The Science of Discworld IV

motor, from DNA and other biochemical evidence. This turns out not to be especially difficult. Many details are still provisional, as is all science, but the story is now sufficiently complete to disprove the contention that the motor exhibits a type of complexity that rules out
all
evolutionary explanations. Agreed, that doesn’t prove that the current evolutionary explanation is correct. That must be confirmed, or denied, by further scientific investigations. But it’s quite different from asking whether, in principle, any such explanation can exist.
    The most fully developed synthesis of these proposals, put together by Nicholas Matzke, starts with a general-purpose pore. This evolves into a pore with more specific functions. At this early stage, the structure is not a motor, but it already has a very useful, entirely different, function: it can transport molecules out of the cell. In fact, it is recognisable as a primitive version of so-called Type III Export Apparatus, which exists in modern bacteria, and DNA sequences support this. Further changes, in which the pore’s function is successively improved, or changed by exaptation, provide an entirely plausible evolutionary route to the bacterial motor, increasingly supported by DNA evidence. fn6
    Yes, if you take away enough parts of the bacterial motor, then it might not be a very good motor any more. But evolution didn’t know it was supposed to be making a motor.
    So ‘design’ isn’t what it is often thought to be, even for human technology, let alone biology. Each innovative step may be driven by human intentions, but what works, and what passes on to later technology, evolves. To some extent, cars evolved from horse-drawn carriages, and a ballpoint pen is the lineal descendant of a quill made from a feather. We can legitimately compare these developments to mammals evolving from a Devonian fish that came out of the water onto land, or to our little middle-ear bones being the lineal descendants of bony gill structures in that fish.
    Evolution is not efficient. It throws an awful lot of things away. Innumerable land vertebrate species have gone extinct. Similarly, most human designs don’t work. From the enormous number on offer, only a few develop into sophisticated structure/function niches. We are all bound by tradition, as well as by functional constraints that require any new development to fulfil the same functions as its ancestor. There’s a classic example: Apollo rockets were moved to their launching-pads on rails that were much too close together for stability, because the gauge of America’s railways came from mine railways that were two horses wide. So the Moon project was jeopardised by horse’s asses.
    To be specific, let’s think about better mousetraps. Mousetrap evolution is a process, not just a succession of models; it branches into the future. The pattern that has a metal bar coming down and (one hopes) breaking the mouse’s neck, has expanded into dozens of different models, some computer-controlled. Those that trap the mouse in a metal tube, or a cage, are more like descendants of lobster-pots, but these too have performed what biologists would call an adaptive radiation: we found seven different kinds, with sprung doors or elastic apertures for entry.
    The same goes for bicycles, cars or computers: they all adaptively radiate into the future. Each new ability, such as computer control – a logic chip – on a particular technical road branches into new roads. Think of the familiar cat flap, now available in versions that allow your own cat, wearing its magnetic collar, in or out, but exclude foreign cats. Or fancy electronic ones that verify your cat’s ID. Full-body scanners to detect terrorist cats carrying exploding mice cannot be far away. Just as in organic evolution, the adjacent possible is continually being invaded: possibilities just one step away from current practice are tried, rather unoriginally.
    We usually think of this as technical development, not innovation, unless it is in an unexpected direction: Teflon used for non-stick frying-pans, or penguins’ wings used for swimming. Most aquatic vertebrates, unlike these birds that have become secondarily aquatic, use their tails, not their fins, for propulsion. Such more original changes of direction are best thought of as exaptations rather than adaptations. Or, to use a less biological term, genuine innovations.
    Among those who accept evolution as a