JR'S Free Thought Pages
The Facts of Life
Evolution: Fact and Theory
By Tim Wilkinson, PhD
Philosophy Now, May/June 2011
Almost one hundred and fifty years after the publication of Charles Darwin's On the Origin of Species, the February 2009 edition of Mathematics Today contained the following statement: "Many advocates of Darwinism would like us to believe that it is an established fact, whereas of course its status is that of a theory." Ronald Reagan thought evolution was "a scientific theory only" and George Bush said the jury was still out. Meanwhile, more than two hundred years after Darwin's birth, courts are being asked to decide whether alternatives to evolution should be taught in science classes. It is time to tackle the fact-versus-theory debate head on.
In the sense that any particular scientific theory is always an example of scientific theories in general, statements about Darwinism being a theory are correct, if rather empty. However, on closer inspection, the above uses of the word 'theory' seem like deliberate efforts to misdirect people into thinking there is more doubt over the veracity of evolution than is actually the case. The rhetorical device being deployed is known as 'equivocation'. Words can have more than one meaning, and oscillating between meanings can generate sufficient confusion that people can be led to accept a false conclusion. In this article, the problem words are 'Darwinism', 'evolution', 'theory', and 'fact'.
Consider 'Darwinism' and 'evolution'. It is important for clarity to separate two aspects of Darwin's work. First, he claimed that life on earth had developed gradually into new forms under the action of natural forces, each form arising as a modification of earlier ones. He was not alone in this claim: similar ideas can be traced from ancient Greek philosophers such as Epicurus and Lucretius, down to Jean-Baptiste Lamarck and Darwin's own grandfather, Erasmus Darwin. Towards the end of the eighteenth century paleontologists and biologists had established that extinction was possible, and evidence for gradual change of biological forms continued to accumulate during the first half of the nineteenth century. By the time Alfred Wallace's essay 'On The Tendency of Varieties to Depart Indefinitely from the Original Type' was presented to the Linnean Society of London in 1858, the notion that species change over time had already gathered considerable momentum. Darwin himself had put forward Wallace's paper for consideration, but members of the Society were already aware, by virtue of parts of Darwin's unpublished 1844 memoir, exhibited at the same meeting (neither of the two authors were present), that he had independently arrived at similar conclusions somewhat earlier. Second, however, the Origin, published on 24th November 1859, finally provided the nucleus around which a coherent picture of evolution was able to crystallize. In that book, for the first time ever, Darwin set out with supporting evidence a plausible and detailed mechanism explaining how evolution could have occurred. Even so, he did not use the term 'evolution' in the first edition of the Origin (he used it in later editions) other than indirectly, in the last word - 'evolved'.
The first source of confusion lies in muddling these two strands. 'Darwinism' should really be reserved for Darwin's particular theory of how the evolution of biological forms happens, as opposed to the assertion that it did happen somehow. Unfortunately, over time the term 'Darwinism' has been used less and less to describe Darwin's original theory, and more and more, by both supporters and critics, as a short hand for 'evolution' in the broad sense. This is probably down to Darwin's fame, which has inevitably made him the most renowned advocate of evolution in general. On top of this, many of the particulars of Darwin's original theory, most notably the idea of natural selection, still feature in modern evolutionary theory; and so we are left with the problem that without further clarification, the inclusion of 'Darwinism' in a sentence automatically results in ambiguity. But if 'Darwinism' can result in confusion, the use of the word 'theory' can result in total chaos.
The Facts about Theories
At one extreme of knowledge we have mathematical disciplines such as group theory and number theory. Such theories are part of a mathematical edifice whose proofs are as close as we're ever likely to get to certainty about anything. When number theory tells us there are infinitely many prime numbers, we can be sure of this conclusion with a degree of confidence that most other areas of our knowledge can only dream about. If truth is to be found anywhere at all, it is difficult to think of a better example than theories of this type. At the other end of the certainty spectrum, 'theory' is commonly used to refer to any exploratory conjecture, whether true, false, or slightly insane - such as the theory that crop circles are caused by visitors from outer space. Somewhere in the middle of this scale lie scientific theories, conspiracy theories, music theory, and goodness knows what else. Even within the bracket of scientific theories, there are different types. One could hardly say that string theory has the same degree of justification as the theory of photosynthesis. Despite crucial differences, the various types of theory are all designed to explain ideas, observations or facts, and this makes it very easy to confuse the different meanings of the word 'theory'. When someone says that 'Darwinism is a theory' it is therefore important to discover which sense of the words 'Darwinism' and 'theory' are being employed, and whether different meanings are being blurred, either accidentally, or deliberately as an argumentative move.
Such utterances often come from critics. It is unlikely in these cases that we are being urged to think that Darwinism is a theory similar to number theory, since that would put it on a par with the most certain truths we have at our disposal. Nor are we simply being asked to accept that Darwin's original scientific theory is a scientific theory, which would be trivially true. Perhaps then the term 'theory' is being used pejoratively to indicate that Darwinism might be, or actually is, incorrect? But even Darwin's current advocates would not deny that much of the Origin is incorrect, especially if we include errors of omission. For example, Darwin knew precisely nothing about DNA, which is a cornerstone of modern evolutionary theory. Modern evolutionary theories, such as 'neo-Darwinism' are very different from Darwin's in many respects, but are nevertheless trying to explain the same phenomenon, namely evolution. Therefore I further suspect that those who refer to Darwinism as being 'a theory' are trying to go beyond the un-contentious pronouncement that Darwin's theory of evolution has been replaced by a better theory, or even that modern evolutionary theories will in time doubtless be replaced by others that are better still. It is perfectly normal and unremarkable for scientific theories to change, or even be completely replaced by new ones, when the new theory fits observation better than the one it replaces, has better predictive power, or requires fewer assumptions. It therefore seems likely that we are being encouraged to go even further: 'Darwinism' is being used to mean 'evolution' in the broad sense, and 'theory' to mean a hypothesis or conjecture that might be, or actually is, untrue. In short, by saying Darwinism is (just) a theory, we are being asked to accept that evolution might not have happened. Equivocation is being employed to tempt people to agree to this idea, since everyone accepts that scientific theories exist in a world of competing alternatives and periodic revision.
In the sentence we examined at the beginning from Mathematics Today, the implication is further emphasized by contrasting 'theory' with 'fact'. Let's spell out the equivocation in more detail. In saying that 'Darwinism is a ‘theory', the statement that 'Darwin's scientific theory of how evolution happens is a scientific theory' - which is true by definition and which no reasonable person can therefore dispute - is being confused, perhaps deliberately, with 'the assertion that evolution happened somehow is mere conjecture'. If it's deliberate, the hope is that since reasonable people cannot question the former interpretation, they will be fooled into thinking they must accept the latter as well, or at least will not notice that the two meanings are different.
Don't be fooled by the word game. 'Evolution' in the broad sense - the spirit of what Darwin was trying to tell us 150 years ago - can no longer sensibly be described as a theory in the sense of ‘mere speculation', having long since slipped beyond the event horizon of reasonable doubt. People often mistakenly think that the fossil record is the main or even the only evidence for such a claim, but despite the compelling case that can be made from fossils alone, they in fact provide only a minority of the total evidence, which amongst other things is drawn from DNA analysis, embryonic development, geology, biochemistry, the geographical distribution of plants and animals, detailed observation of species over time, artificial selection, and anatomical comparisons of living creatures.
A Theory of Facts
Given the overwhelming evidence, is it really going too far to describe evolution using our other problem word, 'fact'? The Shorter Oxford English Dictionary defines a 'fact' as, 'A thing known for certain to have occurred or to be true' - which seems reasonable, but unfortunately this just shifts the difficulty onto the word 'certain'. Now, to an extremely skeptical mind - usually one belonging to a philosopher - no fact about the world is one hundred percent certain. As well as being prone to error, we can never completely rule out the possibility that we are dreaming, mad, or being tricked by Descartes' infamous demon. No sane person takes such hyper-skeptical scenarios seriously, except as interesting thought-experiments; but since we can make mistakes, there is a point to answer - namely, what kinds of support are sufficient to establish facts? It is certainly possible to devise narrow definitions of 'fact' which would exclude evolution. For example suppose the word was reserved for data which can be directly measured or unambiguously observed. The observation that whale and ammonite fossils have never been found together in the same strata of rock, or that human and chimpanzee DNA are almost identical, would then still count as a facts, but evolution itself would not.
In common with most assertions about past events, evolution is afflicted by what philosophers refer to as 'under-determination by the evidence', meaning that even large amounts of evidence can always be interpreted in more than one way. However, it is quite wrong to point to under-determination in isolation from other considerations, and claim that this means that evolution is not a fact. This abuse of under-determination is what is being attempted when one hears the following logical sleight-of-hand: "The evidence can be interpreted in many ways; therefore evolution is not a fact." Rather, explanations need to be weighed against each other to see which is the best or the most likely, and they need to be consistent with truths outside their immediate subject matter. If we try to interpret the evidence for evolution in some non-evolutionary way, we are led to disastrous conflicts with countless elementary direct physical observations and well-established facts of geology, biochemistry, genetics, physics, astronomy, and so on. We must therefore either conclude that evolution is the best explanation after all, or else abandon so many other uncontroversial areas of our knowledge that we would be left with hardly any facts whatsoever.
The availability of artificially narrow definitions and the problem of under-determination lend the veneer of intellectual respectability to claims that evolution does not qualify as a fact, but these concepts are being exploited to help limit the sense of the word 'fact' much too far beyond its valid use.
Consider the assertion that the Battle of Trafalgar actually took place, that is, that the battle is a fact. We have detailed written accounts of personnel, vessels, tactics, and plenty of physical evidence in the form of artifacts, although no one will ever know the precise movements of every ship, sailor and cannon involved. We certainly cannot observe the battle directly, because it took place more than two hundred years ago. Archaeological evidence could in principle be found which would alter our understanding of the events of 21st October 1805, and it is quite proper for historians to debate and revise the details. Further, like evolution, the fact of the Battle of Trafalgar is under-determined by the evidence. Documentary accounts can be forged, and physical evidence can be faked. But context, consistency, quantity, and especially quality of evidence also need to be taken into account in determining the battle as a fact. When they are we see that neither under-determination nor uncertainty over the particulars is sufficient to make it rational to deny that the battle ever took place. The gaps in our knowledge and inability to either fill in every detail or observe the events directly do not mean that the Battle of Trafalgar is just a theory. Yet it is no exaggeration to claim that the physical evidence supporting evolution is better - much better - than that which supports either the Battle of Trafalgar or virtually any other historical fact taught in our classrooms. Trilobites and tyrannosaurs have left us no written testimony, true; but the high-caliber physical evidence we do have is more than enough to compensate. The evidence supporting evolution is of better quality and immensely greater volume than that required in the United Kingdom to send a man to prison for life, or, in parts of the United States, to legally put him to death. If there are any known facts about the world at all, in the usual sense, then evolution is most certainly one of them, and one of the best supported facts at that. Nevertheless, it has to be admitted that the acute level of skepticism required to doubt it is indeed favored by some - such as those individuals who think the universe is just a few thousand years old, but for some bizarre reason has been constructed by God in such a way as to appear much older.
Evolution is sometimes described as 'both theory and fact', which is perfectly fair, and helps distinguish the two meanings. Evolution is a fact because it really did occur, and it's a theory when we're talking about explanations of how it occurred. Theories of (the fact of) evolution continue to improve, and occasionally they may change dramatically. The role of viruses, group selection and horizontal gene transfer between species are at this very moment being debated and tested against the evidence in order to try and determine their relative importance in evolutionary theory as a whole. Old ideas will be abandoned if they do not fit the evidence, and new ones will spring up to take their place. We will never reach the point where any theory of how evolution works can be declared either finally complete or totally correct; but this does not mean that evolution didn't happen. It did. The shameless scrambling of theories with facts - of evolution itself with evolutionary theories - is either sheer ignorance or sheer rhetorical subterfuge. Once people's logical compasses are set spinning by such chicanery, it is then easier to lead them towards the non sequitur that evolution is simply speculative, or worse, that alternative explanations, such as the supernatural, might be just as good, even when they are supported by poor evidence or no evidence at all. The whole line of reasoning is seriously defective, and often deliberately designed to confuse. Evolution should only be doubted by someone who is ready, on the basis of unsupported faith or effort of pure will, to reject any scientific fact about the material world whatsoever, no matter how high its stack of confirmatory physical evidence.
Facts and Faith
Like the realization that the earth goes around the sun, evolution is a fact about the way the world really is which took a surprisingly long time to be noticed. Indeed, it would not be worth expending so many column inches pointing this out in philosophy magazines were it not for the fact that surveys continually show that a large proportion of the population do not accept it. Some people believe that life evolved as part of a process guided by God (and we will consider that possibility in a moment), but the number of individuals who believe that evolution did not happen at all is positively alarming. For example, according to the results of a large MORI survey conducted for the British Council published on 3rd July 2009, forty-three percent of people in the United States, and sixteen percent of people in the United Kingdom, believe that all life on earth was created by God in its current form. It is natural for such people to be on the front line of the 'it's just a theory' argument, but as we have seen, such reasoning is entirely specious and has been smuggled into the debate under the cloak of equivocation. There is even a rumor going round that the type of faith scientists place in physical evidence is no different from faith in the supernatural. Like the previous ruse, this 'faith in the evidence' argument also relies for its success on people temporarily misplacing their dictionaries whilst simultaneously taking leave of their senses. In the present use of the term, 'faith' is belief that does not rest on logical proof or material evidence, and so faith and evidence are nothing less than perpendicular yardsticks for the measurement of truth. Yet they are not even remotely comparable in their reliability as standards for accurate knowledge. If they were, then a person claiming that 'fire is hot' based on the evidence of thermometers or burned hands would be no more likely to be correct than someone claiming that 'fire is cold' based on faith alone.
What about the possibility referred to earlier, that evolution is a fact but that certain evolutionary steps required supernatural assistance? According to the survey mentioned, thirty-two percent of Americans and twenty-five percent of Britons subscribe to this modern variation on the 'argument from design'. Note that this stance should not be confused with the quite different belief that the laws of nature must have been designed by God to result in the formation of macroscopic objects and the evolution of life. This latter possibility is an example of a 'cosmic fine-tuning' argument. Such notions make for a fascinating debate in their own right, but since they are entirely compatible with both the fact and theory of evolution, there is no need to discuss them further here.
Returning to the idea of supernaturally-assisted evolution, note that from this point of view, the fact of evolution is not in dispute - the disagreement is over whether the regularities of nature that need to be suspended in order to make it work. Even a handful of sufficiently well-documented supernatural events might be sufficient to demonstrate that they happen, but in the absence of a single incontrovertible example, a gap in our understanding is evidence only of our own ignorance, not of divine intervention. Professor Sir Martin Rees famously said that absence of evidence is not evidence of absence, and in context - the search for extraterrestrial life - he was correct. But that reasoning only works in situations where we have not been able to inspect sufficient evidence. In the case of evolution, the evidence is so comprehensive that the reverse argument comes into play. If I search every corner of my kitchen and find no evidence of tomatoes, then it is always possible I have missed some, but the more likely conclusion is that they will not be on the menu tonight. As each supposed 'evolutionary mystery' is revealed to be the product of entirely natural processes, this is not only further evidence in support of evolution, but also evidence against supernatural explanations of it.
Darwin’s Magnificent Legacy
In summary then, it is possible to interpret statements like 'Darwinism is only a theory' in such a way that they are unobjectionable, but only at the expense of rendering them trivial. However, many readers will equate 'Darwinism' directly with 'evolution', and 'theory' with 'conjecture'. Taken this way, such statements have strayed over a logical boundary into the realm of double-talk. No doubt a century from now many current theories of evolution will indeed have been discarded - a fate they will share with large swathes of other scientific theories. No matter. Darwin's magnificent legacy is not in the small print. It is in what is arguably the most important set of realizations ever to dawn on any human so far: that life is evolving and has been doing so ever since it began. That the earth and the universe are ancient. That species arise, change, flourish and become extinct over vast geological timescales, as the result of the action of complex natural forces. That we are a part of nature, not separate from it. That we are related to other life forms. All of these statements are not 'only theories' - that is, assumptions or conjectures. They are facts. In the wake of Darwin's bicentenary year, and the 150th anniversary of the publication of his profound insights, we should not allow one of the pivotal moments in the evolution of our species to be dismissed as 'just a theory'.
© DR TIM WILKINSON 2011
Tim Wilkinson has a PhD in pure mathematics and is a former lecturer in the Department of Mathematics at the University of Newcastle-Upon-Tyne.
Link to original article: www.philosophynow.org/issue84/The_Facts_of_Life