Evolution – evidence for and against
Evidence for evolution
Variation – natural selection – adaptation
Most natural species have considerable genetic variability which enables them to produce a wide range of morphological variations. Natural selection favours advantageous variations, resulting in evolution, especially in terms of adaptation – perhaps to the environment, or in relation to prey and/or predators (see Introduction to evolution).
It is the exquisite adaptations, and co-adaptations of interacting species – which are numerous and widespread – that can be so impressive, and which we see so vividly in nature documentaries. And it is these striking demonstrations of evolution that persuade most people, professionals and public, that evolution – the whole story – is true.
Evidence against evolution
However, what is not widely appreciated is that the evolution we see arises from the mixing and segregation of genes that are already available; and that the scope for evolution is limited by the available genetic material.
A crucial assumption of the theory of evolution is that new genes have arisen in the past (and continue to arise) in order to fuel evolution – to enable the emergence of novel features. But there are formidable biochemical obstacles to the origin of new genes. And, although long-term evolution absolutely depends on the occurrence of advantageous mutations, there is a marked lack of evidence for them. For example, in recent reviews on the population genetics of mutations, the authors comment that advantageous mutations are ‘usually rare and difficult to observe’; and that, although progress has been made on the theory of the population genetics of beneficial mutations, experimental data is far behind. 
Unfortunately, the distinction between (i) evolution that occurs solely through mixing and segregating existing genes and (ii) evolution that requires new genes, is not widely recognised. And the confusion is not helped by the excessively wide / loose way in which the term ‘macroevolution’ is used – to include evolution that is due solely to segregating existing genes right up to the emergence of new phyla which necessarily would involve very many new genes (see What is the difference between microevolution and macroevolution?).
Homologous structures are seen as important evidence of shared ancestry, and hence of evolution; notably, the obvious similarities of the vertebrate skeleton are seen as having arisen from a common vertebrate ancestor.
A key criterion for homologues, if this evolutionary explanation is correct, is that they must be derived from equivalent embryonic tissues, and by comparable developmental processes. And the more we find out about embryonic development at the genetic and molecular level, the more we see that developmental processes cannot be tinkered with, so this reinforces the validity of this criterion.
However, it has been known for a long time – since at least Darwin – that there are substantial exceptions, and more are being uncovered. These anomalies don’t just remove homology as supportive evidence of evolution, they constitute clear evidence that the organisms in question are not derived from a common ancestor. And a key example of this is the vertebrates: in different groups of vertebrates, the vertebrae form embryonically in substantially different ways – so this refutes a common ancestor of vertebrates.
Unfortunately I studied for two science degrees without once being taught any philosophy of science. So it wasn’t until later that I learned about falsification – that no amount of evidence in support of a theory can prove it to be true, but even a rather small amount of well-attested and properly interpreted evidence can show it to be false.
I am not being unrealistic about this. As I say in Evolution under the microscope, ‘there is much to be said for not abandoning a useful theory too readily’ (p 366); because, for example, there may be good explanations for the apparently conflicting data. On the other hand, neither can the principle of falsification be ignored.
Undoubtedly there is a considerable body of evidence consistent with evolution; but advocates of evolution are mistaken to see this as ‘proof’ that evolution is (completely) true. Proper weight should be given to contrary evidence.
And it’s not a question of comparing the amount of supporting evidence against the amount of contrary evidence, to see which is more. Rather, even if there is a large amount of evidence consistent with (and hence supporting) evolution, evolution is disproved by any reliable observation that is plainly contrary to it. For example, Darwin in the Origin, despite believing that his theory of evolution was supported by a wide range of evidence, accepted that:
If it could be demonstrated that any complex organ existed which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. 
A clear example of this misunderstanding or misrepresentation is Richard Dawkins’ book The Greatest Show on Earth: The evidence for evolution in which he presents a variety of evidence in support of evolution, portraying that this proves evolution is true.
Evolution is fact, and this book will demonstrate it. No reputable scientist disputes it, and no unbiased reader will close the book doubting it. 
But he conveniently ignores any evidence that is contrary to evolution. (And, of course, any scientist who doubts evolution, he would dismiss as non-reputable; and any reader who is not convinced must be biased against it!)
More importantly, neither can the contrary evidence be ignored! It seems that most scientists accept that scientific theories need to be held tentatively – always open to challenge from new data – except when it comes to evolution! It’s hard to know what’s really going on in another field to one’s own, but it seems to me that in other areas of scientific enquiry there is at least an openness about anomalous data; but it almost seems that in biology there is a conspiracy to hide any evidence that might challenge evolution. It is disturbing that text books etc. focus on the evidence that is consistent with evolution – usually portraying this as proof, and often mocking any who might think otherwise – and completely ignore any counter-evidence.
Notes display in the main text when the cursor is on the Note number.
1. Laurence Loewe and William G. Hill, 'The population genetics of mutations: good, bad and indifferent', Phil. Trans. R. Soc. B (2010) 365, 1153-1167, p1156.
2. H. Allen Orr, 'The population genetics of beneficial mutations', Phil. Trans. R. Soc. B (2010) 365, 1195-1201.
3. Stephen Meyer, Darwin's Doubt, HarperOne, 2013, px.
4. Charles Darwin, On the origin of Species, Penguin Classics (1968), p219; (first published 1859).
5. Richard Dawkins. The Greatest Show on Earth: The evidence for evolution. Black Swan edition, 2010, p9.
Page created March 2017, last revised February 2018.