Science of Discworld III

we’veseen, found his reason in Malthus’s contention that the unchecked growth of organisms is exponential, whereas that of resources is linear. In the long run, exponential growth always wins.
    The first assertion is pretty much correct, the second highly debatable. The qualifier ‘unchecked’ is crucial, and real populations only grow exponentially if there are plenty of resources available. Typically, the growth starts exponentially with a small population and then levels off as the population size increases. But in most species, two parents (let’s think sexual species here) produce some larger number of offspring. A breeding female starling lays about 16 eggs in her life, and with ‘unchecked’ growth, the starling population would multiply by 8 every lifetime. It would not be long before the planet was knee-deep in starlings. So, of necessity, 14 of those 16 offspring (on average) fail to breed – usually because something eats them. Just two become parents in their turn. A female frog may lay 10,000 eggs in her life, and nearly all die in various grotesque ways to achieve each two parents; a female cod contributes forty million or thereabouts of her offspring to planktonic food chains, for each two that breed. Here the multiplier, with ‘unchecked’ growth, would be 20 million per cod-lifetime. Unchecked growth simply doesn’t bear thinking about as a realistic prospect.
    We suspect that Malthus plumped for linear growth of resources for a slightly silly reason. Victorian school-textbook mathematics distinguished two main types of sequence: geometric (exponential) and arithmetic (linear). There were plenty of other possibilities, but they didn’t get into the textbooks. Having already assigned geometric growth to organisms, Malthus was left with arithmetic growth for resources. His main point doesn’t depend on the actual growth rate, in any case, as long as it is less than exponential. As the starling example shows, most offspring die before breeding, and that’s the main point here.
    Given that most young starlings cannot possibly become parents, the question arises: which ones will? Darwin felt that the ones thatsurvived to breed would be the ones best suited for survival, which makes sense. If one starling is better at finding food, or hanging on to it, than another one, then it’s clear which one is more likely to do best if food supplies become limited. The better one might be unlucky and get eaten by a hawk; but across the population, starlings that are better equipped to survive are generally the ones that do survive.
    This process of ‘natural selection’ in effect plays the role of an external breeder. It chooses certain organisms and eliminates the rest. The choice is not conscious – there is no consciousness to do the choosing, and no preconceived purpose – but the end result is very similar. The main difference is that natural selection makes sensible choices, whereas human selection can make ridiculous ones (like dogs with faces so flattened they can hardly breathe). Sensible choices lead to sensible animals and plants, ones that are beautifully adapted for survival in whatever environment they happened to be in when natural selection was moulding them.
    It is just like breeding new varieties of pigeon, but without a human breeder. Natural selection exploits the same variability of organisms that pigeon-breeding does. It makes choices based on survival value (in some environment) rather than whim. It is typically much slower than human intervention, but the timescale is so vast that this slowness doesn’t matter much. Heritable variation plus natural selection inevitably lead, over Deep Time, to the origination of species.
    Nature does it all on her own. There is no need for a series of acts of special creation. That doesn’t imply that special creation has not occurred. It just removes any logical imperative for it.
    Paley was wrong.
    The watches don’t need a watchmaker.
    They can make themselves.
    1 Literally, ‘jointed acorn’
    2 Yes, we know it sounds unlikely, but apparently there are such things.
    3 It was a good job that God had such a fondness for beetles.
    4 Its potential for Librarianship was not widely recognised at that time.
    5 No, not long-haired South American beasts of burden, but Latin for ‘gaps’.
    6 The term was around in Victorian times, as a phenomenon but not a specific mechanism. Darwin didn’t use it in Origin , nor in the later The Descent