According to philosopher of science Sir Karl Popper, a theory must be
falsifiable to qualify as scientific. Popper (1976, 151) said, "Darwinism
is not a testable scientific theory but a metaphysical research
- Popper's statement of nonfalsifiability was pretty mild, not as
extensive as it is often taken. He applied it only to natural
selection, not evolution as a whole, and he allowed that some testing
of natural selection was possible, just not a significant amount.
Moreover, he said that natural selection is a useful theory. A
"metaphysical research programme" was to him not a bad thing; it is an
essential part of science, as it guides productive research by
suggesting predictions. He said of Darwinism,
And yet, the theory is invaluable. I do not see how, without it, our
knowledge could have grown as it has done since Darwin. In trying to
explain experiments with bacteria which become adapted to, say,
penicillin, it is quite clear that we are greatly helped by the
theory of natural selection. Although it is metaphysical, it sheds
much light upon very concrete and very practical researches. It
allows us to study adaptation to a new environment (such as a
penicillin-infested environment) in a rational way: it suggests the
existence of a mechanism of adaptation, and it allows us even to
study in detail the mechanism at work. And it is the only theory so
far which does all that. (Popper 1976, 171-172)
Finally, Popper notes that theism as an explanation of adaptation "was
worse than an open admission of failure, for it created the impression
that an ultimate explanation had been reached" (Popper 1976, 172).
- Popper later changed his mind and recognized that natural selection is
testable. Here is an excerpt from a later writing on "Natural
Selection and Its Scientific Status" (Miller 1985, 241-243; see also
When speaking here of Darwinism, I shall speak always of today's
theory - that is Darwin's own theory of natural selection supported
by the Mendelian theory of heredity, by the theory of the mutation
and recombination of genes in a gene pool, and by the decoded genetic
code. This is an immensely impressive and powerful theory. The
claim that it completely explains evolution is of course a bold
claim, and very far from being established. All scientific theories
are conjectures, even those that have successfully passed many severe
and varied tests. The Mendelian underpinning of modern Darwinism has
been well tested, and so has the theory of evolution which says that
all terrestrial life has evolved from a few primitive unicellular
organisms, possibly even from one single organism.
However, Darwin's own most important contribution to the theory of
evolution, his theory of natural selection, is difficult to test.
There are some tests, even some experimental tests; and in some
cases, such as the famous phenomenon known as 'industrial melanism',
we can observe natural selection happening under our very eyes, as it
were. Nevertheless, really severe tests of the theory of natural
selection are hard to come by, much more so than tests of otherwise
comparable theories in physics or chemistry.
The fact that the theory of natural selection is difficult to test
has led some people, anti-Darwinists and even some great Darwinists,
to claim that it is a tautology [see CA500]. A tautology
like 'All tables are tables' is not, of course, testable; nor has it
any explanatory power. It is therefore most surprising to hear that
some of the greatest contemporary Darwinists themselves formulate the
theory in such a way that it amounts to the tautology that those
organisms that leave most offspring leave most offspring.
C. H. Waddington says somewhere (and he defends this view in other
places) that 'Natural selection . . . turns out ... to be a
tautology' ..4 However, he attributes at the same place to the theory
an 'enormous power. ... of explanation'. Since the explanatory power
of a tautology is obviously zero, something must be wrong here.
Yet similar passages can be found in the works of such great
Darwinists as Ronald Fisher, J. B. S. Haldane, and George Gaylord
Simpson; and others.
I mention this problem because I too belong among the culprits.
Influenced by what these authorities say, I have in the past
described the theory as 'almost tautological', and I have tried to
explain how the theory of natural selection could be untestable (as
is a tautology) and yet of great scientific interest. My solution
was that the doctrine of natural selection is a most successful
metaphysical research programme. It raises detailed problems in many
fields, and it tells us what we would expect of an acceptable
solution of these problems.
I still believe that natural selection works in this way as a
research programme. Nevertheless, 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. My recantation may, I hope, contribute a little to the
understanding of the status of natural selection.
Brush, Stephen G. 1994. Popper and evolution. Reports of the National
Center for Science Education 13(4)-14(1): 29.
Cole, John R. 1981. Misquoted scientists respond. Creation/Evolution