I suspect that, on a less grand scale, poetic science bedevils medicine too. When my father, many years ago, developed a duodenal ulcer, the doctor told him he had to eat milk puddings and other mild, gentle foods. Later advice negates this. I suspect that the advice stemmed from the ‘poetic’ association of ‘milky’ with such attributes as ‘mild’, ‘gentle’ and ‘soft’ rather than from actual evidence. Poetic medicine! And today, if you want to lose weight you are encouraged not to eat butter, cream and other fatty foods. Again, is this advice based on evidence? Or is it in part at least a ‘poetic’ association with the word ‘fat’?
I love the poetry of science in a good sense. That’s why this book is called Science in the Soul. But there’s bad poetry as well as good.
* * *
*1 In 1982, one hundred years after Charles Darwin’s death, his old university of Cambridge convened a centennial conference. What follows is a slightly edited version of the speech I gave at the conference, which appeared as a chapter in the book of proceedings, Evolution from Molecules to Men.
*2 I am astonished when I occasionally meet biologists who seem not to see the force of this. For example, the great Japanese geneticist Motoo Kimura was the main architect of the neutral theory of evolution. He was probably right that the majority of changes in gene frequency in populations (i.e. evolutionary changes) are not caused by natural selection but are neutral: new mutations come to dominate the population not because they are advantageous but because of random drift. The introduction to his great book The Neutral Theory of Molecular Evolution makes the concession that ‘the theory does not deny the role of natural selection in determining the course of adaptive evolution’. But according to John Maynard Smith, Kimura was emotionally reluctant to make even this modest concession – so reluctant, indeed, that he couldn’t bear to write it himself and asked his American colleague James Crow to write that one sentence for him! Kimura, and some other enthusiasts for the neutral theory, seem not to appreciate the importance of the functional near-perfection of biological adaptation. It’s as though they’ve never seen a stick insect, a flying albatross, or a spider web. For them, the illusion of design is a trivial and rather dubious add-on, whereas for me and for those naturalists from whom I have learned (including Darwin himself) the complex perfection of biological design is the very core and centre of the life sciences. For us, the evolutionary changes that interested Kimura amount to resetting text in a different font. For us, what matters is not whether the text is written in Times New Roman or Helvetica. What matters is what the words mean. Kimura is probably right that only a minority of evolutionary changes are adaptive. But, for pity’s sake, it is the minority that matters!
*3 Scientific experiments, especially in the biological sciences, are continually battling the suspicion that the result obtained might just be luck. Say a hundred patients are given an experimental medicine and compared with another hundred patients given a ‘control’, dummy pills that look the same but lack the active ingredient. If ninety of the experimental patients improve but only twenty of the controls, how do you know whether it is the drug that did it? Could it just be luck? Statistical tests exist to compute the probability that, if the drug really were doing nothing, you could have got the result you did get (or an even ‘better’ result) by luck. The ‘P value’ is that probability, and the lower it is, the less likely the result is to have been a matter of luck. Results with P values of 1 per cent or less are customarily taken as evidence, but that cut-off point is arbitrary. P values of 5 per cent may be taken as suggestive. For results that seem very surprising, for example an apparent demonstration of telepathic communication, a P value much lower than 1 per cent would be demanded.e demanded. demanded.demanded.emanded.manded.anded.nded.ded.ed.d..
*4 In a wild state, that is, where refined sugar doesn’t exist except in the rare and painfully won case of honey. As it happens, the sweet tooth was an unfortunate example to have chosen because, in our domesticated world, the taste for sugar does not improve our chances of survival.
*5 I later tried to make this idea more vivid, using the phrase ‘Genetic Book of the Dead’, referred to in several other essays in this collection.
*6 The psychologist B. F. Skinner was keen to emphasize the same point.
*7 There wasn’t time during my Cambridge lecture to define these two historic views of how embryology might work; and the Cambridge audience commemorating Darwin wouldn’t have needed the definition anyway. Preformationists propose that each generation contains the form of the next, either literally (a miniature body curled up in sperm or egg) or in coded form, as some kind of blueprint. Epigenesis means that each generation contains instructions for making the next generation, not as a blueprint but as something akin to a recipe or computer program. One could imagine a planet where embryology was preformationistic, as follows. The body of the parent is scanned, slice by slice, to build up instructions delivered to something equivalent to a 3D printer which then ‘prints’ the child, a copy of the parent’s body; this copy then, if necessary, ‘inflates’ to full size. That isn’t how embryology works on our planet, but it is the kind of way embryology would have to work for the hypothetical tiger-striped alien. Our kind of embryology on this planet is epigenetic; DNA is not a blueprint, contrary to most biology textbooks. It is a series of instructions, like a computer program, or a recipe or a sequence of origami paper-folds which, when followed, yields a body. Blueprint embryologies, if they exist, would be reversible, just as one can reconstruct the original architect plans by making measurements on a house. In no sense whatsoever is the body of the parent copied to make the child. Rather, the genes that made the body of the parent are copied (half of them, together with half from the other parent), and handed over as instructions to make the body of the next generation, and as unadulterated instructions to pass on to the grandchild generation. Bodies don’t beget bodies. DNA begets bodies, and DNA begets DNA.
*8 Nowadays I’d have a stab at formulating it. For a start, it would be vulnerable to the problem already mentioned about wear and tear. A ‘scan’ of the parent’s body would faithfully reproduce every scar, broken limb and missing foreskin, along with ‘good’ acquisitions such as toughened soles and learned wisdom. Once again there would be a need for a selective choice of ‘good’ acquisitions versus scars and the like. And what could the ‘selector’ be but some version of what Darwin proposed?
*9 I later used the metaphor of Climbing Mount Improbable in the book of that name. A complex piece of well-designed machinery such as an eye sits high on a peak of Mount Improbable. One side of the mountain is a sheer precipice, impossible to scale in a single leap – saltation. But on the other side of the mountain is a gentle slope, easy to climb simply by placing one foot in front of the other.
*10 Punctuated equilibrium, which briefly became familiar enough to be affectionately abbreviated to ‘punk eek’, was a theory advanced by the distinguished paleontologists Niles Eldredge and Stephen Jay Gould to account for apparent jumpiness of the fossil record. Unfortunately, partly abetted by Gould’s persuasive but misleading rhetoric, the phrase later came to confuse three entirely different kinds of jump: first, macro-mutations or saltations (mutations of large effect, producing in extreme cases ‘monstrosities’ or ‘hopeful monsters’); second, mass extinctions (like the sudden demise of the dinosaurs which cleared the stage for the mammals); and third (the meaning Eldredge and Gould intended as their original contribution) rapid gradualism. Eldredge and Gould together with some other paleontologists suggested, plausibly enough, that evolution stands still (‘stasis’) for long periods punctuated by sudden rapid bursts called ‘speciation events’. They here invoked the theory of ‘allopatric speciation’.
Allopatric speciation means the splitting of a species into two by reason of an initial geographic separation – for example, on islands or on opposite sides of a river or mountain range. While separated, the two populations have the opportunity to evolve away from each
other so that, when they meet again in the fullness of time, they can no longer interbreed and are therefore defined as separate species. When a sub-population is separated from the mainland population on an offshore island, evolutionary change under island conditions can be so rapid that a new species arises almost instantaneously by the leisurely standards of geological time. An ‘island’, as discussed in ‘The giant tortoise’s tale’ (this page), doesn’t have to be land surrounded by water. For a fish, a lake is an island. For an Alpine marmot, a high peak is an island. For ease of illustration, I’ll continue to assume land surrounded by water.
When members of the island species migrate back to the mainland where the parent species is unchanged they will seem, to a paleontologist digging through the mainland rocks, to have arisen from the parent species in a single jump. The jump is an illusion. Gradual evolution really happened, albeit fast, and albeit offshore where the paleontologist isn’t digging. It’s easy to see that such ‘rapid gradualism’ is leagues away from true saltation. Yet Gould’s rhetoric contrived to mislead a generation of students and laypeople into confusion with true saltationism – even into confusion with mass extinction and the consequent ‘sudden’ rise of new evolutionary blossomings such as that of the mammals after the death of the dinosaurs. This is an example of what I call ‘poetic science’ – a phrase I’ll return to in the Afterword to this essay.
*11 ‘Nature doesn’t jump.’ In Huxley’s time his readers (including Darwin, whom he was directly addressing in a letter when he used the phrase) would have been, however unwillingly (especially in Darwin’s case), schooled in Latin.
Stephen Gould himself was present at my Cambridge lecture. After it, he jumped up and mentioned saltationism as one of several historical alternatives to Darwinian selection. Did he really not understand the impossibility of explaining the complex illusion of design by saltation – leaping from the bottom to the top of Mount Improbable in a single bound? It seems hard to credit. Gould was deeply interested in, and knowledgeable about, history. He was historically correct in asserting that some scientists in the early twentieth century had espoused saltationism as (what they thought was) an alternative to gradualism. But he was scientifically – even logically – incorrect to say that saltationism could ever be a viable alternative to gradualism as an explanation for complex adaptation. In other words, the historical figures that he correctly cited were scientifically wrong; it was always obvious. It should have been obvious, even in their own time, that they were wrong; and Gould should have said so.
*12 Stebbins was an American botanist, revered as one of the founding fathers of the neo-Darwinian synthesis of the 1930s and 1940s.
*13 Nowadays I would hesitate to use these two terms, because they have been co-opted by creationists eager, as ever, to misuse scientific terms in order to deceive. Geneticists studying populations in the field are looking at micro-evolution. Paleontologists studying fossils through the ages are looking at macro-evolution. Macro-evolution is actually nothing more than what you get when micro-evolution goes on for a very long time. Creationists, with some inadvertent help from a few biologists who should have been on their guard, elevate the distinction to qualitative heights. They accept micro-evolution, such as the replacement of light-coloured peppered moths by dark mutants in the population. But they think macro-evolution is qualitatively, radically different. For a fuller treatment of the actual, and supposed, distinctions, see ‘The “Alabama Insert” ’ in section IV of this collection.
*14 The complexity that was inserted – seats, bulkheads, call buttons, tray tables etc. – was simply duplicated from the pre-stretched version of the plane. The biological parallel would be an increase in the number of vertebrae, with associated ribs, nerves, blood vessels etc., when a mutant snake has more segments than its parents. Such ‘Stretched DC-8’ evolutionary changes must have happened often, because, for example, different species of snake vary greatly in how many segments they have. Children must have been born with different whole numbers of segments from their parents, because you can’t have a snake with a fraction of a vertebra.
*15 Actually, we have an intermediate in the form of the beautiful okapi, a cousin of the giraffes with a neck of intermediate length. But set that on one side for the sake of the example.
*16 As I was later to argue in 1989 when I coined the phrase ‘evolution of evolvability’ (in Artificial Life, a volume edited by Christopher Langton). I suggested there that, although rare, certain key stages in evolution, such as the origin of segmented body plans, may have occurred as sudden saltations. The first segmented animal could easily have had two segments. It would not have had one and a half.
*17 Sewall Wright was the American member of the great triumvirate – the others were R. A. Fisher and J. B. S. Haldane – who founded population genetics and reconciled Darwinism with Mendelian genetics. Wright espoused random genetic drift in evolution. But he saw drift as a way in which, indirectly, adaptation might be improved. One of the problems with strong selection, as engineers know from their ‘hill-climbing’ algorithms, is getting trapped on local optima – hillocks within sight of an unreachable mountain. Wright’s version of random drift enables a lineage to drift down the slope of a hillock into the valley, whereupon selection can then take over and propel it up the slopes of a much larger mountain. For Wright, drift alternating with selection allows greater perfection of adaptation than selection on its own. An excellent and brilliant suggestion.
*18 The one-way flow from genotype to phenotype – from genes to bodies – becomes obvious when you contrast the effect of a gene mutation (bodies change in future generations) with a purely bodily ‘mutation’, such as when an animal loses a leg. The latter change does not go through to future generations. There is a one-way causal arrow from genes to body, which is not reversed. I am astonished that Gould, in his ‘book-keeping metaphor’, failed to see this. ‘Book-keeping’ profoundly and significantly misses the point.
*19 This suggestion was persuasively made by the Scottish chemist Graham Cairns-Smith. I expounded his theory in The Blind Watchmaker, not because I necessarily believed it but because he so clearly emphasized the fundamental importance of replication in the origin of life.
*20 In nervous systems the problem is what engineers call random ‘noise’. Some noise is added during any information transmission or amplification process. Because of the way neurones work, they are more susceptible to noise than, for example, telephone wires. Just as modern telephone systems have increasingly gone over to digital rather than analogue transmission, so neurones convey information by the temporal patterning of spikes rather than by the (analogue) height of the spikes. For a fuller discussion of analogue vs. digital, see the analogy with beacon fires and the Spanish Armada, in the essay entitled ‘Science and sensibility’ in section I of this collection (see this page).
An ecology of replicators*1
TODAY, NOTWITHSTANDING LOCAL school boards in various backwoods and boondocks of the United States, no educated person doubts the truth of evolution. Nor do they doubt the force of natural selection. Natural selection is not the only driver and guide of evolution. At least at the molecular level, random drift is also important; but selection is the only force capable of producing adaptation. When it comes to accounting for the stunning illusion of design in nature, there is no alternative to natural selection.*2 If a biologist denies the importance of natural selection in evolution, it is pretty safe to assume not that he has some alternative theory but that he simply underrates adaptation as a dominant property of life that needs explaining. Probably he has never set foot in a tropical rainforest, or set flipper over a coral reef, or set eyes on a David Attenborough film.
Nowadays, questions about adaptation are high in the consciousness of field biologists. It has not always been so. My old maestro Niko Tinbergen wrote of an experience when he was a young man: ‘I still remember how perplexed I was upon being told off firmly by one of my zoology professors when I brou
ght up the question of survival value after he had asked: “Has anyone an idea why so many birds flock more densely when they are attacked by a bird of prey?” ’ Today’s student is more likely to be perplexed about what the professor could possibly have meant by his question if not survival value. People in Tinbergen’s own field of ethology now complain of a stampeding backlash in the other direction, towards an overwhelming preoccupation with Darwinian survival value, at the expense of studies of behavioural mechanisms.
But still when I was learning biology at school, we were warned against a dire sin called ‘teleology’. This was actually a warning against Aristotelian final causes, not against Darwinian survival value. Nevertheless, it perplexed me because I had never found final causes the slightest bit tempting. Any fool can see that a ‘final cause’ is not a cause at all.*3 It is just another name for the problem which, eventually, Darwin solved. Darwin showed how the illusion of a final cause could be produced by comprehensible efficient causes. His solution, refined by the giants of the modern synthesis including Ernst Mayr, has put paid to biology’s deepest mystery: the source of the illusion of design which pervades the living, but not the non-living world.
The illusion of design is at its strongest in the body shapes and behaviour patterns, the tissues and organs, the cells and molecules of individual creatures. The individuals of every species, without exception, show it powerfully. But there is another illusion of design which we notice at a higher level: the level of ecology. Design seems to reappear in the disposition of species themselves, in their arrangement into communities and ecosystems, in the dovetailing of species with species in the habitats which they share. There is a pattern in the intricate jigsaw of rainforest, say, or coral reef, which leads rhetoricians to preach disaster if but one component should be untimely ripp’d from the whole.
Science in the Soul Page 16
