Precambrian rabbit

At one time, "Precambrian rabbits" or "fossil rabbits in the Precambrian" rock samples became popular imagery in debates about the validity of the theory of evolution and the scientific field of evolutionary biology. The images are reported to have been among responses given by the biologist, J.B.S. Haldane, when he was asked what evidence could destroy his confidence in the theory and the field of study. Many of his statements about his scientific research were popularized in his lifetime.

Some accounts use this response to rebut claims that the theory of evolution is not falsifiable by any empirical evidence. This followed an assertion by philosopher, Karl Popper, who had proposed that falsifiability is an essential feature of a scientific theory. Popper also expressed doubts about the scientific status of evolutionary theory, although he later concluded that the field of study was genuinely scientific.

Rabbits are mammals. From the perspective of the philosophy of science, it is doubtful whether the genuine discovery of mammalian fossils in Precambrian rocks would overthrow the theory of evolution instantly, although, if authentic, such a discovery would indicate serious errors in modern understanding about the evolutionary process. Mammals are a class of animals, whose emergence in the geologic timescale is dated to much later than any found in Precambrian strata. Geological records indicate that although the first true mammals appeared in the Triassic period, modern mammalian orders appeared in the Palaeocene and Eocene epochs of the Palaeogene period. Many, many millions of years separate this period from the Precambrian.

Not to be confused with a Precambrian rabbit, a zombie taxon is a fossil found in sediment or rock newer than the last appearance of the species in the fossil record. This is caused by erosion and natural rock formation, and is not a refutation of evolutionary theory.

Origin of the phrase
Several authors have written that J.B.S. Haldane (1892–1964) said that the discovery of a fossil rabbit in Precambrian rocks would be enough to destroy his belief in evolution. However these references date from the 1990s or later. In 1996 Michael J. Benton cited the 1993 edition of Mark Ridley's book Evolution, Richard Dawkins wrote in 2005 that Haldane was responding to a challenge by a "Popperian zealot". In 2004 Richa Arora wrote that the story was told by John Maynard Smith (1920–2004) in a television programme.

Theoretical background
The philosopher Karl Popper held that any scientific proposition must be falsifiable, in other words it must at least be possible to imagine an experiment whose outcome would disprove the hypothesis. Initially he thought that Charles Darwin's theory of natural selection (often summarized as "the survival of the fittest" ) was untestable in this sense, and therefore "almost tautological." Popper later changed his view, concluding that the theory of natural selection is falsifiable and that Darwin's own example of the peacock's tail had disproved one extreme variation of it, that all evolution is driven by natural selection. Although in 1978 Popper wrote that his earlier objection had been specifically to the theory of natural selection, in lectures and articles from 1949 to 1974 he had stated that "Darwinism" or "Darwin's theory of evolution" was a "metaphysical research programme" because it was not falsifiable. In fact he continued to express dissatisfaction with contemporary statements of the theory of evolution which focused on population genetics, the study of the relative frequencies of alleles (different forms of the same gene). Unfortunately some of the adjustments he proposed resembled Lamarckianism or saltationism, evolutionary theories that were and still are considered obsolete, and evolutionary biologists therefore disregarded his criticisms. In 1981 Popper complained that he had been misinterpreted as saying that "historical sciences" such as paleontology or the history of evolution of life on Earth were not genuine sciences, when in fact he believed they could make falsifiable predictions.

Further confusion arose in 1980–1981, when there was a long debate in the pages of Nature about the scientific status of the theory of evolution. None of the parties seriously doubted that the theory was both scientific and, according to current scientific knowledge, true. Some participants objected to statements that appeared to present the theory of evolution as an absolute scientific dogma, however, rather than as a hypothesis that so far has performed very well, and both sides quoted Popper in support of their positions. Some Creationists took this as an opportunity to declare that the theory of evolution was unscientific.

Would anachronistic fossils disprove evolution?
Evolutionary biologist Richard Dawkins said that the discovery of fossil mammals in Precambrian rocks would "completely blow evolution out of the water." Philosopher Peter Godfrey-Smith doubted that a single set of anachronistic fossils, however, even rabbits in the Precambrian, would disprove the theory of evolution outright. The first question raised by the assertion of such a discovery would be whether the alleged "Precambrian rabbits" really were fossilized rabbits. Alternative interpretations might include incorrect identification of the "fossils", incorrect dating of the rocks, and a hoax such as the Piltdown Man was shown to be. Even if the "Precambrian rabbits" turned out to be genuine, they would not instantly refute the theory of evolution, because that theory is a large package of ideas, including: that life on Earth has evolved over billions of years; that this evolution is driven by certain mechanisms; and that these mechanisms have produced a specific "family tree" that defines the relationships among species and the order in which they appeared. Hence, "Precambrian rabbits" would prove that there were one or more serious errors somewhere in this package, and the next task would be to identify the error(s).

Benton pointed out that, in the short term, scientists often have to accept the existence of competing hypotheses, each of which explains large parts&mdash;but not all&mdash;of the observed relevant data.