William Paley, an 18th century English clergyman and Christian apologist, is particularly remembered today for his development of the classic argument for the existence of God known as the Argument from Design. In the Middle Ages, this was merely one of a number of inductive arguments that were used to establish that it was more reasonable to believe in God than to disbelieve in him. Although these classic arguments are often referred to as “proofs” of God’s existence, they are not proofs in the strict sense because they depend on induction and not deduction and therefore can be challenged or rejected. They all start with a generally agreed feature of the universe and suggest that creation by God is the most reasonable explanation of why this feature exists (although there could in principle be other explanations).
Some of these arguments are actually pre-Christian and look rather unconvincing today. For example Aristotle, accustomed to the rocky roads of Greece, argued that nothing can move unless it is put into motion by something else. A cart will move only if it is drawn by horses. This leads naturally to the idea that nothing in the universe could move at all unless there was an original Prime Mover to get the whole process started. Catholic theologians had come to revere Aristotle, whose works they first read in Arabic translations, and were inclined to believe whatever he said. So they happily adopted his Prime Mover and identified it as God. And later on, as Nicholas Spencer has pointed out in his book Magisteria, Galileo got into trouble with the Church not because his heliocentric astronomy challenged the Bible (actually the Bible has nothing to say about the matter directly) but because it challenged Aristotle.
In the Catholic Church, the traditional “proofs”, including the Aristotelian one, continued to be taught as a set, but this was not the case in Protestant countries. In England in particular, there was a great flowering of what we would nowadays call natural history which was entirely centred on the Argument from Design. Gentleman scientists, who were often clergymen, studied the structures of animal and plant bodies in detail and marvelled over their perfect adaptation to the requirements of their lifestyle. Far from science and religion being at odds, they appeared in England to run happily in a double harness with nature taking its place as God’s Second Bible.
This found its perfect expression in Paley’s parable of the watch, which so captivated the English public that it made the Argument from Design almost the only theistic argument worth making. Paley imagined a man walking along a beach and finding a pocket watch, perhaps flotsam from a shipwreck. He opens it and marvels at the intricate arrangement of gear wheels inside. Even if he belongs to a primitive race who have not yet invented the wheel, he will know at once that this is not the product of random forces but a designed object, the work of an intelligent being. In the same way, Paley argued, the perfect adaptation of myriads of living beings to their environment was proof that the entire biosphere had been designed by an intelligent God.
The increasing dependence of Christian preachers and evangelists on this single argument partly explains why Darwin’s theory of evolution by natural selection had such a devastating effect. It was not, contrary to a popular modern belief, because of perceived clashes with the Book of Genesis. These could easily be explained away as the difference between scientific description and poetic symbolism. It was much more because the Church had become psychologically dependent on Paley’s Watch argument, and natural selection now provided an alternative non-theistic explanation for the exquisite adaptation of living things to their environment and to one another.
Nowadays, Paley’s Watch is usually mentioned by evolutionary biologists only in passing and with an implied sneer. But it seems to me that reviving the metaphor might be the key to solving one of the great riddles of evolution: how life itself evolved. The mechanisms of Darwinian evolution, the interplay of genetic variation and environmental pressure, imply the existence of a genetic code implemented in DNA or something functionally equivalent. And that requires a complete enzymatic system for generating and copying DNA and transcribing it into proteins whose function can be tested by the environment. But where did all this come from? There seems on the face of it to be no way to get directly from non-living organic matter to life as we know it.
Inevitably fundamentalists have seized on this as proof that only a miracle could have bridged the gap between non-life and life and therefore a miracle-working God must exist. I find this a very unattractive argument for religious as well as scientific reasons. The word “miracle” comes from the Latin mirare, which means to wonder or marvel. A miracle is therefore an event whose purpose is to evoke wonder and demonstrate the greatness of God. The underlying Hebrew word in the Bible is “sign” as in “signs and wonders”. The miracles worked by Jesus are presented as signs of His divinity. A miracle which has no purpose but to bridge a functional gap in creation is more likely to evoke irritation than wonder in the scientific observer. It suggests an incompetent god rather than a superintelligent one. Surely if God creates a planet which is designed to bring forth life, it will actually do so and not require this kind of divine tinkering at the edges.
So, as we cannot get directly from non-life to life without a most inappropriate miracle, we shall need to postulate a continuous range of intermediate states that we might call proto-life. This proto-life continuum will shade at one end into non-life, mere biochemistry, and at the other end into life — perhaps not life as we currently know it but surely something like an early version of that. So what would the graded realm of proto-life actually look like? Surprisingly it would look rather like an early workshop version of Paley’s Watch.
If you open a watch as Paley’s traveller does, what do you actually see? You see a number of toothed gear wheels that interlock with each other. There is a main wheel which is slowly turned by a gradually relaxing spring, and this turns all the other wheels directly or indirectly. The rotational speed of each wheel is determined by the ratio of its diameter to the diameter of the wheel that turns it. If it is half the size of its driver, it will turn at twice the rate. The final end-points are a wheel that moves the hour hand over a period of twelve hours, another which turns the minute hand with a period of one hour, and probably a third wheel that turns a seconds hand over one minute.
Now look inside a living cell. You don’t see any obvious wheels but they are there all the same, cycles of metabolism that are invisible because they extend through time rather than space. A compound A will be converted into another compound B, which is converted into C, and so on and on until the final step in the cycle regenerates A. The Krebs respiratory cycle is a good example. At each rotation, one or more small molecules will be sucked in and one or more different small molecules will be spat out. If the output of one cycle serves as a necessary input for another, the two cycles will be locked together. And if the first cycle outputs two molecules of this substance per rotation, and the second requires only one such molecule to be input per rotation, then that second wheel will turn at twice the speed of the first, exactly as a wheel of half the diameter would do inside a watch.
What is the likelihood of such a thing occurring without miraculous intervention from outside? I think we need to distinguish here between two different kinds of improbability. There are a lot of events which are improbable only in the sense that they are exceedingly infrequent. They will not occur in a hundred years, maybe not in a thousand or ten thousand, but they are bound to occur eventually, given enough time. And there are other things which will never occur spontaneously, no matter how long you wait. Let us call these first-order and second-order improbabilities. Second-order improbabilities are effectively impossible and no amount of handwaving and shouting “Billions and billions of years!” will make them happen. A tornado barrelling through a junkyard will never spontaneously assemble a car. But first-order improbabilities are bound to happen eventually if you wait long enough, and successive ones can add up in a kind of ratchet effect.
The spontaneous appearance of a closed chemical cycle is only first-order improbable. It is somewhat unlikely that a chain of chemical reactions will catch its own tail and become a cycle, but it has been known to happen in completely abiotic environments. More importantly, a variety of different spontaneously generated chemical cycles have been found, and the kind of small molecules that such a cycle is liable to suck in or spit out are usually very common ones like methane or carbon monoxide. So it is also first-order improbable (and far from impossible) that two such cycles will interlock, especially if there is a local environment which concentrates organic chemicals and provides an energy source for their interaction. Two such environments have been postulated by different scientists as likely ones for the genesis of life: shallow pools that repeatedly evaporate and refill (Darwin’s preference), and the tubular pores in deep-sea alkaline stacks which are acidic at their mouths and strongly alkaline at their closed ends, providing a chemical gradient that can do work. Of course a further requirement is the absence of existing living things that would gobble up the newly formed organic chemicals!
Once two cycles do interlock in a specific place, the association will be permanent. It will then be rather easier for a third “chemical wheel” to lock on or even develop in-situ. By the same logic, adding extra wheels to the existing system should become easier still until eventually it is no longer even improbable because there are now so many potential “locking-on sites”. And so we move gradually from something that is intriguing but definitely not life through a series of states that are not life either but are becoming more and more lifelike to something of which one could say, “That really does look like a living system to me.”
Much that is characteristic of present day life would still have been absent, in particular the DNA-protein loop. Undoubtedly the first genetic coding material was RNA, which is single-stranded and can therefore coil itself into different shapes and act as a catalyst just as a protein might do. Somewhere along the way an RNA polymer appeared that could autocatalyse its own formation, then variants that could catalyse other useful reactions including the stringing together of amino acids to make the first peptide replacement catalysts. Some form of ribosome would be needed to create these, and there is indeed evidence that the oldest part of the modern ribosome is a simple dehydration catalyst that can link amino acids into chains. The part that reads three-letter RNA codes to pull in particular amino acids would have come later. Long-chain proteins, which are far better catalysts than peptides because they can assume a greater variety of shapes, would have come much later. And DNA, which is more stable than RNA but requires protein enzymes to process it, probably started out as a kind of backup tape rather than the primary genetic storage medium that it is now. There are still some viruses (notably covid) that don't use it. The final addition may have been the cell wall, since the two main branches of life, bacteria and archaea/eucaryotes, have different ones.
In principle, the sequence of events could be unpicked and perhaps even duplicated artificially in a speeded-up form. It would be amusing to vindicate Paley after all these decades by showing that God is indeed a watchmaker who used a system of interlocking rotating wheels to bridge the gap between the inanimate universe and life as we know it.
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