The Science of Discworld IV Judgement Da - By Terry Pratchett, Ian Stewart Page 0,82
di- and tri-phosphate). Indeed, ATP is often called the unit of molecular currency. The appearance of new designs in organic evolution, in cultures, in technology, and even in language, can usefully be compared. Even so, such comparisons must be made very carefully and not pushed beyond reasonable limits.
The idea that technology evolves is not the orthodox view, wherein design and evolution are considered to be opposites. Design in technology is usually seen as being invented, not as having evolved. This assumption lies at the core of Paley’s famous analogy between a living creature and a watch. Watches are intricate devices, designed and made by an intelligent agency. Therefore, if you find something equally intricate in living creatures, it must also be designed, and the creatures must have been made by an intelligent agency. Therefore there must have been a cosmic designer, QED. The same assumption motivates the current hypothesis of intelligent design, which is basically Paley’s argument restated using examples from modern biochemistry.
However, analysis of the history of nearly all inventions shows them either to be developments of previous technology, that is to say adaptations, or perversions of some technology in a different sphere. (A few do seem to come out of thin air, with no significant precursors.) The biological term for such things is ‘exaptations’, a word introduced by Gould and Elizabet Vrba in the 1980s. It refers to an organic or a technological development that arises from an entirely different structure or function. An example is the use of feathers for flight. Feathers first appeared in dinosaurs, but their skeletal structure shows that the early feathered dinosaurs didn’t use their feathers to fly. We can’t be certain what they did use them for, but the most plausible functions are for warmth or for sexual display. It may well have been both. Later, feathers turned out to be useful for wings and flight, and birds evolved. Nature is an opportunist. A technological example of exaptation is the use of disc-recorded sound for music. Edison originally developed the phonograph for a more serious purpose, to record for posterity the last words of famous men and the historical speeches of politicians. He greatly deplored its use for frivolities like music, but accepted payments gracefully, nevertheless.
Exaptation is one of the less obvious tricks that evolution has up its sleeve, and is often the solution to evolutionary puzzles, in which a particular function can occur only when several interrelated structures apparently have to appear simultaneously, but none of them can perform that function on its own. Although it’s tempting to deduce that such structures can’t evolve at all, they can if exaptations occur. Then the structures concerned initially perform different functions.
A classic instance is the bacterial flagellum, a structure that proponents of intelligent design argue cannot possibly have evolved by any conceivable route. The flagellum allows some bacteria to move of their own volition. Its most important component is a tiny molecular motor, which causes the flagellum to rotate, much as the motor of a boat turns the propeller. The bacterial motorfn5 is made from a large number of different protein molecules. Until recently, evolutionary biologists could offer no convincing explanation of the origin of such a complex structure by natural selection.
In 1978 Robert MacNab wrote: ‘One can only marvel at the intricacy, in a simple bacterium, of the total motor and sensory system … What advantage could derive … from a “preflagellum” [meaning a subset of its components], and yet what is the probability of “simultaneous” development?’ In 1996 Michael Behe, a biochemist and leading proponent of intelligent design, repeated MacNab’s worries in Darwin’s Black Box, together with several similar evolutionary puzzles. He concluded that while many, indeed most, features of living creatures have evolved, some cannot possibly have done so because they are irreducibly complex: if you remove any component, they cease to function.
It’s a genuine puzzle, but before invoking some unspecified genie-of-the-lamp, without independent evidence that it exists, we ought to make sure that conventional evolutionary processes definitely can’t hack it. Intelligent design doesn’t just argue that some specific evolutionary route is wrong: it claims a proof that in principle no such route can exist. If you’re going to invoke a general principle of this kind to assert the existence of a supernatural being or a highly advanced cosmic designer, you need to close any loopholes in your logic. Otherwise your entire philosophy will be built on sand, whatever actually happened. The Book of Genesis could be true in every