The Science of Discworld IV

reasonable metaphor for many examples of progress in technology, it used to be thought that the major difference between technical and organic evolution is that technological evolution is Lamarckian – named after the French naturalist Jean-Baptiste Lamarck, a contemporary of Darwin – whereas organic evolution is Darwinian. In Lamarckian evolution, acquired characteristics can be inherited – if a blacksmith acquires strong arms because of his work, his sons should also have strong arms. In Darwinian evolution, that’s not possible. Neo-Darwinism illuminates the difference: heritable characteristics are those that are determined by genes.
    Lately, this distinction has become a bit blurred, and each mechanism has acquired features that were thought to be characteristic of the other. Technical development has borrowed a trick from evolution to construct so-called genetic algorithms for the developmentof new products. Digitised designs are shuffled, by analogy with recombination, the way biological reproduction shuffles gene variants from both parents. The next technological generation to survive this process combines the more useful features of previous generations. Sometimes it has new emergent properties, which are selected if they prove useful, and are retained. Often the final design is incomprehensible to a human engineer. Evolution need not obey human narrativium.
    The phenomenon of genetic assimilation, which is entirely Darwinian, can look very Lamarckian. Changing a population progressively by selecting genetic combinations that work can change the thresholds at which particular capabilities come into play. As a result, effects that originally depended on some environmental stimulus can happen without that stimulus in later generations. For example, the skin on the soles of our feet gets thicker when we walk regularly, an acquired characteristic; however, genetic recombinations that provide babies with thicker skin on their feet from the start make this process more effective, and so are selected for. Any new feature, acquired or not, that
works
– that improves the chances of surviving to reproduce – reveals a feature that Darwinian evolution could blunder into and exploit. Genetic assimilation may indeed be the usual way that originally responsive adaptations get built in to the developmental schedule.
    In particular, the old distinction between Lamarck and Darwin has lost its power to distinguish technical from organic evolution. But that doesn’t imply that there are no significant differences. It’s tempting to think that one obvious aspect of technological evolution surely can’t apply to Darwinian evolution:
imagining
a possibility before designing a technique or gadget to implement it. Human technology is born in the imagination of a series of inventors or discoverers: ‘What would happen if …?’ is a theoretical exploration of Kauffman’s adjacent possible. Much of the time, imagining possibilities leads to hypothetical new inventions being rejected withoutbothering to make them or test them: they wouldn’t work because …
or
no one could use them because …
or
they would be too expensive …
or
they wouldn’t perform well enough to displace the widget that already does the job very well.
    It doesn’t seem possible that this imaginative process could have an organic analogue – but it does. In 1896 the psychologist James Mark Baldwin wondered whether animals carrying out behavioural experiments might be drawn into the evolutionary process, in effect by imagining what would happen if they could perform some new task that was actually beyond them. For instance, an okapi is like a giraffe, but its neck and legs are of normal length. Suppose that an adventurous okapi, for example, kept reaching up in an attempt to browse on the lowest branches of trees, despite repeated failure.
Because
it failed, this would be analogous to imagination. But occasional success could favour okapi with slightly longer necks and legs, leading to a giraffe. This process is often called the Baldwin effect.
    A few years ago, we observed some animal behaviour that could well become the root of such an evolutionary trajectory – an exaptation in the making. Plecostomid catfish (‘plecs’) are common scavengers in larger aquariums, cleaning algae off the glass with their sucker-like mouths. In the wild, they can hold tight to smooth rocks as they glean the algal film; they also have effective armour with