Dr Dave Regis
Karl Popper gave a great breath of fresh air to philosophy and to science when he suggested that the demarcation between Science and Not-Science was falsifiability. That is to say, a statement, to be scientific, must be able to be put to the test and, perhaps, be found wanting. This idea has been very influential and important. However, at one point in his thinking (1), Popper described the whole theory of evolution as not falsifiable, and therefore, Not-Science.
A zealous proponent of Popper’s philosophy once challenged the great British biologist J B S Haldane (*), one of the architects of the modern ‘synthetic’ theory of evolution, to name a single discovery which would falsify the theory of evolution. “Fossil rabbits in the Precambrian,” growled Haldane.
That’s a good line, but may need some explaining.
The earliest fossils of the group of mammals to which rabbits belong – the lagomorphs – are found in Mongolia and are dated to the Palaeocene Epoch (65 million years ago). It is thought that the hares and rabbits (Leporidae) split from the other lagomorphs (like the pika) in the following Oligocene Epoch (37 million years ago).
The Cambrian Period is when sediments aged 542-488 million years old were deposited. (Rocks of this age are best represented within Great Britain in Wales, after which the period was named.) Cambrian rocks bear some of the oldest fossils of complex, hard-bodied animals, including trilobites. Only a few poorly understood animal fossils are currently known from the end of the Pre-Cambrian Era – odd quilted shapes and small shelly things – so the appearance of such a latecomer to the show as a rabbit would be enormously difficult to explain, certainly overturning huge parts of what scientists currently think about the fossil record. In this way, the theory of evolution can be shown to be scientific in Popper’s terms, open to falsification, although no such fossils have ever been produced.
In a way, Darwin’s theory of natural selection can hardly be refuted, as it is a logical inference from what we know about heredity and the struggle for survival. If you accept both that organisms show inherited variation and also that these varieties experience differential survival, you are rather obliged to conclude that populations evolve, and will evolve in a way to adapt them better to their environment. I think this was what struck Huxley so forcibly on reading Darwin’s Origin of Species that he remarked, “How very stupid of me not to have thought of it before!“
See also David Love’s piece on falsification:
(*) Haldane helped develop the “modern synthesis” of “neo-Darwinian” evolutionary theory, combining the ideas of Darwin and Russell about natural selection with Mendelian genetics and mathematical models of changes in populations. He was also “one of the great rascals of science – independent, nasty, brilliant, funny and totally one of a kind” [Richard Milner, The Encyclopedia of Evolution, NY: Facts on File, 1990, pp. 207-08.].
His other much-quoted remark about evolution arose when he was asked by a cleric about what he could infer about character of the Creator, based on his wide ranging study of life. Haldane replied that the Creator must have “an inordinate fondness for beetles“.
OK so far? I now don Ben Goldacre’s Bad Science T-shirt, which proclaims “I think you’ll find it’s more complex than that”(2), to develop some concluding remarks:
1. Would Pre-Cambrian rabbits actually disprove the theory of evolution? Descent with modification through natural selection remains the best scientific explanation of an awful lot of observations. In fact, you can even watch it happen, in organisms with short life-spans, as when bacteria develop resistance to antibiotics. So I imagine that, rather than abandon evolutionary theory completely, science would prefer to salvage what they could. Nonetheless, such a remarkable discovery would blow a huge hole in lots of assumptions about fossil record, the repair of which would require vast sections of theory to be rebuilt.
2. The notion that evolution is not falsifiable is occasionally still trotted out as one of the many persistent myths or misconceptions about evolution (3). Popper did not advance his ideas as a criticism of the theory of evolution, and Popper himself changed his mind about the status of the theory, happy to describe it later as fully scientific (4), yet not because of Haldane’s remark.
Let’s look at Popper’s early view. Some ways of expressing Darwin’s ideas, like “survival of the fittest” seem “almost tautological” (Popper) – what does it mean to be fit, except that you survive? But since tautologies explain nothing, and Darwin’s ideas explain a great deal, there is something more going on here. Popper concluded that the best description for some theories, like evolution by natural selection, was a metaphysical research programme, an over-arching set of ideas which could not themselves be tested, but which might suggest some falsifiable statements, so driving research.
Unlike the Logical Positivists with whom he debated, Popper was not anxious to rid the world of metaphysics, and did not regard such a description as pejorative. For example, ideas that may be regarded as unfalsifiable metaphysics at one point in history (like the atomic theory of Democritus and Epicurus) might become falsifiable at a later time (that of Boyle and Dalton). So Popper, when he described the theory of evolution as one of these metaphysical research programmes, did not mean by it to dismiss it, and certainly not to describe it as meaningless or tautological. Rather, he thought it was useful and highly successful, just not falsifiable.
From this point of view, a Pre-Cambrian rabbit would falsify the scientific hypothesis that rabbits are a recent player on the evolutionary stage, but not refute the general ideas of the programme like evolution by natural selection.
3. Popper’s views themselves evolved. He later concluded that not only was the idea of evolution by natural selection falsifiable, it had indeed been falsified for some situations. For example, the variety of sequences of amino-acids in the haemoglobin molecules found in different creatures seems best explained by a non-selective mechanism of evolution called genetic drift, while Darwin’s own theory of sexual selection must be called upon to explain the existence of such manifest handicaps as the tail of a male peacock.
However, in searching for such examples, one is reminded about how very many features we see in organisms are indeed fit for their purpose, and the best explanation of how each came to be adapted for its function is Darwin’s theory of natural selection.
(1) Popper K. (2002). “Darwinism as a Metaphysical Research Programme” in Balashov Y and Rosenberg A. Philosophy of Science: Contemporary Readings. Routledge. pp.302-304. ISBN 0415257816.
(4) “I have changed my mind about the testability and the logical status of the theory of natural selection; and I am glad to have an opportunity to make a recantation.” Popper K (1978). “Natural Selection and the Emergence of Mind”. Dialectica, 32(3-4): 339-355. http://www3.interscience.wiley.com/cgi-bin/fulltext/120059156/PDFSTART