Science of Discworld III

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 time-bomb, 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 definitionof ‘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 anti-evolutionist 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, 5 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.
    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