Thus, although the existence of progress in the biosphere is what the theory of evolution is there to explain, not all evolution constitutes progress, and no (genetic) evolution optimizes progress.
What exactly has the evolution of those birds achieved during that period? It has optimized not the functional adaptation of a variant gene to its environment – the attribute that would have impressed Paley – but the relative ability of the surviving variant to spread through the population. An April-nesting gene is no longer able to propagate itself to the next generation, even though it is functionally the best variant. The early-nesting gene that replaced it may still be tolerably functional, but it is fittest for nothing except preventing variants of itself from procreating. From the point of view of both the species and all its members, the change brought about by this period of its evolution has been a disaster. But evolution does not ‘care’ about that. It favours only the genes that spread best through the population.
Evolution can even favour genes that are not just suboptimal, but wholly harmful to the species and all its individuals. A famous example is the peacock’s large, colourful tail, which is believed to diminish the bird’s viability by making it harder to evade predators, and to have no useful function at all. Genes for prominent tails dominate simply because peahens tend to choose prominent-tailed males as mates. Why was there selection pressure in favour of such preferences? One reason is that, when females mated with prominent-tailed males, their male offspring, having more prominent tails, found more mates. Another may be that an individual able to grow a large, colourful tail is more likely to be healthy. In any case, the net effect of all the selection pressures was to spread genes for large, colourful tails, and genes for preferring such tails, through the population. The species and the individuals just had to suffer the consequences.
If the best-spreading genes impose sufficiently large disadvantages on the species, the species becomes extinct. Nothing in biological evolution prevents that. It has presumably happened many times in the history of life on Earth, to species less lucky than the peacock. Dawkins named his tour-de-force account of neo-Darwinism The Selfish Gene because he wanted to stress that evolution does not especially promote the ‘welfare’ of species or individual organisms. But, as he also explained, it does not promote the ‘welfare’ of genes either: it adapts them not for survival in larger numbers, nor indeed for survival at all, but only for spreading through the population at the expense of rival genes, particularly slight variants of themselves.
Is it sheer luck, then, that most genes do usually confer some, albeit less than optimal, functional benefits on their species, and on their individual holders? No. Organisms are the slaves, or tools, that genes use to achieve their ‘purpose’ of spreading themselves through the population. (That is the ‘purpose’ that Paley and even Darwin never guessed.) Genes gain advantages over each other in part by keeping their slaves alive and healthy, just as human slave owners did. Slave owners were not working for the benefit of their workforces, nor for the benefit of individual slaves: it was solely to achieve their own objectives that they fed and housed their slaves, and indeed forced them to reproduce. Genes do much the same thing.
In addition, there is the phenomenon of reach: when the knowledge in a gene happens to have reach, it will help the individual to help itself in a wider range of circumstances, and by more, than the spreading of the gene strictly requires. That is why mules stay alive even though they are sterile. So it is not surprising that genes usually confer some benefits on their species and its members, and do often succeed in increasing their own absolute numbers. Nor should it be surprising that they sometimes do the opposite. But what genes are adapted to – what they do better than almost any variant of themselves – has nothing to do with the species or the individuals or even their own survival in the long run. It is getting themselves replicated more than rival genes.
Neo-Darwinism and knowledge
Neo-Darwinism does not refer, at its fundamental level, to anything biological. It is based on the idea of a replicator (anything that contributes causally to its own copying).* For instance, a gene conferring the ability to digest a certain type of food causes the organism to remain healthy in some situations where it would otherwise weaken or die. Hence it increases the organism’s chances of having offspring in the future, and those offspring would inherit, and spread, copies of the gene.
Ideas can be replicators too. For example, a good joke is a replicator: when lodged in a person’s mind, it has a tendency to cause that person to tell it to other people, thus copying it into their minds. Dawkins coined the term memes (rhymes with ‘dreams’) for ideas that are replicators. Most ideas are not replicators: they do not cause us to convey them to other people. Nearly all long-lasting ideas, however, such as languages, scientific theories and religious beliefs, and the ineffable states of mind that constitute cultures such as being British, or the skill of performing classical music, are memes (or ‘memeplexes’ – collections of interacting memes). I shall say more about memes in Chapter 15.
The most general way of stating the central assertion of the neo-Darwinian theory of evolution is that a population of replicators subject to variation (for instance by imperfect copying) will be taken over by those variants that are better than their rivals at causing themselves to be replicated. This is a surprisingly deep truth which is commonly criticized either for being too obvious to be worth stating or for being false. The reason, I think, is that, although it is self-evidently true, it is not self-evidently the explanation of specific adaptations. Our intuition prefers explanations in terms of function or purpose: what does a gene do for its holder, or for its species? But we have just seen that the genes generally do not optimize such functionality.
So the knowledge embodied in genes is knowledge of how to get themselves replicated at the expense of their rivals. Genes often do this by imparting useful functionality to their organism, and in those cases their knowledge incidentally includes knowledge about that functionality. Functionality, in turn, is achieved by encoding, into genes, regularities in the environment and sometimes even rule-of-thumb approximations to laws of nature, in which case the genes are incidentally encoding that knowledge too. But the core of the explanation for the presence of a gene is always that it got itself replicated more than its rival genes.
Non-explanatory human knowledge can also evolve in an analogous way: rules of thumb are not passed on perfectly to the next generation of users, and the ones that survive in the long run are not necessarily the ones that optimize the ostensible function. For instance, a rule that is expressed in an elegant rhyme may be remembered, and repeated, better than one that is more accurate but expressed in ungainly prose. Also, no human knowledge is entirely non-explanatory. There is always at least a background of assumptions about reality against which the meaning of a rule of thumb is understood, and that background can make some false rules of thumb seem plausible.
Explanatory theories evolve through a more complicated mechanism. Accidental errors in transmission and memory still play a role, but a much smaller one. That is because good explanations are hard to vary even without being tested, and hence random errors in the transmission of a good explanation are easier for the receiver to detect and correct. The most important source of variation in explanatory theories is creativity. For instance, when people are trying to understand an idea that they hear from others, they typically understand it to mean what makes most sense to them, or what they are most expecting to hear, or what they fear to hear, and so on. Those meanings are conjectured by the listener or reader, and may differ from what the speaker or writer intended. In addition, people often try to improve explanations even when they have received them accurately: they make creative amendments, spurred by their own criticism. If they then pass the explanation on to others, they usually try to pass on what they consider to be the improved version.
Unlike genes, many memes take different physical forms every tim
e they are replicated. People rarely express ideas in exactly the same words in which they heard them. They also translate from one language to another, and between spoken and written language, and so on. Yet we rightly call what is transmitted the same idea – the same meme – throughout. Thus, in the case of most memes, the real replicator is abstract: it is the knowledge itself. This is in principle true of genes as well: biotechnology routinely transcribes genes into the memories of computers, where they are stored in a different physical form. Those records could be translated back into DNA strands and implanted in different animals. The only reason this is not yet a common practice is that it is easier to copy the original gene. But one day the genes of a rare species could survive its extinction by causing themselves to be stored on a computer and then implanted into a cell of a different species. I say ‘causing themselves to be stored’ because the biotechnologists would not be recording information indiscriminately, but only information that met a criterion such as ‘gene of an endangered species’. The ability to interest biotechnologists in this way would then be part of the reach of the knowledge in those genes.
So, both human knowledge and biological adaptations are abstract replicators: forms of information which, once they are embodied in a suitable physical system, tend to remain so while most variants of them do not.
The fact that the principles of neo-Darwinist theory are, from a certain perspective, self-evident has itself been used as a criticism of the theory. For instance, if the theory must be true, how can it be testable? One reply, often attributed to Haldane, is that the whole theory would be refuted by the discovery of a single fossilized rabbit in a stratum of Cambrian rock. However, that is misleading. The import of such an observation would depend on what explanations were available under the given circumstances. For instance, misidentifications of fossils, and of strata, have sometimes been made and would have to be ruled out by good explanations before one could call the discovery ‘a fossilized rabbit in Cambrian rock’.
Even given such explanations, what would have been ruled out by the rabbit would be not the theory of evolution itself, but only the prevailing theory of the history of life and geological processes on Earth. Suppose, for instance, that there was a prehistoric continent, isolated from the others, on which evolution happened several times as fast as elsewhere, and that, by convergent evolution, a rabbit-like creature evolved there during the Cambrian era; and suppose that the continents were later connected by a catastrophe that obliterated most of the life forms on that continent and submerged their fossils. The rabbit-like creature was a rare survivor which became extinct soon afterwards. Given the supposed evidence, that is still an infinitely better explanation than, for instance, creationism or Lamarckism, neither of which gives any account of the origin of the apparent knowledge in the rabbit.
So what would refute the Darwinian theory of evolution? Evidence which, in the light of the best available explanation, implies that knowledge came into existence in a different way. For instance, if an organism was observed to undergo only (or mainly) favourable mutations, as predicted by Lamarckism or spontaneous generation, then Darwinism’s ‘random variation’ postulate would be refuted. If organisms were observed to be born with new, complex adaptations – for anything – of which there were no precursors in their parents, then the gradual-change prediction would be refuted and so would Darwinism’s mechanism of knowledge-creation. If an organism was born with a complex adaptation that has survival value today, yet was not favoured by selection pressure in its ancestry (say, an ability to detect and use internet weather forecasts to decide when to hibernate), then Darwinism would again be refuted. A fundamentally new explanation would be needed. Facing more or less the same unsolved problem that Paley and Darwin faced, we should have to set about finding an explanation that worked.
Fine-tuning
The physicist Brandon Carter calculated in 1974 that if the strength of the interaction between charged particles were a few per cent smaller, no planets would ever have formed and the only condensed objects in the universe would be stars; and if it were a few per cent greater, then no stars would ever explode, and so no elements other than hydrogen and helium would exist outside them. In either case there would be no complex chemistry and hence presumably no life.
Another example: if the initial expansion rate of the universe at the Big Bang had been slightly higher, no stars would have formed and there would be nothing in the universe but hydrogen – at an extremely low and ever-decreasing density. If it had been slightly lower, the universe would have recollapsed soon after the Big Bang. Similar results have been since obtained for other constants of physics that are not determined by any known theory. For most, if not all of them, it seems that if they had been slightly different, there would have been no possibility for life to exist.
This is a remarkable fact which has even been cited as evidence that those constants were intentionally fine-tuned, i.e. designed, by a supernatural being. This is a new version of creationism, and of the design argument, now based on the appearance of design in the laws of physics. (Ironically, given the history of this controversy, the new argument is that the laws of physics must have been designed to create a biosphere by Darwinian evolution.) It even persuaded the philosopher Antony Flew – formerly an enthusiastic advocate of atheism – of the existence of a supernatural designer. But it should not have. As I shall explain in a moment, it is not even clear that this fine-tuning constitutes an appearance of design in Paley’s sense; but, even if it does, that does not alter the fact that invoking the supernatural makes for a bad explanation. And, in any case, arguing for supernatural explanations on the grounds that a current scientific explanation is flawed or lacking is just a mistake. As we carved in stone in Chapter 3, problems are inevitable – there are always unsolved problems. But they get solved. Science continues to make progress even, or especially, after making great discoveries, because the discoveries themselves reveal further problems. Therefore the existence of an unsolved problem in physics is no more evidence for a supernatural explanation than the existence of an unsolved crime is evidence that a ghost committed it.
A simple objection to the idea that fine-tuning requires an explanation at all is that we have no good explanation implying that planets are essential to the formation of life, or that chemistry is. The physicist Robert Forward wrote a superb science-fiction story, Dragon’s Egg, based on the premise that information could be stored and processed – and life and intelligence could evolve – through the interactions between neutrons on the surface of a neutron star (a star that has collapsed gravitationally to a diameter of only a few kilometres, making it so dense that most of its matter has been transmuted into neutrons). It is not known whether this hypothetical neutron analogue of chemistry exists – nor whether it could exist if the laws of physics were slightly different. Nor do we have any idea what other sorts of environment permitting the emergence of life would exist under those variant laws. (The idea that similar laws of physics can be expected to give rise to similar environments is undermined by the very existence of fine-tuning.)
Nevertheless, regardless of whether the fine-tuning constitutes an appearance of design or not, it does constitute a legitimate and significant scientific problem, for the following reason. If the truth is that the constants of nature are not fine-tuned to produce life after all, because most slight variations in them do still permit life and intelligence to evolve somehow, though in dramatically different types of environment, then this would be an unexplained regularity in nature and hence a problem for science to address.
If the laws of physics are fine-tuned, as they seem to be, then there are two possibilities: either those laws are the only ones to be instantiated in reality (as universes) or there are other regions of reality – parallel universes* – with different laws. In the former case, we must expect there to be an explanation of why the laws are as they are. It would either refer to the existence of life or not. If it did, that would ta
ke us back to Paley’s problem: it would mean that the laws had the ‘appearance of design’ for creating life, but had not evolved. Or the explanation would not refer to the existence of life, in which case it would leave unexplained why, if the laws are as they are for non-life-related reasons, they are fine-tuned to create life.
If there are many parallel universes, each with its own laws of physics, most of which do not permit life, then the idea would be that the observed fine-tuning is only a matter of parochial perspective. It is only in the universes that contain astrophysicists that anyone ever wonders why the constants seem fine-tuned. This type of explanation is known as ‘anthropic reasoning’. It is said to follow from a principle known as the ‘weak anthropic principle’, though really no principle is required: it is just logic. (The qualifier ‘weak’ is there because several other anthropic principles have been proposed, which are more than just logic, but they need not concern us here.)
However, on closer examination, anthropic arguments never quite finish the explanatory job. To see why, consider an argument due to the physicist Dennis Sciama.
Imagine that, at some time in the future, theoreticians have calculated, for one of those constants of physics, the range of its values for which there would be a reasonable probability that astrophysicists (of a suitable kind) would emerge. Say that range is from 137 to 138. (No doubt the real values will not be whole numbers, but let us keep it simple.) They also calculate that the highest probability of astrophysicists occurs at the midpoint of the range – when the constant is 137.5.
The Beginning of Infinity Page 12