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[[Creationism|Creationists]] have argued that evolution is not a scientific theory because it is not falsifiable, and in this respect they claim to have the support of Popper himself, as well as other evolutionists.

[[Creationism|Creationists]] have argued that evolution is not a scientific theory because it is not falsifiable, and in this respect they claim to have the support of Popper himself, as well as other evolutionists.

Although supporting evolution, [[Karl Popper]], leading philosopher of science and originator of the idea of [[Falsifiability as a Criterion of Demarcation of Science from Nonscience|falsifiability as a criterion of demarcation of science from nonscience]], said:<ref>{{hnb|Popper|1976|p=168}}</ref><ref name="popper">http://members.iinet.net.au/~sejones/PoE/pe05scnc.html</ref>

[[Karl Popper]], leading philosopher of science and originator of the idea of [[Falsifiability as a Criterion of Demarcation of Science from Nonscience|falsifiability as a criterion of demarcation of science from nonscience]], said:<ref>{{hnb|Popper|1976|p=168}}</ref><ref name="popper">http://members.iinet.net.au/~sejones/PoE/pe05scnc.html</ref>

{{QuoteBox|Darwinism is not a testable scientific theory, but a metaphysical research programme...

{{QuoteBox|Darwinism is not a testable scientific theory, but a metaphysical research programme...

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{{QuoteBox|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.<ref>Popper(1976) 171-172</ref>}}

{{QuoteBox|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.<ref>Popper(1976) 171-172</ref>}}

Popper later reevaluated this view.  In "Natural Selection and the Emergence of Mind", Popper wrote the following retraction:<ref>"Natural Selection and the Emergence of Mind", Dialectica, vol. 32, no. 3-4, 1978, pp. 339-355</ref>

Later in "Natural Selection and the Emergence of Mind", Popper wrote the following retraction:<ref>"Natural Selection and the Emergence of Mind", Dialectica, vol. 32, no. 3-4, 1978, pp. 339-355</ref>

{{QuoteBox|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.

{{QuoteBox|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.

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.}}  

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.}}  

While Popper maintained that "In its most daring and sweeping form, the theory of natural selection" was "not only refutable but actually refuted"<ref>Popper, 1978, pp.344-345</ref>, this criticism applied only to a subset of the natural selection model of evolution, and not evolutionary science as a whole.

While Popper maintained that "In its most daring and sweeping form, the theory of natural selection" was "not only refutable but actually refuted"<ref>Popper, 1978, pp.344-345</ref>, this criticism applied only to a subset of the natural selection model of evolution, and not evolutionary science as a whole.

He later reinfoced  this statement in a letter to the New Scientist in 1980:<ref>

He later wrote in a letter to the New Scientist in 1980:<ref>

Letter to New Scientist 87:611, 21 August 1980 </ref>

Letter to New Scientist 87:611, 21 August 1980 </ref>

This is a mistake, and I here wish to affirm that these and other historical sciences have in my opinion scientific character; their hypotheses can in many cases be tested."

This is a mistake, and I here wish to affirm that these and other historical sciences have in my opinion scientific character; their hypotheses can in many cases be tested."

Birch and Ehrlich have been characterised as considering evolution to be unfalsifiable, but this is incorrect. In ''Nature'':<ref>{{hnb|Birch and Ehrlich|1967|p=349}}</ref>{{QuoteBox|Our theory of evolution has become, as Popper described, one which cannot be refuted by any possible observations.  Every conceivable observation can be fitted into it.  It is thus outside of empirical science but not necessarily false.  No one can think of ways in which to test it.  Ideas, either without basis or based on a few laboratory experiments carried out in extremely simplified systems, have become part of an evolutionary dogma accepted by most of us as part of our training. The cure seems to us not to be a discarding of the modern synthesis of evolutionary theory, but more skepticism about many of its tenets" (Ehrlich and Birch, p. 352).}}  Ehrlich and Birch presented many objections to distinct hypotheses explaining certain aspects of contemporary evolutionary science, but not to the overarching theory itself.  A precis set in bold type at the beginning of the article states:

In ''Nature'':<ref>{{hnb|Birch and Ehrlich|1967|p=349}}</ref>{{QuoteBox|Our theory of evolution has become, as Popper described, one which cannot be refuted by any possible observations.  Every conceivable observation can be fitted into it.  It is thus outside of empirical science but not necessarily false.  No one can think of ways in which to test it.  Ideas, either without basis or based on a few laboratory experiments carried out in extremely simplified systems, have become part of an evolutionary dogma accepted by most of us as part of our training. The cure seems to us not to be a discarding of the modern synthesis of evolutionary theory, but more skepticism about many of its tenets" (Ehrlich and Birch, p. 352).}}  Ehrlich and Birch presented many objections to distinct hypotheses explaining certain aspects of contemporary evolutionary science, but not to the overarching theory itself.  A precis set in bold type at the beginning of the article states:

{{QuoteBox|While accepting evolutionary theory, should ecologists be more skeptical about hypotheses derived solely from untestable assumptions about the past? The authors put forward the view that many ecologists underestimate the efficacy of natural selection and fail to distinguish between phylogenetic and ecological questions.}}

{{QuoteBox|While accepting evolutionary theory, should ecologists be more skeptical about hypotheses derived solely from untestable assumptions about the past? The authors put forward the view that many ecologists underestimate the efficacy of natural selection and fail to distinguish between phylogenetic and ecological questions.}}