Evolution — evidence for and against

Evidence for evolution

Variation – natural selection – adaptation

Most natural species have considerable genetic variability which enables them to produce, in the course of reproduction, 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, professional biologists and public, that evolution – the whole story – is true.

Evidence against evolution

New genes

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’[1]; and that, although progress has been made on the theory of the population genetics of beneficial mutations, experimental data is far behind. [2]

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?).

Embryonic development and the genetic basis of morphological novelties

A crucial aspect of the requirement for genes is their role in embryonic development and the formation of morphological characteristics. How embryos develop, e.g. from a fertilised egg, used to be a complete mystery. However, since around the 1980s we have begun to discover something of the genetic and molecular mechanisms through which embryonic development is implemented. And this knowledge has substantial implications for evolution.

First, because of the sophistication of these mechanisms – entailing complex interplay of many components which individually are also complex – these mechanisms in themselves clearly present a formidable, probably insuperable, challenge to an evolutionary origin. For example see the interdependence of proteins.

Second, now that we know biological structures are formed through specific genetic and molecular mechanisms, it shows unequivocally that we can no longer think of biological tissues as indefinitely variable or plastic (as the 19th-century biologists such as Darwin did) and think that morphological novelties can arise simply through a series of small morphological changes, without any regard to the underlying genetic/molecular mechanisms.

What I particularly have in mind are the many putative scenarios for the evolution of new structures – such as eyes, legs, wings – which generally consider only how such structures might have arisen through a series of small morphological changes, without any regard for the genetic/molecular bases for such changes.

For example, Richard Dawkins suggests that just about any biological structure could evolve into any other via a series of small morphological changes (see here), provided only that the steps are small enough and the number of steps large enough (arguing that it’s just a question of making the intermediate steps small enough to have a good chance of happening).

And probably the best known example of this sort of approach is Nilsson and Pelger's model for the evolution of an eye, which simplistically follows the ideas of Darwin, who of course had very little knowledge of genetics and biochemistry.

It is evident that evolutionary thinking in this area has not embraced what we now know about embryonic development, in effect staying in the 19th century. And I suspect that this head-in-the-sand approach is not just an oversight, but also because biologists recognise that to take seriously the genetic/biochemical implications would expose a fatal flaw in their scenarios. For more on this see Neo-Darwinism.

Anomalous ‘homology’

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. A key example of this is the vertebrates: despite the similar appearance of the embryonic 'phylotypic stage' of different classes of vertebrates, this stage arises in remarkably diverse ways, and even the vertebrae form in different ways, which clearly shows that the vertebrates have not evolved from a common vertebrate ancestor.

Falsification

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. [4]

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. [5]

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!)

Openness

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.

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Page created March 2017, last revised May 2019.