Darwin's Watch Page 5

  The evolutionary competitions, and their outcomes, also depend on context. Climate, in particular, plays a big role. In the Galapagos, selection for beak size in Darwin's finches depends on how many birds have what size of beak, and on what kinds of food - seeds, insects, cactus - are available and in what quantities. The amount and type of food depend on which plants and insects are competing best in the struggle to survive - not least from being eaten by

  finches - and breed. And all of this is played out against a background of climatic variations: wet or dry summers, wet or dry winters. Observations published in 2002 by Peter and Rosemary Grant show that the main unpredictable feature of finch evolution in the Galapagos is climate. If we could forecast the climate accurately, we could predict how the finches would evolve. But we can't predict the climate well enough, and there are reasons to think that this may never be possible.

  That doesn't prevent evolution from being `predictive', hence a science, any more than it prevents meteorology from being a science. But the evolutionary predictions are contingent upon the behaviour of the climate. They predict what will happen in what circumstances, not when it will happen.

  Darwin almost certainly read Paley's masterwork as a young man, and in later life he may well have used it as a touchstone for his own, more radical and far more indirect, views. Paley succinctly expressed many of the most effective objections to Darwin's ideas, long before Darwin arrived at them. Intellectual honesty demanded that Darwin should find convincing answers to Paley. Such answers are scattered throughout Darwin's epic treatise The Origin of Species, though Paley's name does not appear.

  In particular, Darwin found it necessary to tackle the thorny question of the eye. His answer was that although the human eye appears to be a perfected mechanism, with many interdependent parts, there are plenty of different `eyes' in the animal kingdom, and a lot of those are relatively rudimentary. They can even be arranged in a rough progression from simple light-sensing patches to pinhole cameras to complex lenses (though this arrangement should not be interpreted as an actual evolutionary sequence). Instead of half an eye, we find an eye that is half as effective at detecting light. And this is far, far better than no eye at all.

  Darwin's approach to the eye is complemented by some computer experiments published by Daniel Nilsson and Suzanne Pelger [1] in 1994. They studied a simple model of the evolution of a lightsensing patch of cells, whose geometry could change slightly at every `generation', and which was equipped with the capacity to develop accessories such as a lens. In their simulations, a mere 100,000 generations were enough to transform a light-sensing patch into something approaching the human eye, including a lens whose refractive index varied from place to place, to improve its focus. The human eye possesses just such a lens. Moreover, and crucially, at every one of those 100,000 steps, the eye's ability to sense light got better.

  This simulation was recently criticised on the grounds that it gets out what it puts in. It doesn't explain how those light-sensing cells can appear to begin with, or how the eye's geometry can change. And it uses a rather simplistic measure of the eye's performance. These would be important criticisms if the model were being used as some kind of proof that eyes must evolve, and as an accurate description of how they did it. However, that was never the purpose of the simulation. It had two main aims. One was to show that in the simplified context of the model, evolution constrained by natural selection could make incremental improvements and get to something resembling a real eye. It wouldn't get stuck along the way with some dead-end version of the eye that could be improved only by scrapping it and starting afresh. The second aim was to estimate the time required for such a process to take place (look at the title of the paper), on the assumption that the necessary ingredients were available.

  Some of the model's assumptions are easily justified, as it happens. Light carries energy and energy affects chemical bonds, so it is not

  [1] 'A pessimistic estimate of the time required for an eye to evolve', Proceedings of the Royal Society of London B, volume 256 (1994), pp. 53-8.

  surprising that many chemicals respond to light. Evolution has an immense range of molecules to draw on - proteins specified by DNA sequences in genes. The combinatorial possibilities here are truly vast: the universe is not big enough, and has not lasted long enough, to make one molecule of each possible protein as complex as, say, haemoglobin, the oxygen-carrier in blood. It would be utterly astonishing if evolution could not come up with at least one light-sensing pigment, and incorporate it into a cell.

  There are even some ideas of how this may have happened. In Debating Design, Bruce Weber and David Depew point out that lightsensitive enzyme systems can be found in bacteria, and these systems are probably very ancient. The bacteria don't use them for vision, but as part of their metabolic (energy-gaining) processes. Proteins in the human lens are very similar to metabolic enzymes found in the liver. So the proteins that make the eye did not start out as components of a system whose purpose was vision. They arose elsewhere and had quite different `functions'. Their form and function were then selectively modified when their rudimentary light-sensing powers turned out to offer an evolutionary advantage.

  Although we now know quite a lot about the genetics of the human eye, no biologist claims to know exactly how it evolved. The fossil record is poor, and humanoid eyes don't fossilise (though trilobite eyes do). But biologists can offer simple reasons why and how the eye could have evolved, and these alone are sufficient to demolish claims that its evolution is impossible in principle because the eye's components are interdependent and removing any one of them causes the eye to malfunction. The eye did not evolve one component at a time. Its structure evolved in parallel.

  The instigators of more recent revivals of Paley's doctrine, albeit in less overtly theist tones, have taken on board the message of the eye as a specific case ... but its more generic aspects seem to have

  eluded them. Darwin's discussion of the eye, and the Nilsson-Pelger computer experiment, are not limited to eyes. Here is the deeper message. When confronted with a complex living `mechanism', do not assume that the only way it can evolve is component by component, piece by piece. When you see a watch, do not think of hooking up springs and adding cogwheels from some standard box of spare parts. Think more of a Salvador Dali `soft watch' that can flow and distort, deform, split apart, and rejoin. Think of a watch whose cogwheels can change shape, grow new teeth, and whose axles and supports evolve along with the cogs so that at every stage the whole thing fits together. Think of a watch that may have started out as a paper clip, and along the way became a pogo-stick. Think not of a watch that does and always did have a single purpose, which was to tell the time. Think of a watch that once held sheets of paper together and could also be straightened out to form a toothpick, and which later turned out to be great for bouncing, and started to be used for measuring time only when someone noticed that its rhythmic movements could chart the passing seconds.

  Yes, proponents of intelligent design understand the eye ... but only as one example, not as the basis of a general principle. `Oh, yes, we know all about the eye,' they say (we paraphrase). `We're not going to ask what use half an eye is. That's simple-minded nonsense.' So instead, they ask what use half a bacterial flagellum is, and thereby repeat the identical error in a different context.

  We owe this example to Michael Behe, a biochemist who was baffled by the complexity of bacterial flagella. These are the `tails' that bacteria use to move around, tiny `screws' like a ship's propeller, driven by a rotary molecular motor. Some forty proteins are involved in making such a motor, and if you miss any of them out, it won't work. In his 1996 Darwin's Black Box, Behe claimed that the only possible way to make a flagellum was to encode the whole structure, in advance, in bacterial DNA. This code could not have evolved from anything simpler, because the flagellum is `irreducibly complex'.

  An organ or biochemical system is said to be irreducibly complex if removing any of
its parts causes it to fail. Behe deduced that no irreducibly complex system can evolve. The example of the bacterial flagellum quickly became a cornerstone of the intelligent design movement, and Behe's principle of irreducible complexity was promoted as an unavoidable barrier to the evolution of complex structures and functions.

  There are several excellent books that debate intelligent design: we've mentioned two earlier in a footnote. It's fair to say that the antis are winning the debate hands down - even in books edited by the pros, such as Debating Design. Perhaps the biggest problem for the pros is that Behe's fundamental concept of `irreducible complexity' has fatal flaws. With his definition, the deduction that an irreducibly complex system cannot evolve is valid only if evolution always consists of adding new parts. If that were the case, then the logic is clear. Suppose we have an irreducibly complex system, and suppose that there is an evolutionary route leading to it. Focus on the final step, where the last part is added. Then whatever came before must have been a failure, so it couldn't have existed. This is absurd: end of story.

  However, evolution need not merely add identifiable components, like a factory-worker assembling a machine. It can also remove them - like a builder using scaffolding and then taking it down once it's done its job. Or the entire structure can evolve in parallel. Either possibility allows an irreducibly complex system to evolve, because the next to last step no longer has to start from a system that lacks that final, vital piece. Instead, it can start from a system with an extra piece, and remove it. Or add two vital pieces simultaneously. Nothing in Behe's definition of irreducible complexity prohibits either of these.

  Moreover, `fail' is a slippery concept: a watch that lacks hands is a failure at telling the time, but you can still use it to detonate a timebomb, or hang it on a string to make a plumb-line. Organs and biochemical systems often change their functions as they evolve, as we've just seen in the context of the eye. No satisfactory definition

  of `irreducible complexity' - one that really does constitute a barrier to evolution - has yet been suggested.

  According to Kenneth Miller in Debating Design: `the great irony of the flagellum's increasing acceptance as an icon of the antievolutionist movement is the fact that research had demolished its status as an example of irreducible complexity almost at the very moment it was first proclaimed'. Removing parts from the flagellum do not cause it to `fail'. The base of the bacterial motor is remarkably similar to a system that bacteria use to attack other bacteria, the `type III secretory system'. So here we have the basis of an entirely sensible and plausible evolutionary route to the flagellum, in which protein components do get added on. When you remove them again, you don't get a working flagellum - but you do get a working secretory system. The bacterial method of propulsion may well have evolved from an attack mechanism.

  To their credit, proponents of intelligent design are encouraging this kind of debate, but they have not yet conceded defeat, even though their entire programme rests on shaky foundations and is collapsing in ruins. Creationists, desperate to snatch at any straw of scientific respectability for their political programme to lever religion into the American state school system, [1] have not yet noticed that what they are currently taking as their scientific support is falling apart at the seams. The theory of intelligent design itself is not overtly theist - indeed its proponents try very hard not to draw religious conclusions. They want the scientific arguments to be considered as science. Of course that's not going to happen, because the theist implications are a little too obvious - even to atheists.

  There are some things that evolution does not explain - which will gladden the heart of anyone who feels that, Darwin notwithstanding, there are some issues that science cannot address.

  [1] ' They themselves refer to this programme as the 'wedge strategy'.

  It is perfectly possible to agree with Darwin and his successors that the Earth is 4.5 billion years old, and that life has evolved, by purely physical and chemical processes, from inorganic beginnings - yet still find a place for a deity. Yes, in a rich and complex universe, all these things can happen without divine intervention. But ... how did that rich and complex universe come into being?

  Here, today's cosmology offers descriptions of how (Big Bang, various recent alternatives) and when (about 13 billion years ago), but not why. String theory, a recent innovation at the frontiers of physics, makes an interesting attempt at `why?' However, it leaves an even bigger `why?' unanswered: why string theory? Science develops the consequences of physical rules (`laws'), but it doesn't explain why those rules apply, or how such a set-up came to exist.

  These are deep mysteries. At the moment, and probably for ever, they are not accessible to the scientific method. Here religions come into their own, offering answers to riddles about which science chooses to remain mute.

  If you want answers, they are available.

  Rather a lot of different ones, in fact. Choose whichever one makes you feel most comfortable.

  Feeling comfortable, however, is not a criterion recognised by science. It may make us feel warm and fuzzy, but the historical development of scientific understanding shows that, time and again, warm and fuzzy is just a polite way of saying `wrong'.

  Belief systems rely on faith, not evidence. They provide answers - but they don't provide any rational process to assess those answers. So although there are questions beyond the capacity of science to answer, that's mostly because science sets itself high standards for evidence, and holds its tongue when there isn't any. The alleged superiority of belief systems compared to science, when it comes to these deep mysteries, stems not from a failure of science, but from the willingness.of belief systems to accept authority without question.

  So the religious person can take comfort that his or her beliefs provide answers to deep questions of human existence that are beyond the powers of science, and the atheist can take comfort that there is absolutely no reason to expect those answers to be right. But also no way to prove them wrong, so why don't we just coexist peacefully, stay off each other's turf, and each get on with our own thing? Which is easy to say but harder to do, especially when some people refuse to stick to their own turf, and use political means, or violence, to promote their views, when rational debate long ago demolished them.

  Some aspects of some belief systems are testable, of course - the Grand Canyon is not evidence for Noah's flood, unless God is having a quiet joke at our expense, which admittedly would be a very Discworld thing to do. And if He is, then all bets are off, because His revealed word in [insert your preferred Holy Book] may well be a joke too. Other aspects are not testable: the deeper issues stray into intellectual territory where, in the end, you have to settle for whatever explanation your type of mind finds convincing, or just stop asking that kind of question.

  But remember: what's most interesting about your beliefs, to anyone who does not share them, is not whether you're right - it's that what you believe is a window into the workings of your mind. `Ah, so you think like that, do you?'

  This is where the great mystery of human existence leads, and where all explanations are true - for a given value of `true'.

  FIVE

  THE WRONG TROUSERS OF TIME

  THE GLASS GLOBE OF ROUNDWORLD had been installed

  on a pedestal in front of Hex by the time most of the senior faculty were up and milling around. They were always at a bit of a loose end when Second Breakfast

  had finished and it wasn't yet time for Elevenses, and this looked like entertainment.

  `One asks oneself whether it really is worth saving,' said the Chair of Indefinite Studies. `It's had huge ice ages before, hasn't it? If the humans are too stupid to leave in time, then there's bound to be another interesting species around in half a million years or so.'

  `But extinction is so ... sort of . . . final,' said the Lecturer in Recent Runes.

  `Yes, and we created their world and helped them become intelligent,' said the Dean. `We can't just let
them freeze to death. It'd be like going on holiday and not feeding the hamster.'

  A watchmaker as part of the watch, thought Ponder, adjusting the university's biggest omniscope; not just making the world, but tweaking it all the time ...

  Wizards did not believe in gods. They didn't deny their existence, of course. They just didn't believe. It was nothing personal; they weren't actually rude about it. Gods were a visible part of the

  narrativium that made things work, that gave the world its purpose. It was just that they were best avoided close up.

  Roundworld had no gods that the wizards had been able to find. But one that was built in ... that was a new idea. A god inside every flower and stone ... not just a god who was everywhere, but a god who was everywhere.

  The last chapter of Theology of Species had been very impressive ...

  He stood back. Hex had been busy all morning. So had the Librarian. Right now he was carefully dusting books and feeding them into Hex's hopper. Hex had mastered the secret of osmotic reading, normally only ever attempted by students.

  And the Librarian had located a copy of the right Origin of Species, the book Darwin ought to have written. It had a picture of Darwin as a frontispiece. With a pointy hat he would have passed for a wizard anywhere. If it came to that, he could have passed for the Archchancellor.