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.
Richard-Dawkins-Unweaving-the-Rainbow
Statistical judgement means steering a middle course between the two kinds of error.
There is a type 5 error in which your mind goes totally blank whenever you try to remember which is which of type 1 and type 2.
I still look them up after a lifetime of use.
Where it matters, therefore, I shall use the more easily remembered names, false positive and false negative.
I also, by the way, frequently make mistakes in arithmetic.
In practice I should never dream of doing a statistical test from first principles as I did for the hypothetical handwriting case.
I'd always look up in a table that somebody else - preferably a computer - had calculated.
Skinner's superstitious pigeons made false positive errors. There was in fact no pattern in their world that truly connected their actions to the deliveries of the reward mechanism. But they behaved as if they had detected such a pattern. One pigeon 'thought' (or behaved as if it thought) that left stepping caused the reward mechanism to deliver. Another 'thought' that thrusting its head into the corner had the same beneficial effect. Both were making false positive errors. A false negative error is made by a pigeon in a Skinner box who never notices that a peck at the key yields food if the red light is on, but that a peck when the blue light
is on punishes by switching the mechanism off for ten minutes. There is a genuine pattern waiting to be detected in the little world of this Skinner box, but our hypothetical pigeon does not detect it. It pecks indiscriminately to both colours, and therefore gets a reward less frequently than it could.
A false positive error is made by a farmer who thinks that sacrificing to the gods brings longed-for rain. In fact, I presume (although I haven't investigated the matter experimentally), there is no such pattern in his world, but he does not discover this and persists in his useless and wasteful sacrifices. A false negative error is made by a farmer who fails to notice that there is a pattern in the world relating manuring of a field to the subsequent crop yield of that field. Good farmers steer a middle way between type 1 and type 2 errors.
It is my thesis that all animals, to a greater or lesser extent, behave as intuitive statisticians, choosing a middle course between type 1 and type 2 errors. Natural selection penalizes both type 1 and type 2 errors, but the penalties are not symmetrical and no doubt vary with the different ways of life of species. A stick caterpillar looks so like the twig it is sitting on that we cannot doubt that natural selection has shaped it to resemble a twig. Many caterpillars died to produce this beautiful result. They died because they did not sufficiently resemble a twig. Birds, or other predators, found them out. Even some very good twig mimics must have been found out. How else did natural selection push evolution towards the pitch of perfection that we see? But, equally, birds must many times have missed caterpillars because they resembled twigs, in some cases only slightly. Any prey animal, no matter how well camouflaged, can be detected by predators under ideal seeing conditions. Equally, any prey animal, no matter how poorly camouflaged, can be missed by predators under bad seeing conditions. Seeing conditions can vary with angle (a predator may spot a well-camouflaged animal when looking straight at it, but will miss a poorly camouflaged animal out of the corner of its eye). They can vary with light intensity (a prey may be overlooked at twilight, whereas it would be seen at noon). They can vary with distance (a prey which would be seen at six inches range may be overlooked at a range of 100 yards).
Imagine a bird cruising around a wood, looking for prey. It is surrounded by twigs, a very few of which might be edible caterpillars. The problem is to decide. We can assume that the bird could guarantee to tell whether an apparent twig was actually a caterpillar if it approached the twig really close and subjected it to a minute, concentrated examination in a good light. But there isn't time to do that for all twigs. Small birds with high turnover metabolism have to find food alarmingly often in order to stay alive. Any bird that scanned every individual twig with the equivalent of a magnifying glass would die of starvation before it found its first caterpillar. Efficient searching demands a faster, more cursory and rapid scanning, even though this carries a risk of missing some food. The bird has to strike a balance. Too cursory and it will never find anything. Too detailed and it will detect every caterpillar it looks at, but it will look at too few, and starve.
It is easy to apply the language of type 1 and type 2 errors. A false negative is committed by a bird that sails by a caterpillar without giving it a closer look. A false positive is committed by a bird that zooms in on a suspected caterpillar, only to discover that it is really a twig. The penalty for a false positive is the time and energy wasted flying in for the close inspection: not serious on any one occasion, but it could mount up fatally. The penalty for a false negative is missing a meal. No bird outside Cloud Cuckooland can hope to be free of all type 1 and type 2 errors. Individual birds will be programmed by natural selection to adopt some compromise policy calculated to achieve an optimum intermediate level of false positives and false negatives. Some birds may be biased towards type 1 errors, others towards the opposite extreme. There will be some intermediate setting which is best, and natural selection will steer evolution towards it.
Which intermediate setting is best will vary from species to species. In
our example it will also depend upon conditions in the wood, for example, the size of the caterpillar population in relation to the number of twigs. These conditions may change from week to week. Or they may vary from wood to wood. Birds may be programmed to learn to adjust their policy
as a result of their statistical experience. Whether they learn or not, successfully hunting animals must usually behave as if they are good statisticians. (I hope it is not necessary, by the way, to plod through the usual disclaimer: No, no, the birds aren't consciously working it out with calculator and probability tables. They are behaving as if they were calculating p-values. They are no more aware of what a p-value means than you are aware of the equation for a parabolic trajectory when you catch a cricket ball or baseball in the outfield. )
Angler fish take advantage of the gullibility of little fish such as gobies. But that is an unfairly value-laden way of putting it. It would be better not to speak of gullibility and say that they exploit the inevitable difficulty the little fish have in steering between type 1 and type 2 errors. The little fish themselves need to eat. What they eat varies, but it often includes small wriggling objects such as worms or shrimps. Their eyes and nervous systems are tuned to wriggling things. They look for wriggling movement and if they see it they pounce. The angler fish exploits this tendency. It has a long fishing rod, evolved from a modified spine, commandeered by natural selection from its original location at the front of the dorsal fin. The angler fish itself is highly camouflaged and it sits motionless on the sea bottom for hours at a time, blending perfectly with the weeds and rocks. The only part of it which is conspicuous is a 'bait', which looks like a worm, a shrimp or a small fish, at the end of its fishing rod. In some deep-sea species the bait is even luminous. In any case, it seems to wriggle like something worth eating
when the angler waves its rod. A possible prey fish say, a goby, is attracted. The angler 'plays' its prey for a little while to hook its attention, then casts the bait down into the still unsuspected region in front of its own invisible mouth, and the little fish often follows. Suddenly that huge mouth is invisible no longer. It gapes massively, there is a violent inrushing of water, engulfing every floating object in the vicinity, and the little fish has pursued its last worm.
From the point of view of a hunting goby, any worm may be overlooked or it may be seen. Once the worm has been detected, it may turn out to be a real worm or an angler fish's lure, and the unfortunate fish is faced with a dilemma. A false negative error would be to refrain from attacking a perfectly good worm for fear that it might be an angler fish lure. A false positive error would be to attack a worm, only to discover that it is really a lure. Once again, it is impracticable in the real world to get it right all the time. A fish that is too risk-averse will starve because it never attacks worms. A fish that is too foolhardy won't starve but it may be eaten. The optimum in this case may not be halfway between. More surprisingly, the optimum may be one of the extremes. It is possible that angler fish are sufficiently rare that natural selection favours the extreme policy of attacking all apparent worms. I am fond of a remark of the philosopher and psychologist William James on human angling:
There are more worms unattached to hooks than impaled upon them; therefore, on the whole, says Nature to her fishy children, bite at every worm and take your chances. (1910)
Like all other animals, and even plants, humans can and must behave as intuitive statisticians. The difference with us is that we can do our calculations twice over. The first time intuitively, as though we were birds or fish. And then again explicitly, with pencil and paper or computer. It is tempting to say that the pencil and paper way gets the right answer, so long as we don't make some publicly detectable blunder like adding in the date, whereas the intuitive way may yield the wrong answer. But there strictly is no 'right' answer, even in the case of pencil and paper statistics. There may be a right way to do the sums, to calculate the p-value, but the criterion, or threshold p-value, that we demand before choosing a particular action is still our decision and it depends upon our aversion to risk. If the penalty for making a false positive error is much greater than the penalty for making a false negative error, we should adopt a cautious, conservative threshold; almost never try a 'worm' for fear of the consequences. Conversely, if the risk-asymmetry is opposite, we should rush in and try every 'worm' that is going: it is unlikely to matter if we keep tasting false worms so we may as well have a go.
Taking on board the need to steer between false positive and false negative errors, let me return to uncanny coincidence and the calculation of the probability that it would have happened anyway. If I dream of a long-forgotten friend who dies the same night, I am tempted, like anyone else, to see meaning or pattern in the coincidence. I really have to force myself to remember that quite a few people die every night, masses of people dream every night, they quite often dream that people die, and coincidences like this are probably happening to several hundred people in the world every night. Even as I think this through, my own intuition cries out that there must be meaning in the coincidence because it has happened to me. If it is true that intuition is, in this case, making a false positive error, we need to come up with a satisfactory explanation for why human intuition errs in this direction. As Darwinians, we should be alive to the possible pressures towards erring on the type 1 or the type 2. side of the divide.
As a Darwinian, I want to suggest that our willingness to be impressed at apparently uncanny coincidence (which is a case of our willingness to see pattern where there is none) is related to the typical population size of our ancestors and the relative poverty of their everyday experience. Anthropology, fossil evidence and the study of other apes all suggest that our ancestors, for much of the past few million years, probably lived in either small roving bands or small villages. Either of these would mean that the number of friends and acquaintances that our ancestors would ordinarily meet and talk to with any frequency was not more than a few dozen. A prehistoric villager could expect to hear stories of startling coincidence in proportion to this small number of acquaintances. If the coincidence happened to somebody not in his village, he wouldn't hear the story. So our brains became calibrated to detect pattern and gasp with astonishment at a level of coincidence which would actually be quite modest if our catchment area of friends and acquaintances had been large.
Nowadays, our catchment area is large, especially because of newspapers, radio and other vehicles of mass news circulation. I've already spelled out the argument. The very best and most spine-creeping coincidences have the opportunity to circulate, in the form of bated-breath stories, over a
far wider audience than was ever possible in ancestral times. But, I am now conjecturing, our brains are calibrated by ancestral natural selection to expect a much more modest level of coincidence, calibrated under small village conditions. So we are impressed by coincidences because of a miscalibrated gasp threshold. Our subjective petwhacs have been calibrated by natural selection in small villages, and, as is the case with so much of modern life, the calibration is now out of date.
A similar argument could be used to explain why we are so hysterically risk-averse to hazards that are much publicized in the newspapers - perhaps anxious parents who imagine ravening paedophiles lurking behind every lamp post on their children's walk from school are 'miscalibrated'.
I guess that there may be another, particular effect pushing in the same direction. I suspect that our individual lives under modern conditions are richer in experiences per hour than were ancestral lives. We don't just get up in the morning, scratch a living in the same way as yesterday, eat a meal or two and go to sleep again. We read books and magazines, we watch television, we travel at high speed to new places, we pass thousands of people in the street as we walk to work. The number of faces we see, the number of different situations we are exposed to, the number of separate things that happen to us, is much greater than for our village ancestors. This means that the number of opportunities for coincidence is greater for each one of us than it would have been for our ancestors, and consequently greater than our brains are calibrated to assess. This is an additional effect, over and above the population size effect that I have already noted.
With respect to both these effects, it is theoretically possible for us to recalibrate ourselves, learn to adjust our gasp threshold to a level more appropriate to modem populations and modern richnesses of experience. But this seems to be revealingly difficult even for sophisticated scientists and mathematicians. The fact that we still do gasp when we do, that clairvoyants and mediums and psychics and astrologers manage to make such a nice living out of us, all suggests that we do not, on the whole, learn to recalibrate ourselves. It suggests that the parts of our brains responsible for doing intuitive statistics are still back in the stone age.
The same may be true of intuition generally. In The Unnatural Nature of Science (1992), the distinguished embryologist Lewis Wolpert has argued that science is difficult because it is more or less systematically counter- intuitive. This is contrary to the view of T. H. Huxley (Darwin's Bulldog) who saw science as 'nothing but trained and organized common sense, differing from the latter only as a veteran may differ from a raw recruit'. For Huxley, the methods of science 'differ from those of common sense only as far as the guardsman's cut and thrust differ from the manner in which a savage wields his club'. Wolpert insists that science is deeply paradoxical and surprising, an affront to common sense rather than an extension of it, and he makes a good case. For example, every time you drink a glass of water you are imbibing at least one molecule that passed through the bladder of Oliver Cromwell. This follows by extrapolation from Wolpert's observation that 'there are many more molecules in a glass of water than there are glasses of water in the sea'. Newton's law
that objects stay in motion unless positively stopped is counter-intuitive. So is Galileo's discovery that, when there is no air resistance, light objects fall at the same rate as heavy objects. So is the fact that solid matter, even a hard diamond, consists almost entirely of empty space. Steven Pinker gives an illuminating discussion of the evolutionary origins of our physical intuitions in How the Mind Works (1998).
More profoundly difficult are the conclusions of quantum theory, overwhelmingly supported by experimental evidence to a stupefyingly convincing number of decimal places, yet so alien to the evolved human mind that even professional physicists don't understand them in their intuitive thoughts. It seems to be not just our intuitive statistics but our very minds themselves that are back in the stone age.
8
HUGE CLOUDY SYMBOLS OF A HIGH ROMANCE
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.
WILLIAM SHAKESPEARE,
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 homoeopathically 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 5oo 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 1959 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 they 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 2. ? 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 are 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 woman'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 palaeontologist 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 palaeontology' 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 palaeontology 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 palaeontology 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 palaeontologists 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.
Skinner's superstitious pigeons made false positive errors. There was in fact no pattern in their world that truly connected their actions to the deliveries of the reward mechanism. But they behaved as if they had detected such a pattern. One pigeon 'thought' (or behaved as if it thought) that left stepping caused the reward mechanism to deliver. Another 'thought' that thrusting its head into the corner had the same beneficial effect. Both were making false positive errors. A false negative error is made by a pigeon in a Skinner box who never notices that a peck at the key yields food if the red light is on, but that a peck when the blue light
is on punishes by switching the mechanism off for ten minutes. There is a genuine pattern waiting to be detected in the little world of this Skinner box, but our hypothetical pigeon does not detect it. It pecks indiscriminately to both colours, and therefore gets a reward less frequently than it could.
A false positive error is made by a farmer who thinks that sacrificing to the gods brings longed-for rain. In fact, I presume (although I haven't investigated the matter experimentally), there is no such pattern in his world, but he does not discover this and persists in his useless and wasteful sacrifices. A false negative error is made by a farmer who fails to notice that there is a pattern in the world relating manuring of a field to the subsequent crop yield of that field. Good farmers steer a middle way between type 1 and type 2 errors.
It is my thesis that all animals, to a greater or lesser extent, behave as intuitive statisticians, choosing a middle course between type 1 and type 2 errors. Natural selection penalizes both type 1 and type 2 errors, but the penalties are not symmetrical and no doubt vary with the different ways of life of species. A stick caterpillar looks so like the twig it is sitting on that we cannot doubt that natural selection has shaped it to resemble a twig. Many caterpillars died to produce this beautiful result. They died because they did not sufficiently resemble a twig. Birds, or other predators, found them out. Even some very good twig mimics must have been found out. How else did natural selection push evolution towards the pitch of perfection that we see? But, equally, birds must many times have missed caterpillars because they resembled twigs, in some cases only slightly. Any prey animal, no matter how well camouflaged, can be detected by predators under ideal seeing conditions. Equally, any prey animal, no matter how poorly camouflaged, can be missed by predators under bad seeing conditions. Seeing conditions can vary with angle (a predator may spot a well-camouflaged animal when looking straight at it, but will miss a poorly camouflaged animal out of the corner of its eye). They can vary with light intensity (a prey may be overlooked at twilight, whereas it would be seen at noon). They can vary with distance (a prey which would be seen at six inches range may be overlooked at a range of 100 yards).
Imagine a bird cruising around a wood, looking for prey. It is surrounded by twigs, a very few of which might be edible caterpillars. The problem is to decide. We can assume that the bird could guarantee to tell whether an apparent twig was actually a caterpillar if it approached the twig really close and subjected it to a minute, concentrated examination in a good light. But there isn't time to do that for all twigs. Small birds with high turnover metabolism have to find food alarmingly often in order to stay alive. Any bird that scanned every individual twig with the equivalent of a magnifying glass would die of starvation before it found its first caterpillar. Efficient searching demands a faster, more cursory and rapid scanning, even though this carries a risk of missing some food. The bird has to strike a balance. Too cursory and it will never find anything. Too detailed and it will detect every caterpillar it looks at, but it will look at too few, and starve.
It is easy to apply the language of type 1 and type 2 errors. A false negative is committed by a bird that sails by a caterpillar without giving it a closer look. A false positive is committed by a bird that zooms in on a suspected caterpillar, only to discover that it is really a twig. The penalty for a false positive is the time and energy wasted flying in for the close inspection: not serious on any one occasion, but it could mount up fatally. The penalty for a false negative is missing a meal. No bird outside Cloud Cuckooland can hope to be free of all type 1 and type 2 errors. Individual birds will be programmed by natural selection to adopt some compromise policy calculated to achieve an optimum intermediate level of false positives and false negatives. Some birds may be biased towards type 1 errors, others towards the opposite extreme. There will be some intermediate setting which is best, and natural selection will steer evolution towards it.
Which intermediate setting is best will vary from species to species. In
our example it will also depend upon conditions in the wood, for example, the size of the caterpillar population in relation to the number of twigs. These conditions may change from week to week. Or they may vary from wood to wood. Birds may be programmed to learn to adjust their policy
as a result of their statistical experience. Whether they learn or not, successfully hunting animals must usually behave as if they are good statisticians. (I hope it is not necessary, by the way, to plod through the usual disclaimer: No, no, the birds aren't consciously working it out with calculator and probability tables. They are behaving as if they were calculating p-values. They are no more aware of what a p-value means than you are aware of the equation for a parabolic trajectory when you catch a cricket ball or baseball in the outfield. )
Angler fish take advantage of the gullibility of little fish such as gobies. But that is an unfairly value-laden way of putting it. It would be better not to speak of gullibility and say that they exploit the inevitable difficulty the little fish have in steering between type 1 and type 2 errors. The little fish themselves need to eat. What they eat varies, but it often includes small wriggling objects such as worms or shrimps. Their eyes and nervous systems are tuned to wriggling things. They look for wriggling movement and if they see it they pounce. The angler fish exploits this tendency. It has a long fishing rod, evolved from a modified spine, commandeered by natural selection from its original location at the front of the dorsal fin. The angler fish itself is highly camouflaged and it sits motionless on the sea bottom for hours at a time, blending perfectly with the weeds and rocks. The only part of it which is conspicuous is a 'bait', which looks like a worm, a shrimp or a small fish, at the end of its fishing rod. In some deep-sea species the bait is even luminous. In any case, it seems to wriggle like something worth eating
when the angler waves its rod. A possible prey fish say, a goby, is attracted. The angler 'plays' its prey for a little while to hook its attention, then casts the bait down into the still unsuspected region in front of its own invisible mouth, and the little fish often follows. Suddenly that huge mouth is invisible no longer. It gapes massively, there is a violent inrushing of water, engulfing every floating object in the vicinity, and the little fish has pursued its last worm.
From the point of view of a hunting goby, any worm may be overlooked or it may be seen. Once the worm has been detected, it may turn out to be a real worm or an angler fish's lure, and the unfortunate fish is faced with a dilemma. A false negative error would be to refrain from attacking a perfectly good worm for fear that it might be an angler fish lure. A false positive error would be to attack a worm, only to discover that it is really a lure. Once again, it is impracticable in the real world to get it right all the time. A fish that is too risk-averse will starve because it never attacks worms. A fish that is too foolhardy won't starve but it may be eaten. The optimum in this case may not be halfway between. More surprisingly, the optimum may be one of the extremes. It is possible that angler fish are sufficiently rare that natural selection favours the extreme policy of attacking all apparent worms. I am fond of a remark of the philosopher and psychologist William James on human angling:
There are more worms unattached to hooks than impaled upon them; therefore, on the whole, says Nature to her fishy children, bite at every worm and take your chances. (1910)
Like all other animals, and even plants, humans can and must behave as intuitive statisticians. The difference with us is that we can do our calculations twice over. The first time intuitively, as though we were birds or fish. And then again explicitly, with pencil and paper or computer. It is tempting to say that the pencil and paper way gets the right answer, so long as we don't make some publicly detectable blunder like adding in the date, whereas the intuitive way may yield the wrong answer. But there strictly is no 'right' answer, even in the case of pencil and paper statistics. There may be a right way to do the sums, to calculate the p-value, but the criterion, or threshold p-value, that we demand before choosing a particular action is still our decision and it depends upon our aversion to risk. If the penalty for making a false positive error is much greater than the penalty for making a false negative error, we should adopt a cautious, conservative threshold; almost never try a 'worm' for fear of the consequences. Conversely, if the risk-asymmetry is opposite, we should rush in and try every 'worm' that is going: it is unlikely to matter if we keep tasting false worms so we may as well have a go.
Taking on board the need to steer between false positive and false negative errors, let me return to uncanny coincidence and the calculation of the probability that it would have happened anyway. If I dream of a long-forgotten friend who dies the same night, I am tempted, like anyone else, to see meaning or pattern in the coincidence. I really have to force myself to remember that quite a few people die every night, masses of people dream every night, they quite often dream that people die, and coincidences like this are probably happening to several hundred people in the world every night. Even as I think this through, my own intuition cries out that there must be meaning in the coincidence because it has happened to me. If it is true that intuition is, in this case, making a false positive error, we need to come up with a satisfactory explanation for why human intuition errs in this direction. As Darwinians, we should be alive to the possible pressures towards erring on the type 1 or the type 2. side of the divide.
As a Darwinian, I want to suggest that our willingness to be impressed at apparently uncanny coincidence (which is a case of our willingness to see pattern where there is none) is related to the typical population size of our ancestors and the relative poverty of their everyday experience. Anthropology, fossil evidence and the study of other apes all suggest that our ancestors, for much of the past few million years, probably lived in either small roving bands or small villages. Either of these would mean that the number of friends and acquaintances that our ancestors would ordinarily meet and talk to with any frequency was not more than a few dozen. A prehistoric villager could expect to hear stories of startling coincidence in proportion to this small number of acquaintances. If the coincidence happened to somebody not in his village, he wouldn't hear the story. So our brains became calibrated to detect pattern and gasp with astonishment at a level of coincidence which would actually be quite modest if our catchment area of friends and acquaintances had been large.
Nowadays, our catchment area is large, especially because of newspapers, radio and other vehicles of mass news circulation. I've already spelled out the argument. The very best and most spine-creeping coincidences have the opportunity to circulate, in the form of bated-breath stories, over a
far wider audience than was ever possible in ancestral times. But, I am now conjecturing, our brains are calibrated by ancestral natural selection to expect a much more modest level of coincidence, calibrated under small village conditions. So we are impressed by coincidences because of a miscalibrated gasp threshold. Our subjective petwhacs have been calibrated by natural selection in small villages, and, as is the case with so much of modern life, the calibration is now out of date.
A similar argument could be used to explain why we are so hysterically risk-averse to hazards that are much publicized in the newspapers - perhaps anxious parents who imagine ravening paedophiles lurking behind every lamp post on their children's walk from school are 'miscalibrated'.
I guess that there may be another, particular effect pushing in the same direction. I suspect that our individual lives under modern conditions are richer in experiences per hour than were ancestral lives. We don't just get up in the morning, scratch a living in the same way as yesterday, eat a meal or two and go to sleep again. We read books and magazines, we watch television, we travel at high speed to new places, we pass thousands of people in the street as we walk to work. The number of faces we see, the number of different situations we are exposed to, the number of separate things that happen to us, is much greater than for our village ancestors. This means that the number of opportunities for coincidence is greater for each one of us than it would have been for our ancestors, and consequently greater than our brains are calibrated to assess. This is an additional effect, over and above the population size effect that I have already noted.
With respect to both these effects, it is theoretically possible for us to recalibrate ourselves, learn to adjust our gasp threshold to a level more appropriate to modem populations and modern richnesses of experience. But this seems to be revealingly difficult even for sophisticated scientists and mathematicians. The fact that we still do gasp when we do, that clairvoyants and mediums and psychics and astrologers manage to make such a nice living out of us, all suggests that we do not, on the whole, learn to recalibrate ourselves. It suggests that the parts of our brains responsible for doing intuitive statistics are still back in the stone age.
The same may be true of intuition generally. In The Unnatural Nature of Science (1992), the distinguished embryologist Lewis Wolpert has argued that science is difficult because it is more or less systematically counter- intuitive. This is contrary to the view of T. H. Huxley (Darwin's Bulldog) who saw science as 'nothing but trained and organized common sense, differing from the latter only as a veteran may differ from a raw recruit'. For Huxley, the methods of science 'differ from those of common sense only as far as the guardsman's cut and thrust differ from the manner in which a savage wields his club'. Wolpert insists that science is deeply paradoxical and surprising, an affront to common sense rather than an extension of it, and he makes a good case. For example, every time you drink a glass of water you are imbibing at least one molecule that passed through the bladder of Oliver Cromwell. This follows by extrapolation from Wolpert's observation that 'there are many more molecules in a glass of water than there are glasses of water in the sea'. Newton's law
that objects stay in motion unless positively stopped is counter-intuitive. So is Galileo's discovery that, when there is no air resistance, light objects fall at the same rate as heavy objects. So is the fact that solid matter, even a hard diamond, consists almost entirely of empty space. Steven Pinker gives an illuminating discussion of the evolutionary origins of our physical intuitions in How the Mind Works (1998).
More profoundly difficult are the conclusions of quantum theory, overwhelmingly supported by experimental evidence to a stupefyingly convincing number of decimal places, yet so alien to the evolved human mind that even professional physicists don't understand them in their intuitive thoughts. It seems to be not just our intuitive statistics but our very minds themselves that are back in the stone age.
8
HUGE CLOUDY SYMBOLS OF A HIGH ROMANCE
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.
WILLIAM SHAKESPEARE,
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 homoeopathically 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 5oo 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 1959 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 they 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 2. ? 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 are 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 woman'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 palaeontologist 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 palaeontology' 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 palaeontology 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 palaeontology 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 palaeontologists 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.
