Thursday, 2 August 2012

A critique of Richard Dawkins’ The Greatest Show on Earth: The evidence for evolution - cont...

4. Half-truths about proteins

It is clear Richard Dawkins realises that the complexity of embryological development poses a serious challenge to the theory of evolution, so he goes out of his way to gloss over the realities. The cornerstone of his approach is to try to argue that embryological development proceeds simply through the natural operation of local rules i.e. without an overall plan that would need a designer. I will explain subsequently how his attempted sleight of hand doesn’t work. Meantime ...

Unfortunately (for him), he tries to build up his case with reference to the structure of proteins; but it is his undoing because exposing his half-truths here makes it all the easier to explain the fallacy of trying to apply a similar approach to embryological development. As he says, proteins comprise linear sequences of amino acids, which fold up into a 3-dimensional structure which is essential for their biological function.

Protein molecules, simply by following the laws of chemistry and thermodynamics, spontaneously and automatically twist themselves into precisely shaped three-dimensional configurations. ... Any given sequence of amino acids dictates a particular folding pattern. (p236)

What he fails to say is that, simply because of the laws of chemistry and thermodynamics (his local rules), the vast majority of amino acid sequences will not fold at all. By not acknowledging this, he gives the false impression (false, but no doubt deliberate, as he must surely know this) that most amino acid sequences will fold in this way. Whereas in fact very few do - Douglas Axe estimated that only about 1 in 10^77 sequences have the potential to fold (Estimating the prevalence of protein sequences adopting functional enzyme folds; J Mol Biol 341(5):1295

Dawkins mentions only the specificity of proteins in terms of their ability to selectively bind their substrates (compounds they act on). What he ignores is their active sites - the parts of the proteins that have just the right chemical groups (derived from the right amino acids) in just the right places in relation to the bound substrates so as to catalyse reaction between them. Needless to say, taking these features on board as well, further compounds the specificity required of the amino acid sequence for e.g. an enzyme, and hence reinforces the prohibitive improbability against their arising by chance.

Dawkins comments that at present we are able to predict how some amino acid sequences will fold; and quite likely we will be able to do this for all before too long. But that’s only one side of the coin. What’s required is to identify an amino acid sequence that will fold, and once folded will perform a required biological function. Thanks to increased computing power and some ingenious programming, I expect that one day we will be able to design proteins to fold in a particular way, and maybe perform a particular function. But that will serve only to reinforce the case that functional proteins require a designer.

The nonsense that proponents of evolution would have us believe is that biologically active proteins, with their highly specific and hence improbable sequences, could arise by chance. Dawkins of course rolls out the usual evolutionary article of faith that complex proteins evolved from shorter/simpler precursors. But, as discussed more fully in my book, there are substantial objections to such a scenario.

  1. First is the question of folding. The forces between the packed amino acids (Dawkins’ local rules) that hold a protein in its folded state are so weak that there needs to be many amino acids involved, typically requiring a protein to be at least 70 amino acids long (see Protein structure and function by Jack Kyte) So it’s utter nonsense to suggest as some textbooks do, and Dawkins would have us believe, that proteins could have started off with just a handful of amino acids.
  2. Second is that key amino acids, such as those contributing to the active site, are generally scattered throughout the linear sequence of the protein, and are brought together only once the protein is folded. If proteins had evolved from short sequences, one would have thought that at least these critical amino acids (which necessarily would need to have been close together in a short protein) would still be grouped together; because to disperse them during the course of subsequent evolution would require constant restructuring of the protein.

It’s all very well for Dawkins to argue that proteins fold merely through the operation of local rules / natural forces. But what he fails to acknowledge is that operation of those rules results in something useful only if the underlying components are right - so far as proteins are concerned, that they have the right amino acid sequence. And the evidence clearly shows that natural selection acting on random mutations could not generate such sequences. Evolutionists merely cling to this hope as a drowning man clings to a straw.

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