That seems absurd today, because the actual molecular mechanisms of life are now known. But is there anything wrong with that theory itself, as an explanation? Phenomena such as rainbows have a distinctive appearance that is endlessly repeated without any information having been transmitted from one instance to the next. Crystals even behave in ways that are reminiscent of living things: when placed in a suitable solution, a crystal attracts more molecules of the right kind and arranges them in such a way as to make more of the same crystal. Since crystals and mice both obey the same laws of physics, why is spontaneous generation a good explanation of the former and not of the latter? The answer, ironically, comes from an argument that was originally intended to justify creationism:
The argument from design
The ‘argument from design’ has been used for millennia as one of the classic ‘proofs’ of the existence of God, as follows. Some aspects of the world appear to have been designed, but they were not designed by humans; since ‘design requires a designer’, there must therefore be a God. As I said, that is a bad explanation because it does not address how the knowledge of how to create such designs could possibly have been created. (‘Who designed the designer?’, and so on.) But the argument from design can be used in valid ways too, and indeed its earliest known use, by the ancient Athenian philosopher Socrates, was valid. This issue was: given that the gods have created the world, do they care what happens in it? Socrates’ pupil Aristodemus had argued that they do not. Another pupil, the historian Xenophon, recalled Socrates’ reply:
SOCRATES: Because our eyes are delicate, they have been shuttered with eyelids that open when we have occasion to use them . . . And our foreheads have been fringed with eyebrows to prevent damage from the sweat of the head . . . And the mouth set close to the eyes and nostrils as a portal of ingress for all our supplies, whereas, since matter passing out of the body is unpleasant, the outlets are directed hindwards, as far away from the senses as possible. I ask you, when you see all these things constructed with such show of foresight, can you doubt whether they are products of chance or design?
ARISTODEMUS: Certainly not! Viewed in this light they seem very much like the contrivances of some wise craftsman, full of love for all things living.
SOCRATES: And what of the implanting of the instinct to procreate; and in the mother, the instinct to rear her young; and in the young, the intense desire to live and the fear of death?
ARISTODEMUS: These provisions too seem like the contrivances of someone who has determined that there shall be living creatures.
Socrates was right to point out that the appearance of design in living things is something that needs to be explained. It cannot be the ‘product of chance’. And that is specifically because it signals the presence of knowledge. How was that knowledge created?
However, Socrates never stated what constitutes an appearance of design, and why. Do crystals and rainbows have it? Does the sun, or summer? How are they different from biological adaptations such as eyebrows?
The issue of what exactly needs to be explained in an ‘appearance of design’ was first addressed by the clergyman William Paley, the finest exponent of the argument from design. In 1802, before Darwin was born, he published the following thought experiment in his book Natural Theology. He imagined walking across a heath and finding a stone, or alternatively a watch. In either case, he imagined wondering how the object came to exist. And he explained why the watch would require a wholly different kind of explanation from that of the stone. For all he knew, he said, the stone might have lain there for ever. Today we know more about the history of the Earth, so we should refer instead to supernovae, transmutation and the Earth’s cooling crust. But that would make no difference to Paley’s argument. His point was: that sort of account can explain how the stone came to exist, or the raw materials for the watch, but it could never explain the watch itself. A watch could not have been lying there for ever, nor could it have formed during the solidification of the Earth. Unlike the stone, or a rainbow or a crystal, it could not have assembled itself by spontaneous generation from its raw materials, nor could it be a raw material. But why not, exactly, asked Paley: ‘Why should not this answer serve for the watch as well as for the stone; why is it not as admissible in the second case as in the first?’ And he knew why. Because the watch not only serves a purpose, it is adapted to that purpose:
For this reason, and for no other, viz., that, when we come to inspect the watch, we perceive (what we could not discover in the stone) that its several parts are framed and put together for a purpose, e.g., that they are so formed and adjusted as to produce motion, and that motion so regulated as to point out the hour of the day.
One cannot explain why the watch is as it is without referring to its purpose of keeping accurate time. Like the telescopes that I discussed in Chapter 2, it is a rare configuration of matter. It is not a coincidence that it can keep time accurately, nor that its components are well suited to that task, nor that they were put together in that way rather than another. Hence people must have designed that watch. Paley was of course implying that all this is even more true of a living organism – say, a mouse. Its ‘several parts’ are all constructed (and appear to be designed) for a purpose. For instance, the lenses in its eyes have a purpose similar to that of a telescope, of focusing light to form an image on its retina, which in turn has the purpose of recognizing food, danger and so on.
Actually, Paley did not know the overall purpose of the mouse (though we do now – see ‘Neo-Darwinism’ below). But even a single eye would suffice to make Paley’s triumphant point – namely that the evidence of apparent design for a purpose is not only that the parts all serve that purpose, but that if they were slightly altered they would serve it less well, or not at all. A good design is hard to vary:
If the different parts had been differently shaped from what they are, of a different size from what they are, or placed after any other manner, or in any other order, than that in which they are placed, either no motion at all would have been carried on in the machine, or none which would have answered the use that is now served by it.
Merely being useful for a purpose, without being hard to vary while still serving that purpose, is not a sign of adaptation or design. For instance, one can also use the sun to keep time, but all its features would serve that purpose equally well if slightly (or even massively) altered. Just as we transform many of the Earth’s non-adapted raw materials to meet our purposes, so we also find uses for the sun that it was never designed or adapted to provide. The knowledge, in that case, is entirely in us – and in our sundials – not in the sun. But it is embodied in the watch, and in the mouse.
So, how did all that knowledge come to be embodied in those things? As I said, Paley could conceive of only one explanation. That was his first mistake:
The inference we think is inevitable, that the watch must have had a maker . . . There cannot be design without a designer; contrivance without a contriver; order without choice; arrangement without anything capable of arranging; subserviency and relation to a purpose without that which could intend a purpose; means suitable to an end . . . without the end ever having been contemplated or the means accommodated to it. Arrangement, disposition of parts, subserviency of means to an end, relation of instruments to a use imply the presence of intelligence and mind.
We now know that there can be ‘design without a designer’: knowledge without a person who created it. Some types of knowledge can be created by evolution. I shall come to that shortly. But it is no criticism of Paley that he was unaware of a discovery that had yet to be made – one of the greatest discoveries in the history of science.
However, although Paley was spot on in his understanding of the problem, he somehow did not realize that his proposed solution, creationism, does not solve it, and is even ruled out by his own argument. For the ultimate designer for whose existence Paley was arguing would also be a purposeful and complex entity – certainly no le
ss so than a watch or a living organism. Hence, as many critics have since noticed, if we substitute ‘ultimate designer’ for ‘watch’ in Paley’s text above, we force Paley to ‘the [inevitable] inference . . . that the ultimate designer must have had a maker’. Since that is a contradiction, the argument from design as perfected by Paley rules out the existence of an ultimate designer.
Note that this is not a disproof of the existence of God, any more than the original argument was a proof. But it does show that, in any good explanation of the origin of biological adaptations, God cannot play the role assigned by creationism. Though this is the opposite of what Paley believed he had achieved, none of us can choose what our ideas imply. His argument has universal reach for anything that has, by his criterion, the appearance of design. As an elucidation of the special status of living things, and in setting a benchmark that explanations of knowledge-laden entities must meet if they are to make sense, it is essential to understanding the world.
Lamarckism
Before Darwin’s theory of evolution, people had already been wondering whether the biosphere and its adaptations might have come into existence gradually. Darwin’s grandfather Erasmus Darwin (1731–1802), a stalwart of the Enlightenment, was among them. They called that process ‘evolution’, but the meaning of the word then was different from its primary one today. All processes of gradual improvement, regardless of their mechanism, were known as ‘evolution’. (That terminology survives to this day in casual usage and as a technical term in, of all places, theoretical physics, where ‘evolution’ means any sort of continuous change that one is explaining through laws of physics.) Charles Darwin distinguished the process that he discovered by calling it ‘evolution by natural selection’ – though a better name would have been ‘evolution by variation and selection’.
As Paley might well have recognized if he had lived to hear of it, ‘evolution by natural selection’ is a much more substantive mode of explanation than mere ‘evolution’. For the latter does not solve his problem, while the former does. Any theory about improvement raises the question: how is the knowledge of how to make that improvement created? Was it already present at the outset? The theory that it was is creationism. Did it ‘just happen’? The theory that it did is spontaneous generation.
During the early years of the nineteenth century, the naturalist Jean-Baptiste Lamarck proposed an answer that is now known as Lamarckism. Its key idea is that improvements acquired by an organism during its lifetime can be inherited by its offspring. Lamarck was thinking mainly of improvements in the organism’s organs, limbs and so on – such as, for instance, the enlargement and strengthening of muscles that an individual uses heavily, and the weakening of those that it seldom uses. This ‘use-and-disuse’ explanation had also been arrived at independently by Erasmus Darwin. A classic Lamarckian explanation is that giraffes, when eating leaves from trees whose lower-lying leaves were already eaten, stretched their necks to get at the higher ones. This supposedly lengthened their necks slightly, and then their offspring inherited the trait of having slightly longer necks. Thus, over many generations, long-necked giraffes evolved from ancestors with unremarkable necks. In addition, Lamarck proposed that improvements were driven by a tendency, built into the laws of nature, towards ever greater complexity.
The latter is a fudge, for not just any complexity could account for the evolution of adaptations: it has to be knowledge. And so that part of the theory is just invoking spontaneous generation – unexplained knowledge. Lamarck might not have minded that, because, like many thinkers of his day, he took the existence of spontaneous generation for granted. He even incorporated it explicitly into his theory of evolution: he guessed that, as successive generations of organisms are forced by his law of nature to take ever more complex forms, we still see simple creatures because a continuous supply of them is formed spontaneously.
Some have considered this a pretty vision. But it bears hardly any resemblance to the facts. Its most glaring mismatch is that, in reality, evolutionary adaptations are of a wholly different character from the changes that take place in an individual during its lifetime. The former involve the creation of new knowledge; the latter happen only when there is already an adaptation for making that change. For instance, the tendency of muscles to become stronger or weaker with use and disuse is controlled by a sophisticated (knowledge-laden) set of genes. The animal’s distant ancestors did not have those genes. Lamarckism cannot possibly explain how the knowledge in them was created.
If you were starved of vitamin C, your defective vitamin-C-synthesis gene would not thereby be caused to improve – unless, perhaps, you are a genetic engineer. If a tiger is placed in a habitat in which its colouration makes it stand out more instead of less, it takes no action to change the colour of its fur, nor would that change be inherited if it did. That is because nothing in the tiger ‘knows’ what the stripes are for. So how would any Lamarckian mechanism have ‘known’ that having fur that was a tiny bit more striped would slightly improve the animal’s food supply? And how would it have ‘known’ how to synthesize pigments, and to secrete them into the fur, in such a way as to produce stripes of a suitable design?
The fundamental error being made by Lamarck has the same logic as inductivism. Both assume that new knowledge (adaptations and scientific theories respectively) is somehow already present in experience, or can be derived mechanically from experience. But the truth is always that knowledge must be first conjectured and then tested. That is what Darwin’s theory says: first, random mutations happen (they do not take account of what problem is being solved); then natural selection discards the variant genes that are less good at causing themselves to be present again in future generations.
Neo-Darwinism
The central idea of neo-Darwinism is that evolution favours the genes that spread best through the population. There is much more to this idea than meets the eye, as I shall explain.
A common misconception about Darwinian evolution is that it maximizes ‘the good of the species’. That provides a plausible, but false, explanation of apparently altruistic behaviour in nature, such as parents risking their lives to protect their young, or the strongest animals going to the perimeter of a herd under attack – thereby decreasing their own chances of having a long and pleasant life or further offspring. Thus, it is said, evolution optimizes the good of the species, not the individual. But, in reality, evolution optimizes neither.
To see why, consider this thought experiment. Imagine an island on which the total number of birds of a particular species would be maximized if they nested at, say, the beginning of April. The explanation for why a particular date is optimal will refer to various trade-offs involving factors such as temperature, the prevalence of predators, the availability of food and nesting materials, and so on. Suppose that initially the whole population has genes that cause them to nest at that optimum time. That would mean that those genes were well adapted to maximizing the number of birds in the population – which one might call ‘maximizing the good of the species’.
Now suppose that this equilibrium is disturbed by the advent of a mutant gene in a single bird which causes it to nest slightly earlier – say, at the end of March. Assume that when a bird has built a nest, the species’ other behavioural genes are such that it automatically gets whatever cooperation it needs from a mate. That pair of birds would then be guaranteed the best nesting site on the island – an advantage which, in terms of the survival of their offspring, might well outweigh all the slight disadvantages of nesting earlier. In that case, in the following generation, there will be more March-nesting birds, and, again, all of them will find excellent nesting sites. That means that a smaller proportion than usual of the April-nesting variety will find good sites: the best sites will have been taken by the time they start looking. In subsequent generations, the balance of the population will keep shifting towards the March-nesting variants. If the relative advantage of having the best nesting sites is lar
ge enough, the April-nesting variant could even become extinct. If it arises again as a mutation, its holder will have no offspring, because all sites will have been taken by the time it tries to nest.
Thus the original situation that we imagined – with genes that were optimally adapted to maximizing the population (‘benefiting the species’) – is unstable. There will be evolutionary pressure to make the genes become less well adapted to that function.
This change has harmed the species, in the sense of reducing its total population (because the birds are no longer nesting at the optimum time). It may thereby also have harmed it by increasing the risk of extinction, making it less likely to spread to other habitats, and so on. So an optimally adapted species may in this way evolve into one that is less ‘well off’ by any measure.
If a further mutant gene then appears, causing nesting still earlier in March, the same process may be repeated, with the earlier-nesting genes taking over and the total population falling again. Evolution will thus drive the nesting time ever earlier, and the population lower. A new equilibrium would be reached only when the advantage to an individual bird’s offspring of getting the very best nesting site was finally outweighed by the disadvantages of slightly earlier nesting. That equilibrium might be very far from what was optimal for the species.
A related misconception is that evolution is always adaptive – that it always constitutes progress, or at least some sort of improvement in useful functionality which it then acts to optimize. This is often summed up in a phrase due to the philosopher Herbert Spencer, and unfortunately taken up by Darwin himself: ‘the survival of the fittest’. But, as the above thought experiment illustrates, that is not the case either. Not only has the species been harmed by this evolutionary change, every individual bird has been harmed as well: the birds using any particular site now have a harsher life than before, because they are using it earlier in the year.
The Beginning of Infinity Page 11