Complexity: Darwin and neutral evolution

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Is neutral evolution non-Darwinian?

„…Variations neither useful not injurious would not be affected by natural selection, and would be left either a fluctuating element, as perhaps we see in certain polymorphic species, or would ultimately become fixed, owing to the nature of the organism and the nature of the conditions.…”

Charles Darwin, Origin of species (1859)

See THE MODERN MOLECULAR CLOCK for a good overview of neutrality, and the molecular clock.

The importance of neutrality

Various authors have addressed the importance of neutrality to evolution. Peter Schuster, Peter Stadler, Walter Fontana, Mark Toussaint and Martijn Huynenhave explored the importance of neutrality on evolution.

Concepts such as innovation, modularity, evolvability, robustness seem to be all intricately linked to neutrality. Since there are 3 codons of 4 possible bases which encode for amino-acids, there are possible codes but there are only 20 amino-acids. This means that many changes in codons will neutral effects on the phenotype.

The effect of neutrality on evolution can be quite important. Without neutrality, evolution is often constrained to local fitness maxima, unable to progress to higher fitness values. Neutrality allows the genotype to ‘drift’ during these periods. This also explains why evolution often appears to go in spurts after periods of apparant stasis. And while the phenotype may be in stasis, because of the neutral evolution, the genotype isn’t.

adaptive.JPG

Adapted from: Peter Schuster

In other words, not only is neutral evolution NOT non-Darwinian or anti-Darwinian but it seems to be essential for evolvability.

In future contributions I hope to explore more of the ‘scale free’ nature of DNA, protein, RNA networks, the importance of neutrality on evolvability, robustness and modularity as well as information theoretical approaches to show how simple processes could have created the world as we know it.

Various references

Martijn Huynen, Exploring Phenotype Space Through Neutral Evolution, J Mol Evol. 1996 Sep;43(3):165-9

RNA secondary-structure folding algorithms predict the existence of connected networks of RNA sequences with identical secondary structures. Fitness landscapes that are based on the mapping between RNA sequence and RNA secondary structure hence have many neutral paths. A neutral walk on these fitness landscapes gives access to a virtually unlimited number of secondary structures that are a single point mutation from the neutral path. This shows that neutral evolution explores phenotype space and can play a role in adaptation.

Erik van Nimwegen, James P. Crutchfield, and Martijn Huynen, Neutral evolution of mutational robustness, Proc Natl Acad Sci U S A. 1999 August 17; 96 (17): 9716-9720

M. Toussaint, C. Igel (2002): Neutrality: A Necessity for Self-Adaptation . Proceedings of the Congress on Evolutionary Computation (CEC 2002), 1354-1359

M. Toussaint (2003): The evolution of genetic representations and modular neural adaptation. Submitted (in April) version of my PhD thesis; a revised, official version published as a booklet will follow.

14 Comments

I noticed this while reading OoS last month. Among my other compliments, I have to say the book is strikingly modern. He even vaguely anticipated things like Punc. Eq, though didn’t make that part of the theory.

Speaking of all this, I think one reason people argue with creationists is, it pains them to see someone missing such cool ideas. Some of the details of evolution are fantastic and enriching, there’s naturally a benevolent tendency among liberals to want to share that.

I know the point has been made many times, still…

I am always amazed how much of the Origin of Species remains valid after almost a century and a half. Darwin was an empiricist, but he sure seemed to have some sort of special insight into the nature of things.

…A rose by any other name.…

The problem is the same whether trying to fit evolving populations into rigid Linnean categories, or trying to give an evolving theory a fixed name.

A chief tactic of anti-evolutionists, and anti-science activists in general, is to exploit variable definitions to a public that cannot discern from context what is meant by authors. Is it any wonder that the anti-evolutionists’ favorite word is “Darwinism”?

Frnk J wrote

Is it any wonder that the anti-evolutionists’ favorite word is “Darwinism”?

I’m coming to like Wesley Elsberry’s use of “Paleyism” and “Paleyist”. That’s a meme worth propagating.

RBH

Paleyontologist

Took the words right outta my mouth. (Comment #4300)

Biography of Motoo Kimura - one of my heroes, in light of the fact that Japanese culture strongly discouraged creativity. Neutral evolution seems ordinary now, but it had to be forced down people’s throats the late 60s.

Russell wrote

Took the words right outta my mouth. (Comment #4300)

Sure enough. Kudos!

RBH

Syntax Error: mismatched tag at line 1, column 165, byte 165 at /usr/local/lib/perl5/site_perl/5.16/mach/XML/Parser.pm line 187.

Since the ID argument is essentially a religiously-motivated argument from incredulity about evolutionary theory, I think a more appropriate name for most of its proponents would be “Wilberforcists”, in honor of the famous Archbishop who challenged T.H. Huxley, and paid the price. It’s not as euphonious as “Paleyist”, but it has a nice sneering tone to it. ;-)

Andrea,

Might I suggest “Wilburforcers” instead? It’s a bit more mellifluous, and accentuates the intent of the proponents.

Problem with Wilberforce is that the more famous Wilberforce is known as a champion of the abolition of slavery. I knew about that Wilberforce - and rightfully so - long before I heard of his smaller-minded relative.

Also, to defend “Paleyist” - I don’t think it’s particularly a slur on the old guy himself. Heck, I’d be flattered to think I had an intellect comparable to Lamarck, but that doesn’t take away from the folly of a modern day Lamarckian.

I’m convinced Creationist is the best term. I mentioned earlier how scams change their names once people catch on, and I don’t see any reason to help them do that.

The problem with “Creationist” is that it is at once too exclusive, generally referring only to YEC, and too inclusive, possibly including even Theistic Evolution. Anti-evolution types are far too good at taking advantage of semantic loopholes.

Paleyist refers to anyone who tries to mangle science into apologetics.

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This page contains a single entry by PvM published on July 8, 2004 7:02 PM.

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