The Science of Discworld IV

barbed bony supports in their dorsal and pectoral fins. In aquaria, these characteristics give them an entirely different ability, which we saw a plec exploiting in the Mathematics Institute common room at the University of Warwick. This plec’s natural abilities made it much better than other fish at garnering floating pellets of food. It did this using a method quite alien to wild plecs: it turned on its back and used its sucker-mouth to take in soggy pellets, while its spiky fins kept off the competition. So a catfish mouth, adapted for taking food from rocks, can be exapted to take food pellets from the water surface, especially if the fish concerned has effective defences, and the food is soft.
    Future genetic assimilation could easily build this kind of exapted behaviour into the genes of the plec population. It could be selected for, and then adapted along an evolutionary trajectory, so that a plec would take food from the surface
normally
in just this way.
    In fact, something of the kind has probably happened already – though not in descendants of the Mathematics Institute plec, which had none. The fish in question is the upside-down catfish
Synodontis nigriventris
, fn7 which takes insects from the surface of the water in the wild using a similar technique. We have, then, both ends of a plausible evolutionary trajectory. It starts, perhaps, with a hungry catfish alerted to a food mass on the surface, near it in shallow water; perhaps a rotting, floating insect carcass. The catfish turns over in its attempts to get its mouth near to the tempting morsel, and even if it mostly makes a hash of this, any occasional success is rewarded. It will now be sensitised to this source of food, and might haunt the shallows for more of them. Its offspring, growing up in the same environment, are then more likely to be selected for similar behaviour if genetic changes can make it more effective.
    This scenario contradicts Stephen Jay Gould’s assertion in
The Flamingo’s Smile
that adaptations like the upside-down feeding of the flamingo, scooping up crustaceans from saline lakes, must involve a single radical departure from the normal use of the beak. Animals can try out little behavioural experiments, and if they are rewarded, these can become built into their subsequent behaviour. Then, if the reward is as important as a new source of food or novel access to mates, natural selection can improve it.
    Technical evolution can avoid such time-wasting, progeny-wasting, and new-function-wasting aspects of organic evolution in two ways. The first, we have discussed already: human minds can attempt tojump into the adjacent possible and see if it works ‘in the imagination’. Can we imagine an aeroplane ten times the size, and what would need to be changed for it to work? If we exaggerated the length of a bicycle frame and had the cyclist lean back, how could he see the road? Do we then want him on his front? Both have been tried, and are excellent examples: technical results of our imagination playing in the adjacent possible.
    The other trick that minds can do to improve technology is to copy: to take a technical trick used in one invention and to spread its use to others. That trick, except for a few cases where genes have achieved horizontal transfer between species, is impossible for organic evolution: each lineage must invent for itself. A recent spread of this kind has been the use of digital switches in a variety of machines from toasters and children’s toys to automobiles. The big one before that was the use of plastics to replace metals in the nursery, kitchen and laboratory. Before that, transparent plastics, mostly acrylics, had been used to replace glass in many applications. The progressive use of semiconductor technology is giving us solar panels, tiny refrigerating or heating elements, and a new family of very efficient light bulbs: white-light LEDs. Banks of coloured LEDs can now be tuned to give different lighting conditions; bright white light is not conducive to sleep and can be replaced with softer tones. Flexible television/computer screens, which can be rolled up like paper, already exist in the laboratory, and are not far from commercial production. An entire book has just been encoded in DNA, and a human face has been printed on a human hair.
    In biological evolution, it used to be thought that environmental ‘niches’, such as predatory behaviour, were already available and waiting to be