Summary: Science is not a simple process of falsification of hypotheses. The philosophy of science is not just the views of Popper, which have some real problems. Evolution can be falsified in the usual meaning in scientific practice.

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t is often argued, by philosophers and creationists alike, that Darwinism is not falsifiable, and so is not science. This rests on the opinion that something is only science if it can be falsified, ie, proven wrong, at least in principle. This view, which is due to Popper, is not at all universally accepted, and some history of philosophy is in order to make sense of it and the criticisms made of it.[note 1]

At the time Darwin was formulating his view of evolution, the prevailing exemplar of science was the Newtonian program. Laws were paramount, and they determined the outcome. Science sought generalisations. Darwin tried to make a Newtonian science, and was hurt when the leaders of the field like Whewell and Herschel, two of his acquaintances and mentors, dismissed his theory as insufficiently like their model of science.[note 2]

William Whewell was the first real philosopher of science. He was heir to the English and Scottish schools of empirical commonsense. He rejected Hume's notion that induction (proving a rule or law by reference to singular examples of data and observation) was not correct, even if he didn't deny the logical force of the argument, that you cannot prove a universalisation no matter how many pieces of evidence you have to hand. Whewell proposed what he called the 'consilience of inductions' - the more inductive cases you have based on data, the more reliable the generalisation. This is what Darwin tried to attain, and partly explains why he spent so many years gathering case after case to bolster his theory. He thought he was doing it the Right Way [Ruse 1979].

Another school of thought was Positivism . This view affirmed that the only true knowledge was scientific knowledge, and that only positively established proofs were scientific knowledge. This meant the positivists had to be able to distinguish between real science and the pseudoscience of phrenology, spiritualism and the other crank theories coming onto the scene during the nineteenth century. One influential positivist was the physicist Ernst Mach of Mach speed fame, and from him grew a school of thought in the German-speaking countries of Europe known as Logical Positivism, centering on Vienna. The Logical Positivists held that something is science when it can be verified, and they had all kinds of rules for that, based on Hume's dictum that whatever does not logically follow from matters of fact or number was metaphysics. This was equivalent to saying it was literally nonsense for the positivists. When it was observed that the Verification Principle was unverifiable, and so nonsense, the school fell apart.

However it spurred the young Karl Popper [note 3] to put forward his own way of telling apart science (of which the exemplar was the new physics) from pseudoscience (of which the exemplars were Marxism and Freudianism). Popper also accepted the legitimacy of metaphysical statements, but denied they were any part of science. Popper's view (a variety of logical empiricism) was called 'falsificationism', and in its mature versions held that something is scientific just so far as it

(i) is liable to be falsified by data;

(ii) is tested by observation and experiment, and

(iii) makes predictions.

Real Scientists Make Predictions. This was the True Scientific Method. A minor quibble should be dealt with - Popper knew that the Falsification Principle could not be falsified. It was openly metaphysical. In this context, it makes sense why a pro-evolutionist like Popper called Darwinism a metaphysical research program. It was no more falsifiable (he thought) than the view that mathematics describes the world, and it was just as basic to modern biology [Popper 1974: sect 37].

The spanner in the works was first thrown by sociologists and historians of science, including Robert Merton, and later Thomas Kuhn. Kuhn's book [1962] in particular set the cat among the pigeons. If Popper thought that what he was doing was distilling the essence of science into a set of proscriptions, Kuhn and others observed that no science in fact looks like this model.

According to Kuhn, you can't even compare when one theory is better than another scientifically, for each global theory carries its own assessment methods. Change from one global theory to another is more akin to a religious conversion than a rational decision. Science only changes when the older theory can't cope with some arbitrary number of anomalies, and is in 'Crisis'. When this happens, the scientific community acts like someone looking at those dual-aspect pictures like the famous old crone/young woman picture. They 'snap' from one view to another, what Kuhn called a 'paradigm shift'. Science undergoes revolutions, and the only way to determine if something is scientific is to see what scientists do (there is an obvious circularity here).

This was very popular in the relativistic late 60s, but ran up against some serious problems. For a start, nobody could find these radical revolutions in the historical record. Even Galileo and Newton turned out to be revisionists rather than revolutionaries. Then, 'paradigm' started to be used for every new theory with impact on a discipline (which is all theories, in the end). Eventually, it became obvious that while Kuhn had made many interesting observations, there was no such universal cycle as he had proposed in the 'life' of a scientific theory. The very term 'paradigm' was attacked as being too vague [Masterman 1970], and Kuhn eventually dropped it in favour of more restricted terms like 'disciplinary matrix' and 'exemplar' [Kuhn 1970, 1972].

Kuhn's friend Paul Feyerabend [1970a, 1970b, 1975] stirred things even more by arguing that there was no such thing as the Scientific Method, either, something Kuhn held to exist in a more philosophical sense. Feyerabend argued that method was restricted to small subdisciplines, and that at any point any scientists could bring in anything from astrology to numerology if it helped. He even cheered on early recent creationism. This was the extreme end of the 'science is what scientists do' approach. Feyerabend wanted scientists to do anything they wanted, and call it science.

It was opposed by Imre Lakatos [1970], who argued that science was a historical series of research programs. So long as they were getting results, progressing from one problem to another, they were 'generating', otherwise they were 'degenerating'. According to Lakatos, a research program is a strongly protected core of theories that are relatively immune to revision, while ancillary theories are frequently revised or abandoned.

One thing all three of these philosophers thought in opposition to Popper - there was no point that could be ruled off as the dividing line between 'rational' science and 'non-rational' non-science. Lakatos identified what he called the Duhem-Quine Thesis - nothing can be falsified if you want to make suitable adjustments elsewhere in your theoretical commitments. Get a result that upsets your favoured theory of gravitation? Then the instrument's in error, or something is interfering with the observations, or there's another process you didn't know about, or some other background theory is wrong. And the point of this is that all these moves are actually used - they are rational in the sense of good scientific practice. Positivism is irretrievably dead by this stage.

So, what is the difference between science and non-science? There are several mutually compatible alternatives on the board. Pragmatism , the only philosophy to have originated in North America, holds that the truth or value of a statement like a theory or hypothesis lies in its practical outcomes. Pragmatists say that being scientific is a retroactive label given to what survives testing and makes a real practical difference, like a theory about a cancer affecting how that cancer is treated, more successfully. Progress in science is the accumulation of theories that work out [Laudan 1977].

Realists continue to say that what makes something scientific is its modelling reality successfully, and this has given rise to what is known as the Semantic Conception of Theories [Suppe 1975, 1989, see Ereshevksy 1991 for criticisms of this approach]. On this account, what science does is create effective models , and if a model meets Lakatos's criteria for a generating research program, those models are presumed to be adequate and true. And there is a sociological strain. This is divergent, but is either fully relativistic (science is just something that scientists construct for some social reasons of their own), or more pragmatist and realistic, and shares a strong commitment to the importance and uniqueness of science (eg, Hull [1988]).

Back to evolution. It becomes clear why the simple-minded parroting, even by scientists, that if it can't be falsified it isn't science, is not sufficient to rule out a theory. What science actually is, is a matter for extreme debate. The rediscovery post-Merton of the social nature of science has thrown eternal Scientific Methods out the window, but that doesn't mean that science is no longer distinguishable from non-science. It just isn't as easy as one would like in an ideal world. Last I looked, it wasn't an ideal world, anyway.

However, on the ordinary understanding of falsification, Darwinian evolution can be falsified. What's more, it can be verified in a non-deductive sort of way. Whewell was right in the sense that you can show the relative validity of a theory if it pans out enough, and Popper had a similar notion, called 'verisimilitude'. What scientists do, or even what they say they do, is in the end very little affected by a priori philosophical prescriptions. Darwin was right to take the approach he did

It is significant that, although it is often claimed that Darwinism is unfalsifiable, many of the things Darwin said have in fact been falsified. Many of his assertions of fact have been revised or denied, many of his mechanisms rejected or modified even by his strongest supporters (eg, by Mayr, Gould, Lewontin, and Dawkins), and he would find it hard to recognise some versions of modern selection theory as his natural selection theory. This is exactly what a student of the history of science would expect. Science moves on, and if a theory doesn't, that is strong prima facie evidence it actually is a metaphysical belief. [note 4]

A final quote from Hull [1988: 7] is instructive:

Yet another ambiguity constantly crops up in our discussions of scientific theories. Are they hypotheses or facts? Can they be "proved"? Do scientists have the right to say that they "know" anything? While interviewing the scientists engaged in the controversies under investigation, I asked, "Do you think that science is provisional, that scientists have to be willing to reexamine any view that they hold if necessary?" All the scientists whom I interviewed responded affirmatively. Later, I asked, "Could evolutionary theory be false?" To this question I received three different answers. Most responded quite promptly that, no, it could not be false. Several opponents of the consensus then current responded that not only could it be false but also it was false. A very few smiled and asked me to clarify my question. "Yes, any scientific theory could be false in the abstract, but given the current state of knowledge, the basic axioms of evolutionary theory are likely to continue to stand up to investigation."

Philosophers tend to object to such conceptual plasticity. So do scientists -- when this plasticity works against them. Otherwise, they do not mind it at all. In fact, they get irritated when some pedant points it out.

Most scientists are not philosophically inclined and will make use of whatever is a help in their work, but not in the way Feyerabend thought. Reflective scientists know that it's all how you ask the question that counts. Most physicists would not immediately think that atomic theory could be false, either. They are answering the question "is it likely to be dropped later on?" not the philosophical "could it in theory be dropped?" which is a different issue. Philosophers do conceptual tidying up, among other things, but scientists are the ones making all the sawdust in the workshop, and they need not be so tidy. And no cleaner should tell any professional (other than cleaners) how it ought to be done. Creationists who say, "evolution is not like what Popper said science should be, so it isn't science" are like the janitor who says that teachers don't keep their classrooms clean enough, so they aren't teachers.

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