shaping Life: Genes, Embryos and Evolution (1998), part of a series entitled ‘Darwinism Today’, explains the present state of the reductionist project in the context of the astounding development from fertilised egg to adult organism, and observes that, oddly enough, there seems to be a correlation between holism (opposition to reductionism) and left-wing political sympathies. He says that in economics the correlation is reversed, because Adam Smith’s theory of the invisible hand, which underlies the ideology of the market, is holistic. I would say just the opposite: analysing social order as the interaction of countless self-interested individuals falls on the reductionist side of the fence. The terms are a bit slippery, but perhaps this shows that some forms of self-organisation are compatible with reductionism after all.

There is more in Dawkins and Eldredge than I have described. Eldredge gives a fascinating history of the interaction between geology and palaeontology, including the story of the discovery of plate tectonics and continental drift. I remember as a child thinking that the parallel between the east coast of the Americas and the west coast of Europe and Africa couldn’t be a coincidence, and that they must have drifted apart. Amazingly, it was only years later that this became scientifically intelligible, and the story of resistance to it, how it was overcome, and its relation to the interpretation of the fossil record, is quite wonderful. Dawkins discusses DNA fingerprinting, the unintuitive nature of probability, and various forms of unscientific nonsense, like astrology, that take in too many gullible people. There is a bit too much on the sociology and psychology of non-scientists’ attitudes to science rather than about science itself. But both books are rewarding, for the insatiable amateur.

[*] Gould’s latest book, Leonardo’s Mountain of Clams and the Diet of Worms (1998), doesn’t pursue the dispute. Gould is as usual a fine raconteur, on the subject of changes in the Catholic Church’s pronouncements on evolution, the doubtfulness of the adaptationist account of that paradigm of adaptation, the neck of the giraffe, Leonardo’s fossils and other topics.