Unweaving the Rainbow: Science, Delusion and the Appetite for Wonder - Richard Dawkins (2000)


To gild refined gold, to paint the lily,
To throw a perfume on the violet,
To smooth the ice, or add another hue
Unto the rainbow, or with taper-light
To seek the beauteous eye of heaven to garnish,
Is wasteful and ridiculous excess.

King John, Act IV, scene ii

It is a central tenet of this book that science, at its best, should leave room for poetry. It should note helpful analogies and metaphors that stimulate the imagination, conjure in the mind images and allusions that go beyond the needs of straightforward understanding. But there's bad poetry as well as good, and bad poetic science can lead the imagination along false trails. That danger is the subject of this chapter. By bad poetic science I mean something other than incompetent or graceless writing. I am talking about almost the opposite: about the power of poetic imagery and metaphor to inspire bad science, even if it is good poetry, perhaps especially if it is good poetry, for that gives it the greater power to mislead.

Bad poetry, in the form of an over-indulgent eye for poetic allegory, or the inflation of casual and meaningless resemblances into huge cloudy symbols of a high romance (Keats's phrase), lurks behind many magical and religious customs. Sir James Frazer, in The Golden Bough (1922), recognizes a major category of magic which he calls homeopathic or imitative magic. The imitation varies from the literal to the symbolic. The Dyaks of Sarawak would eat the hands and knees of the slain in order to steady their own hands and strengthen their own knees. The bad poetic idea here is the notion that there is some essence of hand or essence of knee which can be transmitted from person to person. Frazer notes that, before the Spanish conquest, the Aztecs of Mexico

believed that by consecrating bread their priests could turn it into the very body of their god, so that all who thereupon partook of the consecrated bread entered into a mystic communion with the deity by receiving a portion of his divine substance into themselves. The doctrine of transubstantiation, or the magical conversion of bread into flesh, was also familiar to the Aryans of ancient India long before the spread and even the rise of Christianity.

Frazer later generalizes the theme:

It is now easy to understand why a savage should desire to partake of the flesh of an animal or man whom he regards as divine. By eating the body of the god he shares in the god's attributes and when he is a vine-god the juice of the grape is his blood; and so by eating the bread and drinking the wine the worshipper partakes of the real body and blood of his god Thus the drinking of wine in the rites of a vine-god like Dionysus is not an act of revelry, it is a solemn sacrament.

All over the world, ceremonies are based upon an obsession with things representing other things that they slightly resemble, or resemble in one respect. Powdered rhinoceros horn is, with tragic consequences, thought to be aphrodisiac, apparently for no better reason than the superficial resemblance of the horn itself to an erect penis. To take another common practice, professional rainmakers frequently imitate thunder or lightning, or they conjure a miniature 'homeopathic dose' of rain by sprinkling water from a bundle of twigs. Such rituals can become elaborate and costly in time and effort.

Among the Dieri of central Australia, rainmaking wizards, symbolically representative of ancestor gods, were bled (dripping blood represents the longed-for rain) into a large hole inside a hut especially built for the purpose. Two rocks, intended to stand for clouds and presage rain, were then carried by the two wizards some 10 or 15 miles away, where they were placed atop a tall tree, to symbolize the height of the clouds. Meanwhile, back at the hut, the men of the tribe would stoop low and, without using their hands, charge at the walls and butt their way through with their heads. They continued butting back and forth until the hut was destroyed. The piercing of the walls with their heads symbolized the piercing of the clouds and, they believed, released rain from real clouds. As an added precaution, the Great Council of the Dieri would also keep a stockpile of boys' foreskins in constant readiness, because of their homeopathic power to produce rain (do penises not 'rain' urine—surely eloquent evidence of their power?).

Another homeopathic theme is the 'scapegoat' (so-called because a particular Jewish version of the rite involved a goat), in which a victim is chosen to embody, signify, or be loaded up with, all the sins and misfortunes of the village. The scapegoat is then driven out, or in some cases killed, carrying the evils of the people with him. Among the Garos people of Assam, near the foothills of the eastern Himalayas, a langur monkey (or sometimes a bamboo rat) used to be captured, led to every house in the village to soak up their evil spirits and then crucified on a bamboo scaffold. In Frazer's words, the monkey

is the public scapegoat, which by its vicarious sufferings and death relieves the people from all sickness and mishap in the coming year.

In many cultures the scapegoat is a human victim, and often he is identified with a god. The symbolic notion of water 'washing' away sins is another common theme, sometimes combined with the idea of the scapegoat. In one New Zealand tribe,

a service was performed over an individual, by which all the sins of the tribe were supposed to be transferred to him, a fern stalk was previously tied to his person, with which he jumped into the river, and there unbinding, allowed it to float away to the sea, bearing their sins with it.

Frazer also reports that water was used by the rajah of Manipur as a vehicle to transfer his sins to a human scapegoat, who crouched under a scaffold on which the rajah took his bath, dripping water (and washed-away sins) on to the scapegoat below.

Condescension towards 'primitive' cultures is not admirable, so I have carefully chosen examples to remind us that theologies closer to home are not immune to homeopathic or imitative magic. The water of baptism 'washes' away sins. Jesus himself is a stand-in for humanity (in some versions via a symbolic standing in for Adam) in his crucifixion, which homeopathically atones for our sins. Whole schools of Mariology discern a symbolic virtue in the 'feminine principle'.

Sophisticated theologians who do not literally believe in the Virgin Birth, the Six Day Creation, the Miracles, the Transubstantiation or the Easter Resurrection are nevertheless fond of dreaming up what these events might symbolically mean. It is as if the double helix model of DNA were one day to be disproved and scientists, instead of accepting that they had simply got it wrong, sought desperately for a symbolic meaning so deep as to transcend mere factual refutation. 'Of course,' one can hear them saying, 'we don't literally believe factually in the double helix any more. That would indeed be crudely simplistic. It was a story that was right for its own time, but we've moved on. Today, the double helix has a new meaning for us. The compatibility of guanine with cytosine, the glove-like fit of adenine with thymine, and especially the intimate mutual twining of the left spiral around the right, all speak to us of loving, caring, nurturing relationships...' Well, I'd be surprised if it quite came to that, and not only because the double helix model is now very unlikely to be disproved. But in science, as in any other field, there really are dangers of becoming intoxicated by symbolism, by meaningless resemblances, and led farther and farther from the truth, rather than towards it. Steven Pinker reports that he is troubled by correspondents who have discovered that everything in the universe comes in threes:

the Father, the Son, and the Holy Ghost; protons, neutrons and electrons; masculine, feminine and neuter; Huey, Dewey, and Louie; and so on, for page after page.

How the Mind Works (1998)

Slightly more seriously, Sir Peter Medawar, the distinguished British zoologist and polymath whom I quoted before, invents a

great new universal principle of complementarity (not Bohr's) according to which there is an essential inner similarity in the relationships that hold between antigen and antibody, male and female, electropositive and electronegative, thesis and antithesis, and so on. These pairs have indeed a certain 'matching oppositeness' in common, but that is all they have in common. The similarity between them is not the taxonomic key to some other, deeper affinity, and our recognizing its existence marks the end, not the inauguration, of a train of thought.

Pluto's Republic (1982)

While I am quoting Medawar in the context of becoming intoxicated by symbolism, I cannot resist mentioning his devastating review of The Phenomenon of Man (1959), in which Teilhard de Chardin 'resorts to that tipsy, euphoristic prose poetry which is one of the more tiresome manifestations of the French spirit'. This book is, for Medawar (and for me now, although I confess that I was captivated when I read it as an over-romantic undergraduate), the quintessence of bad poetic science. One of the topics Teilhard covers is the evolution of consciousness, and Medawar quotes him as follows, again in Pluto's Republic:

By the end of the Tertiary era, the psychical temperature in the cellular world had been rising for more than 500 million years ... When the anthropoid, so to speak, had been brought 'mentally' to boiling-point some further calories were added ... No more was needed for the whole inner equilibrium to be upset ... By a tiny 'tangential' increase, the 'radial' was turned back on itself and so to speak took an infinite leap forward Outwardly, almost nothing in the organs had changed But in depth, a great revolution had taken place; consciousness was now leaping and boiling in a space of super-sensory relationships and representations...

Medawar drily comments:

The analogy, it should be explained, is with the vaporization of water when it is brought to boiling-point, and the image of hot vapour remains when all else is forgotten.

Medawar also calls attention to the notorious fondness of mystics for 'energy' and 'vibrations', technical terms misused to create the illusion of scientific content where there is no content of any kind. Astrologers, too, think that each planet exudes its own, qualitatively distinct 'energy', which affects human life and has affinities with some human emotion: love in the case of Venus, aggression for Mars, intelligence for Mercury. These planetary qualities are based on—what else?—the characters of the Roman gods after whom the planets are named. In a style reminiscent of the aboriginal rainmakers, the Zodiacal signs are further identified with the four alchemical 'elements': earth, air, fire and water. People born under earth signs like Taurus are, to quote an astrological page chosen at random from the worldwide web,

dependable, realistic, down to earth ... People with water in their chart are sympathetic, compassionate, nurturing, sensitive, psychic, mysterious and possess an intuitive awareness ... Those who lack water may be unsympathetic and cold.

Pisces is a water sign (I wonder why) and the element of water 'represents unconscious force's energy and power motivating us...'

Though Teilhard's book purports to be a work of science, his psychical 'temperature' and 'calories' seem approximately as meaningless as astrological planetary energies. The metaphorical usages are not usefully connected to their real-world equivalents. There is either no resemblance at all, or what resemblance there is impedes understanding rather than aids it.

With all this negativity, we mustn't forget that it is precisely the use of symbolic intuition to uncover genuine patterns of resemblance that leads scientists to their greatest contributions. Thomas Hobbes went too far when he concluded, in chapter 5 of Leviathan (1651), that

Reason is the pace; Encrease of Science, the way; and the Benefit of man-kind, the end. And, on the contrary, Metaphors, and senselesse and ambiguous words, are like ignes fatui; and reasoning upon them, is wandering amongst innumerable absurdities; and their end, contention, and sedition, or contempt.

Skill in wielding metaphors and symbols is one of the hallmarks of scientific genius.

The literary scholar, theologian and children's author C. S. Lewis, in a 1939 essay, made a distinction between magisterial poetry (in which scientists, say, use metaphoric and poetic language to explain to the rest of us something that we already understand) and pupillary poetry (in which scientists use poetic imagery to assist themselves in their own thinking). Important as both are, it is the second usage that I am emphasizing here. Michael Faraday's invention of magnetic 'lines of force', which we can think of as made of springy materials under tension, eager to release their energy (in the sense carefully defined by physicists) was vital to his own understanding of electromagnetism. I've already made use of the physicist's poetic image of inanimate entities—electrons, say, or light waves—striving to minimize their travel time. This is an easy way to get the right answer, and it is surprising how far it can be taken. I once heard Jacques Monod, the great French molecular biologist, say that he gained chemical insight by imagining how it would feel to be an electron at a particular molecular juncture. The German organic chemist Kekule reported that he dreamed of the benzene ring in the form of a snake devouring its tail. Einstein was forever imagining: his extraordinary mind led by poetic thought-experiments through seas of thought stranger than even Newton voyaged.

But this chapter is about bad poetic science and we come down with a bump in the following example, sent me by a correspondent:

I consider our cosmic environment has a tremendous influence on the course of evolution. How else do we account for the helical structure of DNA which may be either due to the helical path of incoming solar radiation or the path of Earth orbiting the Sun which, due to its magnetic axis, tilted at 23.5° from the perpendicular, is helical, hence the solstices and equinoxes?

Realistically, there is not the smallest connection between the helical structure of DNA and the helical path of radiation or the planet's orbit. The association is superficial and meaningless. None of the three assists our understanding of any of the others. The author is drunk on metaphor, captivated by the idea of the helix, which misleads him into seeing connections which do not illuminate the truth in any way. Calling it poetic science is too kind: it is more like theological science.

Recently my incoming mail has registered a sharp rise in the normal load of 'chaos theory', 'complexity theory', 'non-linear criticality' and similar phrases. Now I'm not saying that these correspondents lack the faintest, foggiest clue what they are talking about. But I will say it's hard to discover whether they do. New Age cults of all kinds cure swimming in bogus scientific language, regurgitated, half-understood (no, less than half) jargon: energy fields, vibration, chaos theory, catastrophe theory, quantum consciousness. Michael Shermer, in Why People Believe Weird Things (1997), quotes a typical example:

This planet has been slumbering for eons and with the inception of higher energy frequencies is about to awaken in terms of consciousness and spirituality. Masters of limitation and masters of divination use the same creative force to manifest their realities, however, one moves in a downward spiral and the latter moves in an upward spiral, each increasing the resonant vibration inherent in them.

Quantum uncertainty and chaos theory have had deplorable effects upon popular culture, much to the annoyance of genuine aficionados. Both are regularly exploited by those with a bent for abusing science and shanghaiing its wonder. They range from professional quacks to daffy New Agers. In America, the self-help 'healing' industry coins millions—and it has not been slow to cash in on quantum theory's formidable talent to bewilder. This has been documented by the American physicist Victor Stenger, author of the excellent Physics and Psychics (1990). One well-heeled healer wrote a string of bestselling books on what he calls 'quantum healing'. Another book in my possession has sections on quantum psychology, quantum responsibility, quantum morality, quantum aesthetics, quantum immortality and quantum theology. One feels vaguely let down that there is no 'quantum caring', but perhaps I missed it.

My next example packs a great deal of bad poetic science into a small space. It comes from the jacket blurb of a book:

A masterly description of the evolving, musical, nurturing and essentially caring universe.

Even if 'caring' were not a limp cliche, universes aren't the sort of entities to which a word like caring can sensibly be applied. (I realize that I am vulnerable to the criticism that a gene is not the sort of entity to which a word like 'selfish' should be applied. But I vigorously challenge anyone to maintain the criticism after reading The Selfish Gene itself, as opposed to just the title.) To apply 'evolving' to the universe is defensible but, as we shall see, it is probably best not to do so. 'Musical' is presumably an allusion to the Pythagorean 'music of the spheres', a piece of poetic science which may not have been bad originally but which we should have grown out of by now. 'Nurturing' has the smell of one of the most deplorable schools of bad poetic science, inspired by a misguided variant of feminism.

Here's another example. A number of scientists were invited by an anthologist in 1997 to send in the one question that they most wanted to see answered. Most of the questions were interesting and stimulating, but the following submission from one (male) individual is so absurd that I can only blame it on sucking up to feminist bullies:

What will happen when the male, scientific, hierarchical, control-oriented Western culture that has dominated Western thought integrates with the emerging female, spiritual, holographic, relationship-oriented Eastern way of seeing?

Did he mean 'holographic' or 'holistic'? Perhaps both. Who cares as long as it sounds good? Meaning is not what this is about.

The historian and philosopher of science Noretta Koertge, in her 1995 essay in Skeptical Inquirer, accurately puts her finger on the dangers of a kind of perverted feminism which could have a malign influence upon women's education:

Instead, of exhorting young women to prepare for a variety of technical subjects by studying science, logic, and mathematics, Women's Studies students are now being taught that logic is a tool of domination ... the standard norms and methods of scientific inquiry are sexist because they are incompatible with 'women's ways of knowing. ' The authors of the prize-winning book with this title report that the majority of the women they interviewed fell into the category of 'subjective knowers,' characterized by a 'passionate rejection of science and scientists.' These 'subjectivist' women see the methods of logic, analysis and abstraction as 'alien territory belonging to men' and 'value intuition as a safer and more fruitful approach to truth.'

One might have thought that, however dippy it might be, this kind of thinking would at least be gentle and, well, 'nurturing'. But the opposite is often true. At times it develops an ugly, hectoring tone, masculine in the worst sense. Barbara Ehrenreich and Janet Mcintosh, in their 1997 article on 'The New Creationism' in the Nation, recount how a social psychologist called Phoebe Ellsworth was intimidated at an interdisciplinary seminar on emotions. Though bending over backwards to pre-empt criticism, at one point she unguardedly mentioned the word 'experiment'. Immediately, 'the hands shot up. Audience members pointed out that the experimental method is the brainchild of white Victorian males.' Carrying conciliation to what would have seemed to me almost superhuman lengths, Ellsworth agreed that white males had done their share of damage in the world but noted that, none the less, their efforts had led to the discovery of DNA. This earned the incredulous (and incredible) retort: 'You believe in DNA?' Fortunately, there are still many intelligent young women prepared to enter a scientific career, and I should like to pay tribute to their courage, in the face of uncouth bullying of this kind.

Of course a form of feminist influence in science is admirable and overdue. No well-meaning person could oppose campaigns to improve the status of women in scientific careers. It is truly appalling (as well as desperately sad) that Rosalind Franklin, whose X-ray diffraction photographs of DNA crystals were crucial to Watson and Crick's success, was not allowed in the common room of her own institution and was therefore debarred from contributing to, and learning from, what might have been crucial scientific shop talk. It also may be true that women typically can bring a point of view to scientific discussions which men typically do not. But 'typically' is not the same thing as 'universally', and the scientific truths that men and women eventually discover (albeit there may be statistical differences in the kinds of research that they are drawn to) will be accepted equally by reasonable people of both sexes, once they have been clearly established by members of either sex. And no, reason and logic are not masculine instruments of oppression. To suggest that they are is an insult to women, as Steven Pinker has said:

Among the claims of 'difference feminists' are that women do not engage in abstract linear reasoning, that they do not treat ideas with skepticism or evaluate them through rigorous debate, that they do not argue from general moral principles, and other insults.

How the Mind Works (1998)

The most ridiculous example of feminist bad science may be Sandra Harding's description of Newton's Principia as a 'rape manual'. What strikes me about this judgement is less its presumption than its parochial American chauvinism. How dare she elevate her narrowly contemporary North American politics over the unchanging laws of the universe and one of the greatest thinkers of all time (who happened, incidentally, to be male and rather unpleasant)? Paul Gross and Norman Levitt discuss this and similar examples in their admirable book Higher Superstition (1994), leaving the last word to the philosopher Margarita Levin:

...much of feminist scholarly writing consists of wildly extravagant praise of other feminists. A's 'brilliant analysis' supplements B's 'revolutionary breakthrough' and C's 'courageous undertaking.' More disconcerting is the penchant of many feminists to praise themselves most fulsomely. Harding ends her book on the following self-congratulatory note: 'When we began theorizing our experience ... we knew our task would be a difficult though exciting one. But I doubt that in our wildest dreams we ever imagined we would have to reinvent both science and theorizing itself to make sense of women's social experience.' This megalomania would be disturbing in a Newton or Darwin: in the present context it is merely embarrassing.

In the rest of this chapter I shall deal with various examples of bad poetic science drawn from my own field of evolutionary theory. The first, which not all would regard as bad science and which can be defended, is the vision of Herbert Spencer, Julian Huxley and others (including Teilhard de Chardin) of a general law of progressive evolution working at all levels in nature, not just the biological level. Modern biologists use the word evolution to mean a rather carefully defined process of systematic shifts in gene frequencies in populations, together with the resulting changes in what animals and plants actually look like as the generations go by. Herbert Spencer, who, to be fair, was the first to use the word evolution in a technical sense, wanted to regard biological evolution as only a special case. Evolution, for him, was a much more general process, with shared laws at all its levels. Other manifestations of the same general law of evolution were the development of the individual (the progression from fertilized egg through foetus to adult); the development of the cosmos, the stars and the planets from simpler beginnings; and progressive changes, over historical time, in social phenomena such as the arts, technology and language.

There are good things and bad about the poetry of general evolutionism. On balance I think it fosters confusion more than illumination, but there is certainly some of both. The analogy between embryonic development and species evolution was artfully exploited by that irascible genius J. B. S. Haldane to make a debating point. When a sceptic of evolution doubted that anything so complicated as a human could have come from single-celled beginnings, Haldane promptly observed that the sceptic himself had done that very thing and the whole process took only nine months. Haldane's rhetorical point is undiminished by the fact, which of course he knew perfectly well, that development is not the same thing as evolution. Development is change in the form of a single object, as clay deforms under a potter's hands. Evolution, as seen in fossils taken from successive strata, is more like a sequence of frames in a cinema film. One frame doesn't literally change into the next, but we experience an illusion of change if we project the frames in succession. With this distinction in place, we can quickly see that the cosmos does not evolve (it develops) but technology does evolve (early aeroplanes are not moulded into later ones but the history of aeroplanes, and of many other pieces of technology, falls well into the cinema frame analogy). Clothes fashions, too, evolve rather than develop. It is controversial whether the analogy between genetic evolution, on the one hand, and cultural or technical evolution, on the other, leads to illumination or the reverse, and I am not going to get into that argument now.

My remaining examples of bad poetry in evolutionary science come largely from a single author, the American paleontologist and essayist Stephen Jay Gould. I am anxious that such critical concentration upon one individual shall not be taken as personally rancorous. On the contrary, it is Gould's excellence as a writer that makes his errors, when they occur, so eminently worth rebutting.

In 1977 Gould wrote a chapter on 'eternal metaphors of paleontology' to introduce a multi-authored book on the evolutionary study of fossils. Beginning with Whitehead's preposterous, though much quoted, statement that all of philosophy is a footnote to Plato, Gould's thesis, in the words of the preacher of Ecclesiastes (whom he also quotes), is that there is nothing new under the sun: 'The thing that hath been, it is that which shall be; and that which is done is that which shall be done.' Current controversies in paleontology are just old controversies being recycled. They

preceded evolutionary thought and found no resolution within the Darwinian paradigm ... Basic ideas, like idealized geometric figures, are few in number. They are eternally available for consumption...

Gould's eternally unresolved questions in paleontology are three in number: Does time have a directional arrow? Is the driving motor of evolution internal or external? Does evolution proceed gradually or in sudden jumps? Historically, he finds examples of paleontologists who have espoused all eight possible combinations of answers to these three questions, and he satisfies himself that they straddle the Darwinian revolution as though it never happened. But he manages this feat only by forcing analogies between schools of thought which, carefully examined, have no more in common than blood and wine, or helical orbits and helical DNA. All three of Gould's eternal metaphors are bad poetry, forced analogies that obscure rather than illuminate. And bad poetry in his hands is all the more damaging because Gould is a graceful writer.

The question whether evolution has a directional arrow is certainly one that can sensibly be asked, in various guises. But the bedfellows that the different guises bring together are so ill matched that they are not usefully united. Does bodily structure get progressively more complex as evolution goes on? This is a reasonable question. So is the question of whether the total diversity of species on the planet increases progressively as the ages go by. But they are utterly different questions and it is conspicuously unhelpful to invent a century-spanning school of 'progressivist' thought to unite them. Still less do either of them, in their modern form, have anything in common with the pre-Darwinian schools of 'vitalism' and 'finalism', which held that living things were progressively 'driven' from within, by some mystical life force, towards an equally mystical final goal. Gould forces unnatural connections among all these forms of progressivism, as a device to support his poetic historical thesis.

Much the same is true of the second eternal metaphor, and the question of whether the motor of change is in the external environment, or whether change arises from 'some independent and internal dynamic within organisms themselves'. A prominent modern disagreement is between those who believe that the main driving force of evolution is Darwinian natural selection and those who emphasize other forces such as random genetic drift. This important distinction is not conveyed, not even to the smallest extent, by the internalist/externalist dichotomy that Gould would force upon us in order to maintain his thesis that post-Darwinian argumentation is just a recycling of pre-Darwinian equivalents. Is natural selection externalist or internalist? It depends whether you are talking about adaptation to the external environment or co-adaptation of the parts to each other. I shall return to this distinction later in another context.

Bad poetry is even more evident in Gould's exposition of the third of his eternal metaphors, the one concerning gradual versus episodic evolution. Gould uses the word episodic to unite three kinds of sharp discontinuity in evolution. These are: first, catastrophes such as the mass extinction of the dinosaurs; second, macromutations or saltations; and third, punctuation in the sense of the theory of punctuated equilibrium proposed by Gould and his colleague Niles Eldredge in 1972. This last theory needs more explanation, and I'll come to it in a moment.

Catastrophic extinctions are straightforward to define. Exactly what causes them is controversial and probably different in different cases. For the moment, just notice that a worldwide catastrophe in which most species die is, to put it mildly, not the same thing as a macromutation. Mutations are random errors in gene copying and macromutations are mutations of large effect. A mutation of small effect, or micromutation, is a small error in gene copying, whose effect on its possessors might be too slight to notice easily, say a subtle lengthening of a leg bone, or a hint of reddening in a feather. A macromutation is a dramatic error, a change so large that, in extreme cases, its possessor would be classified in a different species from its parents. In my previous book, Climbing Mount Improbable, I reproduced a photograph from a newspaper of a toad with eyes in the roof of its mouth. If this photograph is genuine (a big if, in these days of Photoshop and other handy image-manipulation software), and if the error is genetic, the toad is a macromutant. If such a macromutant spawned a new species of toads with eyes in the roofs of their mouths, we should describe the abrupt evolutionary origin of the new species as a saltation or evolutionary jump. There have been biologists, such as the German/American geneticist Richard Goldschmidt, who believed that such saltatory steps were important in natural evolution. I am one of many who have cast doubt on the general idea, but that is not my purpose here. Here I make the much more basic point that such genetic leaps, even if they occur, have nothing in common with earth-shattering catastrophes such as the sudden extinction of the dinosaurs, except that both are sudden. The analogy is purely poetic, and it is bad poetry which doesn't lead to any further illumination. Recalling Medawar's words, the analogy marks the end, not the inauguration, of a train of thought. The ways of being a non-gradualist are so varied as to strip the category of all usefulness.

The same applies to the third category of non-gradualists: punctuationists in the sense of Eldredge and Gould's theory. The idea here is that a species comes into existence in a time which is short compared with the much longer period of 'stasis' during which it survives unchanged after its initial formation. In the extreme version of the theory, the species, once it has burst into existence, continues unchanged until either it goes extinct or it splits to form a new daughter species. It is when we ask what happens during the sudden bursts of species formation that the confusion, born of bad poetry, arises. There are two things that might happen. They are utterly different from each other, but Gould makes light of the difference because he is seduced by bad poetry. One is macromutation. The new species is founded by a freak individual, like the alleged toad with eyes in the roof of its mouth. The other thing that might happen—more plausibly, in my view, but I'm not talking about that now—is what we can call rapid gradualism. The new species comes into existence in a brief episode of rapid evolutionary change which, although gradual in the sense that parents don't spawn an instant new species in a single generation, is fast enough to look like an instant in the fossil record. The change is spread over many generations of small, step-by-step increments, but it looks like a sudden jump. This is either because the intermediates lived in a different place (say, on an outlying island) and/or because the intermediate stages passed too rapidly to fossilize—10,000 years is too short to measure in many geological strata, yet it constitutes ample time for quite major evolutionary change to accumulate gradually in small steps.

There is all the difference in the world between rapid gradualism and macromutational saltation. They depend upon totally different mechanisms and they have radically different implications for Darwinian controversies. To lump them together simply because, like catastrophic extinctions, they all lead to discontinuities in the fossil record, is bad poetic science. Gould is aware of the difference between rapid gradualism and macromutation, but he treats the matter as though it were a minor detail, to be cleared up after we have taken on board the overarching question of whether evolution is episodic rather than gradual. One can see it as overarching only if one is intoxicated by bad poetry. It makes as little sense as my correspondent's question about the DNA double helix and whether it 'comes from' the earth's orbit. Once again, rapid gradualism no more resembles macromutation than a bleeding wizard resembles a shower of rain.

Even worse is to claim catastrophism under the same punctuationist umbrella. In pre-Darwinian times the existence of fossils became increasingly embarrassing for upholders of biblical creation. Some hoped to drown the problem in Noah's flood, but why did the strata seem to show dramatic replacements of whole faunas, each one different from its predecessor, and all of them largely free of our own, familiar creatures? The answer given by, among others, the nineteenth-century French anatomist Baron Cuvier, was catastrophism. Noah's flood was only the last in a series of cleansing disasters visited upon the earth by a supernatural power. Each catastrophe was followed by a new creation.

Apart from the supernatural intervention, this has something—a little—in common with our modern belief that mass extinctions such as those that ended the Permian and Cretaceous eras were followed by new flowerings of evolutionary diversity to match previous radiations. But to lump the catastrophists in with macro-mutationists and with modern punctuationists, just because all three can be represented as non-gradualist, is very bad poetry indeed.

After giving lectures in the United States, I have often been puzzled by a certain pattern of questioning from the audience. The questioner calls my attention to the phenomenon of mass extinction, say, the catastrophic end of the dinosaurs and their succession by the mammals. This interests me greatly and I warm to what promises to be a stimulating question. Then I realize that the tone of the question is unmistakably challenging. It is almost as though the questioner expects me to be surprised, or discomfited, by the fact that evolution is periodically interrupted by catastrophic mass extinctions. I was baffled by this until the truth suddenly hit me. Of course! The questioner, like many people in North America, has learned his evolution from Gould, and I have been billed as one of those 'ultra-Darwinian' gradualists\ Doesn't the comet that killed the dinosaurs also blow my gradualistic view of evolution out of the water? No, of course it doesn't. There is not the smallest connection. I am a gradualist in the sense that I don't think macromutations have played an important role in evolution. More determinedly, I am a gradualist when it comes to explaining the evolution of complex adaptations like eyes (so is any sane person, including Gould). But what on earth have such matters got to do with mass extinctions? Nothing at all. Unless, that is, your mind has been filled up with bad poetry. For the record, I believe, and have believed for the whole of my career, that mass extinctions exert a profound and dramatic influence on the subsequent course of evolutionary history. How could they not? But mass extinctions are not a part of the Darwinian process, except in so far as they clear the decks for new Darwinian beginnings.

There is irony lurking here. Among the facts about extinction that Gould is fond of emphasizing is its capriciousness. He calls it contingency. When mass extinction strikes, major groups of animals die wholesale. In the Cretaceous extinction, the once mighty group of dinosaurs (with the notable exception of birds) was completely wiped out. The choice of major group for victim is either random or, if non-random, it is not the same non-randomness as we see in conventional natural selection. The normal adaptations to survival do not avail against comets. Grotesquely, this fact is sometimes trotted out as if it were a debating point against neo-Darwinism. But neo-Darwinian natural selection is selection within species, not between species. To be sure, natural selection involves death, and mass extinction involves death, but any further resemblance between the two is purely poetic. Ironically, Gould is one of the few Darwinians who still think of natural selection as working at levels higher than the individual organism. It would never occur to the rest of us even to ask whether mass extinctions are selective events. We might see extinction as opening up new opportunities for adaptation, by lower-level natural selection choosing between individuals separately within each species that has survived the catastrophe. As a further irony, it is the poet Auden who came nearer to getting it right:

But catastrophes only encouraged experiment As a rule, it was the fittest who perished, the mis-fits, forced by failure to emigrate to unsettled niches, who altered their structure and prospered.

'Unpredictable but Providential (for Loren Eiseley)'

I take one further extended example of bad poetic science from paleontology, and once again Stephen Jay Gould is responsible for its popularity even if he has not clearly expressed it himself in its extreme form. Many readers of his elegantly written book Wonderful Life (1989) have been captivated by the idea that there was something special and unique about the whole business of evolution in the Cambrian era, when fossils of most of the great animal groups first appeared, rather over 500 million years ago. It is not just that the animals of the Cambrian were peculiar. Of course they were. The animals of every era have their peculiarities and the Cambrian ones were arguably more peculiar than most. No, the suggestion is that the whole process of evolution in the Cambrian was odd.

The standard neo-Darwinian view of the evolution of diversity is that a species splits into two when two populations become sufficiently unalike that they can no longer interbreed. Often the populations begin diverging when they chance to be geographically separated. The separation means that they no longer mix their genes sexually and this permits them to evolve in different directions. The divergent evolution might be driven by natural selection (which is likely to push in different directions because of different conditions in the two geographical areas). Or it might consist of random evolutionary drift (since the two populations are not genetically held together by sexual mixing, there is nothing to stop them drifting apart). In either case, when they have evolved sufficiently far apart that they could no longer interbreed even if they were geographically united again, they are defined as belonging to separate species.

Subsequently, the lack of interbreeding permits further evolutionary divergence. What had been distinct species within one genus become, in the fullness of time, distinct genera within one family. Later, families will be found to have diverged to the point where taxonomists (specialists in classification) prefer to call them orders, then classes, then phyla. Phylum (plural phyla) is the classificatory name by which we distinguish really fundamentally different animals like molluscs, nematode worms, echinoderms and chordates (chordates are mostly vertebrates plus a few odds and ends). Ancestors of two different phyla, say vertebrates and molluscs, which we see as built upon utterly different 'fundamental body plans' were once just two species within a genus. Before that, they were two geographically separated populations within one ancestral species. The implication of this widely accepted view is that, as you go back and back in geological time, the gap between any pair of animal groups becomes smaller and smaller. The further back in time you go, the closer you approach the uniting of these different kinds of animals in their single common ancestor species. Our ancestors and mollusc ancestors were once very alike. Later they were not quite so alike. Later again they had diverged further, and so on until eventually they became so different that we should call them two phyla. This general story can scarcely be doubted by any reasonable person who thinks it through, though we do not have to be committed to the view that it occurs at a uniform rate with time. It could have happened in rapid bursts.

The dramatic phrase 'Cambrian explosion' is used in two senses. It can refer to the factual observation that before the Cambrian era, just over half a billion years ago, there are few fossils. Most of the great animal phyla appear as fossils for the first time in Cambrian rocks, and this looks like a great explosion of new animals. The second meaning is the theory that the phyla actually branched off from each other during the Cambrian, even during as little as 10 million years within the Cambrian. This second idea, which I shall call the branch point explosion hypothesis, is controversial. It is compatible—just—with what I am calling the standard neo-Darwinian model of species divergence. We've already agreed that, as we trace any pair of modern phyla back in time, we eventually converge upon a common ancestor. My hunch is that, for different pairs of phyla, we'll hit the common ancestor in different geological eras: say, the common ancestor of vertebrates and molluscs at 800 million years ago, the common ancestor of vertebrates and echinoderms at 600 million years, and so on. But I could be wrong, and we can easily accommodate the branch point explosion hypothesis by saying that, for some reason (which is interesting enough to need investigating), most of our backward tracings happen to hit their respective common ancestors during the same relatively short geological period, say, between 540 million and 530 million years ago. This would have to mean that, at least near the beginning of that 10-million-year period, the ancestors of the modern phyla were nowhere near as different from each other as they Eire today. They were, after all, diverging from common ancestors at the time and were originally members of the Same species.

The extreme Gouldian view—certainly the view inspired by his rhetoric, though it is hard to tell from his own words whether he literally holds it himself—is radically different from and utterly incompatible with the standard neo-Darwinian model. It also, as I shall show, has implications which, once they are spelled out, anybody can see are absurd. It is very clearly expressed—betrayed might be a better word—in asides in Stuart Kauffman's At Home in the Universe (1995):

One might imagine that the first multicellular creatures would all be very similar, only later diversifying, from the bottom up, into different genera, families, orders, classes, and so on. That, indeed, would be the expectation of the strictest conventional Darwinist Darwin, profoundly influenced by the emerging view of geologic gradualism, proposed that all evolution occurred by the very gradual accumulation of useful variations. Thus the earliest multicellular creatures themselves ought to have diverged gradually from one another.

So fax, this is a fine summary of the orthodox neo-Darwinian view. Now, in a bizarre passage, Kauffman goes on:

But this appears to be false. One of the wonderful and puzzling features of the Cambrian explosion is that the chart was filled in from the top down. Nature suddenly sprang forth with many wildly different body plans—the phyla—elaborating on these basic designs to form the classes, orders, families, and genera ... In his book about the Cambrian explosion, Wonderful Life: The Burgess Shale and the Nature of History, Stephen Jay Gould remarks on this top-down quality of the Cambrian with wonder.

As well he might! You only have to think for one moment about what 'top down' filling in would have to mean for the animals on the ground and you immediately see how preposterous it is. 'Body plans' like the mollusc body plan, or the echinoderm body plan, are not ideal essences hanging in the sky, waiting, like designer dresses, to be adopted by real animals. Real animals is all there ever was: living, breathing, walking, eating, excreting, fighting, copulating real animals, who had to survive and who can't have been dramatically different from their real parents and grandparents. For a new body plan—a new phylum—to spring into existence, what actually has to happen on the ground is that a child is born which suddenly, out of the blue, is as different from its parents as a snail is from an earthworm. No zoologist who thinks through the implications, not even the most ardent saltationist, has ever supported any such notion. Ardent saltationists have been content to postulate the sudden bursting into existence of new species, and even that relatively modest idea has been highly controversial. When you spell out the Gouldian rhetoric into real-life practicalities, it stands revealed as the purest of bad poetic science.

Kauffman is even more explicit in a later chapter. In discussing some of his ingenious mathematical models of evolution on 'rugged fitness landscapes', Kauffman notes a pattern that he thinks

sounds a lot like the Cambrian explosion. Early on in the branching process, we find a variety of long-jump mutations that differ from the stem and from one another quite dramatically. These species have sufficient morphological differences to be categorized as founders of distinct phyla. These founders also branch, but do so via slightly closer long-jump variants, yielding branches from each founder of a phylum to dissimilar daughter species, the founders of classes. As the process continues, fitter variants are found in progressively more nearby neighborhoods, so founders of orders, families, and genera emerge in succession.

Kauffman's earlier, more technical book, The Origins of Order (1993), says something similar about life in the Cambrian:

Not only did a very large number of novel body forms originate rapidly, but the Cambrian explosion exhibited another novelty: Species which founded taxa appear to have built up the higher taxa from the top down. That is, exemplars of major phyla were present first, followed by progressive filling in at class, order, and lower taxonomic levels...

Now, one way of reading this is inoffensive to the point of obviousness. On our 'converging backwards' model it would have to be true that species splittings that are eventually going to become phylum divides would normally precede those that are destined to become divides between orders and lower taxonomic levels. But Kauffman clearly doesn't think he is saying something ordinary and obvious. This is apparent from his statement that 'the Cambrian explosion exhibited another novelty', and from his phrase 'long-jump mutations'. He thinks he is attributing to the Cambrian something revolutionary. He really does seem genuinely to intend the alternative reading, in which 'long-jump mutations' give rise, on the instant, to brand new phyla.

I hasten to emphasize that these passages of Kauffman's are embedded in a pair of books that are for the most part interesting, creative and uninfluenced by Gould. The same is true of Richard Leakey and Roger Lewin's The Sixth Extinction (1996), another recent book, admirable in most of its chapters, but sadly marred by one, 'The Mainspring of Evolution', which is explicitly and avowedly influenced by Gould. Here are a couple of relevant passages:

It was as if the facility for making evolutionary leaps that produced major functional novelties—the basis of new phyla—had somehow been lost when the Cambrian period came to an end It was as if the mainspring of evolution had lost some of its power.

Hence, evolution in Cambrian organisms could take bigger leaps, including phylum-level leaps, while later on it would be more constrained, making only modest jumps, up to the class level.

As I have written before, it is as though a gardener looked at an old oak tree and remarked, wonderingly: 'Isn't it strange that no major new boughs have appeared on this tree for many years. These days, all the new growth appears to be at the twig level!' Just think once again what a 'phylum-level leap' or even a 'modest' (modest?) class level leap would have to mean. Animals of different phyla, remember, are animals with different fundamental body plans, like molluscs and vertebrates. Or like starfish and insects. A long-jump, phylum level mutation would have to mean that a couple of parents belonging to one phylum mated and gave birth to a child belonging to a different phylum. The difference between parent and offspring would have to be on the same scale as the difference between a snail and a lobster, or a starfish and a codfish. A class level leap would be equivalent to a pair of birds giving birth to a mammal. Picture the parents gazing wonderingly into the nest at what they have produced, and the full comedy of the notion becomes apparent.

My assurance in ridiculing these ideas is not based simply upon knowledge of the facts of modern animals. Obviously if it were just that, one could retort that things were different in the Cambrian. No, the argument against Kauffman's long jumps, or Leakey and Lewin's phylum level leaps, is a theoretical one, and an extremely strong one. It is this. Even if mutations on this gigantic scale occurred, the products would not have survived. This is fundamentally because, as I have said before, however many ways there may be of being alive, there are almost infinitely more ways of being dead. A small mutation, representing a minor step away from a parent which has proved its ability to survive by virtue of being a parent, has a good chance of surviving for the same reason, and it may even be an improvement. A gigantic, phylum level mutation is a leap into the wild blue yonder. I said that the long-jump mutation we are talking about would be of the same magnitude as a mutation from a mollusc to an insect. But it would never, of course, have been a jump from a mollusc to an insect. An insect is a highly tuned piece of survival machinery. If a mollusc parent gave birth to a new phylum, the leap would have been a random leap, like any other mutation. And the chance that a random leap of that magnitude would produce an insect, or anything with the faintest chance of surviving, is small enough to be discounted totally. The chance of its being viable is impossibly small, no matter how empty the ecosystem, how wide open the niches. A phylum level leap would be a mess.

I do not believe the authors I am quoting really believe what their printed words undoubtedly appear to be saying. I think they were simply intoxicated by Gould's rhetoric and didn't think it through. The whole point of quoting them in this chapter is to illustrate the power to mislead that a skilled poet can unwittingly exert, especially if he has first misled himself. And the poetry of the Cambrian as a blissful dawn of innovation is undoubtedly beguiling. Kauffman gets completely carried away by it:

Soon after multicelled forms were invented, a grand burst of evolutionary novelty thrust itself outward One almost gets the sense of multicellular life gleefully trying out all its possible ramifications, in a kind of wild dance of heedless exploration.

At Home in the Universe (1995)

Yes. One does get exactly that sense. But one gets it from Gould's rhetoric, not from the facts of Cambrian fossils nor from sober reasoning about evolutionary principles.

If scientists of the calibre of Kauffman, Leakey and Lewin can be seduced by bad poetic science, what chance has the non-specialist? Daniel Dennett has told me of a conversation with a philosopher colleague who had read Wonderful Life as arguing that the Cambrian phyla did not have a common ancestor—that they had sprung up as independent origins of life! When Dennett assured him that this was not Gould's intention, his colleague's response was, 'Well then, what is all the fuss about?'

Excellence in writing is a double-edged sword, as the distinguished evolutionary scientist John Maynard Smith has noted, in the New York Review of Books, November 1995:

Gould occupies a rather curious position, particularly on his side of the Atlantic. Because of the excellence of his essays, he has come to be seen by non-biologists as the preeminent evolutionary theorist. In contrast, the evolutionary biologists with whom I have discussed his work tend to see him as a man whose ideas are so confused as to be hardly worth bothering with, but as one who should not be publicly criticized because he is at least on our side against the creationists. All this would not matter, were it not that he is giving non-biologists a largely false picture of the state of evolutionary theory.

Maynard Smith was reviewing Dennett's book Darwin's Dangerous Idea (1995), which contains a devastating and, one might hope, terminal critique of Gould's influence on evolutionary thinking.

What really happened in the Cambrian? Simon Conway Morris of Cambridge University is, as Gould fulsomely acknowledges, one of the three leading modern investigators of the Burgess Shale, the Cambrian fossil bed which is the subject of Wonderful Life. Conway Morris has recently published his own fascinating book on the subject, The Crucible of Creation (1998), which is critical of almost every aspect of Gould's view. Like Conway Morris, I don't think there's any good reason to think that the process of evolution was different in the Cambrian from the way it is today. But there is no doubt that a large number of major animal groups are seen in the fossil record for the first time in the Cambrian. The obvious hypothesis has occurred to many people. Perhaps several groups of animals evolved hard, fossilizable skeletons around the same time and perhaps for the same reason. One possibility is an evolutionary arms race between predators and prey, but there are other ideas like a dramatic change in the chemistry of the atmosphere. Conway Morris finds no support at all for the poetic idea of an exuberant and extravagant flowering of life in a wild dance of Cambrian diversity and disparity, subsequently pruned to today's more limited repertoire of animal types. If anything, the reverse seems to be true, as most evolutionists would expect.

Where does that leave the question of the timing of the branch points of the major phyla? Recall that this is a separate question from the undoubted Cambrian explosion of fossil availability. The controversial matter is whether the branch points in the divergence of all the major phyla are concentrated in the Cambrian—the branch point explosion hypothesis. I said standard neo-Darwinism was compatible with this hypothesis. But I still don't think it is at all likely.

One possible way to tackle the question is by looking at molecular clocks. 'Molecular clock' refers to the observation that certain biological molecules change at a rather fixed rate over the millions of years. If you accept this, you can take blood from any two modern animals and calculate how long ago their common ancestor lived. Some recent molecular clock studies have pushed the branch points of various pairs of phyla deep into the Precambrian era. If these studies are right, the whole rhetoric of an evolutionary explosion becomes superfluous. But there is controversy over the interpretation of molecular clock results so far back in deep time, and we should wait for more evidence.

Meanwhile, there is a logical argument which I can assert with more confidence. The only evidence in favour of the branch point explosion hypothesis is negative: there aren't any fossils of many of the phyla before the Cambrian. But those fossil animals that have no fossil ancestors must have had ancestors of some kind. They can't have sprung from nothing. Therefore there must have been ancestors that didn't fossilize, absence of fossils does not mean absence of animals. The only question that remains is whether the missing ancestors going back to the branch points, who must have existed, were all compressed into the Cambrian, or whether they were strung out through the previous hundreds of millions of years. Since the only reason to suppose that they were compressed into the Cambrian is the absence of fossils, and since we have just proved logically the irrelevance of that absence, I conclude that there is no good reason at all to favour the branch point explosion hypothesis. Doubtless it has great poetic appeal.