R M Cullen
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Darwin's theory of evolution by descent from a common ancestor through the mechanism of natural selection is often presented as a "fact", with the assertion often made by Professor Dawkins for example that any person not blinded by religion would see it as such. The next five lectures present some obvious problems with the theory, all of which were known to Darwin and all of which were acknowledged as problems by him
There is a story, which may even be true, that Professor Chen from China during a visit to the United States said "In China we can criticize Darwin, but not the government. In America, you can criticize the government, but not Darwin."
There are three central features to Darwin’s theory of evolution by natural selection.
About 530 million years ago almost all of the body plans we know today appeared, in marine fossils, over a period of about ten million years. There are few, if any, intermediate forms in the Pre-Cambrian fossils. This is the “Cambrian explosion”. It was recognized by Darwin as a serious problem for both his theory of evolution and his theory of evolution by natural selection.
The Cambrian explosion is inconsistent with gradualism, a central claim of Darwin’s theory of evolution by natural selection.
In 1972 Stephen Jay Gould and Niles Eldredge published a paper which introduced their theory of punctuated equilibrium (Evolution by jerks as opposed to the accepted evolution by creeps).
Gould and Eldredge were paleontologists. They studied fossils.
They were not the first to observe that the evidence of the fossil record was that new species often appeared abruptly (in fossil terms), remained static for tens of millions of years, and then disappeared abruptly.
Before Gould and Eldredge though, this observation of long periods of stasis (equilibrium) punctuated by relatively short periods of speciation was explained away as a consequence of the incompleteness of the fossil record. This is what Darwin thought.
From a Darwinian perspective this just has to be true. Gradualism is central to the theory of evolution by natural selection.
Unfortunately the fossil record is sufficiently complete now, more than one hundred and fifty years after Darwin’s theory was published, for scientists to be reasonably sure that stasis, not gradualism, is the norm. The fossil record is a record of relatively rapid speciation (on a time scale where a million years is rapid) followed by long periods of stasis.
These long periods of stasis encompass periods of great environmental change.
Gould and Eldredge theorized that the long period of stability or stasis was the result of natural selection acting at a species level to eliminate competitor species. Rapid speciation results in competition between species with one winner emerging quickly in geological time.
This was not seen by their colleagues in other biological disciplines as particularly helpful. It explained neither the rapid speciation nor the long period of stasis but attacked another of the three central tenets of Darwin’s theory (that natural selection acted on organisms).
The long periods of stasis can be explained within the natural selection model. Natural selection produces small changes. If those changes do not have a selective advantage they will not increase in prevalence in a population. What results over time is a population with more variability but the same mean. There may not even be more variability as interbreeding between organisms with different small changes may result in offspring with no changes.
The periods of rapid speciation, punctuation, can be explained on the basis that only those speciations which are associated with adaptations that confer a reproductive advantage survive in the fossil record. This is because these speciations rapidly lead to the extinction of the previous dominant species and its replacement with the new, better adapted species.
Whether or not one accepts these kinds of explanation for punctuated equilibrium there is no question that the result is unexpected and challenges Darwin’s theory of evolution by natural selection.
Punctuated equilibrium is a challenge to the claim that Darwin’s theory of evolution by natural selection is science rather than mere dogma.
For a claim to be scientific it must be falsifiable, at least in principle if not (yet) in practice.
Before Eldredge and Gould published their paper Darwinians believed the fossil record, when complete, would show gradual change.
Punctuated equilibrium was the opposite of what was predicted. It falsified the theory.
Yet, today, punctuated equilibrium is said to confirm Darwin’s theory. This is simple intellectual dishonesty. Darwin’s theory has had to be modified significantly (and awkwardly and in a not particularly convincing way) to accommodate a confirmed observation that is the opposite of what was confidently predicted.
The problem punctuated equilibrium poses for the claim that Darwin’s theory of evolution by natural selection is this – if the theory makes predictions but can accommodate observations that are the opposite of that predicted it is not science as it is not falsifiable.
J.B.S Haldane a famous evolutionary biologist is reported to have said that “rabbits in the pre-Cambrian” would falsify Darwin’s theory. But would they, or would they be explained as overlapping fossil deposits or in some other way?