Irreducible Complexity: Fundemenatal Evolutionary Mechanism or Darwinian Dianetics?

[vampares]

Irreducible Complexity JAVA Applet(you will need a browser enabled Java VM)

 

This applet runs a "genetic selection" simulation. Basically it "homogenizes" the population. You have to run it fast (>>>) for a minute or two, or ~100 to ~2000 generations. The end result is a geneticly evolved piece that does not "evolve" anymore (that is to say, in my understanding, the removal of half the population always removes everything other than what is "IC").

 

Irreducible Complexity Demystified:

A new term, irreducibly complex, (IC) has been introduced into public discussions of evolution. The term was defined by Michael Behe in 1996 in his book Darwin's Black Box: The Biochemical Challenge to Evolution (1)

. . .

The argument from IC to ID is simply:

IC things cannot evolve

If it can't have evolved it must have been designed

. . .

"By irreducibly complex I mean a single system composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning."

. . .

IC refers to an organism doing something (the function) in such a way that the system (that portion of the organism that directly performs the function) has no more parts than are strictly necessary.

[lucaspa]

Behe created a strawman version of Darwinian evolution when he coined "irreducible complexity".

 

He used a quote from Origin of Species in which Darwin said "If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory [natural selection] would absolutely break down." pg 146

 

Behe then interpreted this as being a straight line modification from structure A to structure B. But notice Darwin didn't say this. All Darwin talked about was "numerous, succcessive, slight modifications".

 

There is an excellent paper out describing 4 routes of Darwinian evolution, all involving "successive, slight modifications" By using 1 or more of these routes, any IC system can be constructed. This paper is universally ignored by IDers; I have not seen even an attempt to answer it. I will give a summary of the paper below:

 

A Classification of Possible Routes of Darwinian Evolution

Richard H. Thornhill and Daviud W. Uussery J. theor. Biol. (2000) 203, 111-116

available online at http://www.idealibrary.com or http://www.cbs.dtu.dk/staff/dave/articles/jtb.pdf

 

"1. Introduction

 

It is generally assumed that Darwinian evolution must occur in a gradual, step-by-step manner, with natural selection acting at each step. A common argument used by anti-Darwinists involves the difficulty of explaining the origin of complex structures by such a process. However, there are several different mechanisms by which Darwinian evolution can occur. It is the purpose of this article to classify the different possible routes of Darwinian evolution. It is important to define four terms clearly before further discussion."

 

This paper is directed specifically at Behe and his "irreducible complexity" hypothesis. Remember Behe's specific claims: there is NO POSSIBLE Darwinian explanation for IC systems. Note that Thornhill and Ussery have already exposed one flaw of IC (and thus of ID), namely, that IDers make a strawman argument of Darwinian evolution to attack. This will become plainer in a bit.

 

The authors start out with definitions, the first being IC lifted right from Darwin's Black Box. They then define a term Behe missed:

 

"Functional Indivisibility

 

The quality of a component of a structure such that there is at least one alteration to it which would render the whole structure absolutely non-functional. This term was implied but not used by Behe (1996a, pp. 45, 142)."

 

The authors then define Darwinian evolution.

 

"Darwinian Evolution

 

Descent of organisms in which the following criteria are met: (i)

intergenerational differences are very much smaller than inter-specific ones; (ii) no intervention by conscious agent(s) occurs; (iii) the frequency of mutations or other heritable modifications is unrelated to functional utility; and (iv) selection is the sole means by which heritable modifications are accumulated to form functional structures."

 

I disagree that (ii) is part of Darwinian evolution. It certainly is not part of Origin of Species. However, if they mean "direct manufacture by conscious agent(s)", which is what they probably mean, then it is OK.

 

"Accessibility by Darwinian Evolution

 

The quality of a biological structure such that it could be generated by a sequence of very small changes, each of which is selectively neutral or advantageous (Darwin, 1859, p. 189; Dawkins, 1986, p. 91)."

 

"BACKGROUND

 

It was recently suggested that many biological structures are irreducibly complex, and therefore inaccessible by Darwinian evolution. Thus far, this is merely a restatement of the (fallacious) popular creationist argument about organs such as the eye. However, the new departure was to argue that the components of biochemical systems, unlike those of supramolecular structures, are single molecules, which are often functionally indivisible. The conclusion was that irreducibly complex structures of functionally indivisible

components are inaccessible by Darwinian evolution. Eukaryotic undulipodia (cilia and flagella), bacterial flagella, intracellular

vesicular transport, and the mammalian immune response and blood-

clotting systems were given as examples (Behe, 1996a).

The above thesis is unsound, as it is not certain either that any

biological structures are irreducibly complex, or that their

component molecules are functionally indivisible (Coyne, 1996;

Doolittle, 1997; Fulton, 1997; Ussery, 1999). However, the more

theoretical question about the accessibility by Darwinian evolution

of irreducibly complex structures of functionally indivisible

components, if such exist, has not been thoroughly examined. ... One

factor hampering examination of the accessibility of biological

structures by Darwinian evolution is the absence of a classification

of possible routes. A suggested classification is presented here."

 

So, let's get to the different routes of Darwinian evolution,and the

authors list 4.

"2.1 SERIAL DIRECT DARWINIAN EVOLUTION

 

This means change along a single axis. Although it can generate

complicated structures, it cannot generate irreducibly complex

structures. The components added may be functionally indivisible,

having originated by either mutation or adoption (see below), with a

probable example being the steps in an A -* B -* C -* D metabolic

pathway, such as the TCA cycle (Behe, 1996a,b). On the other hand,

they may be functionally divisible, with an example being increments

of giraffe neck length. A molecular example of the latter is the

gradual change in enzyme specificity and activity resulting from

single amino acid substitutions. "

 

"2.2 PARALLEL DIRECT DARWINIAN EVOLUTION

 

This means approximately synchronous changes in more than one

component, so that modification to other components always occurs

before the total modification to any one component has become

significant. For example, in the evolution of the eye of Nautilus,

and of the vertebrate eye if this passed through a Nautilus-like

stage (Land & Fernald, 1992), it would be necessary for the evolution

of the retina to be approximately synchronous with that of the

pinhole eye. The retina is accessible via small steps from a single

photosensitive cell, with increments of photosensitivity, and the

pinhole eye is likewise accessible from a minor concavity, with

incremental advantages initially in physical protection and then in

focusing (Nilsson & Pelger, 1994). However, neither component would

function without the other, and, furthermore, the retina would be

exposed to damage if not enclosed.

Parallel direct Darwinian evolution can generate irreducibly complex

structures, but not irreducibly complex structures of functionally

indivisible components (Fig. 1), and this is the valid conclusion to

draw from Behe's thesis."

 

So, Behe was correct about this, but the strawman argument is that

parallel direct Darwinian evolution is the ONLY route.

 

"As with serial direct Darwinian evolution, single steps in any of

the parallel routes may be functionally either divisible or

indivisible. Most complex supramolecular biological structures have

primarily this type of accessibility by Darwinian evolution, with

examples being bat echolocation, spiders' web construction, honeybee

waggle dances, and insect mimicry by orchids (Dawkins, 1986, 1995).

Some complex (but not irreducibly complex) molecular systems, such as

the globin proteins (Ptitsyn, 1999; Satoh et al., 1999), could also

have evolved in this manner."

 

"2.3 ELIMINATION OF FUNCTIONAL REDUNDANCY

 

For example, it is difficult to hypothesize a direct route by

Darwinian evolution from mammalian to reptilian jaws, as they consist

of different pairs of bones. However, the fossil intermediates

Morganucodon and Kuehneotherium had both quadrate-articular and

dentarysquamosal articulation. The following postulated evolutionary

sequence from reptilian to mammalian jaws, for which there is

considerable fossil evidence, involves selective advantage at each

step (Kermack & Kermack, 1984): ...Redundancy elimination can

generate irreducibly complex structures of functionally indivisible

components, and a Darwinian evolutionary route of this type has been

suggested for biochemical cascades, such as the blood-clotting system

(Robison, 1996)."

 

Oops. Generation of just those systems that Behe says cannot be

generated. Not generated by parallel direct evolution, but by

elimination of functional redundancy.

 

"2.4 ADOPTION FROM A DIFFERENT FUNCTION

 

For example, scale-feather intermediates would offer no aerodynamic

advantage, but one can hypothesize a sequence from scales to

primitive but airworthy feathers in which each step offers an

increased advantage as insulation. Their use for proto-flight

motility would therefore only begin after this sequence. Recently

discovered fossil evidence suggests that feather evolution did indeed

follow such a sequence, with protofeathers, composed of the same

proteins as feathers, in Sinosauropteryx (Chen et al., 1998; K.

Padian, pers. comm., 1999), probably marginally airworthy feathers in

the non-flying Caudipteryx and Protarchaeopteryx (Ji et al., 1998),

and feathers in the flying Archaeopteryx (Padian, 1998). The proto-

feathers and feathers probably also possessed functions in display,

camouflage, recognition, etc. and it is possible that the actual

sequence was more complicated than the above hypothetical one, with

evolution at some stages being driven primarily by selection for such

functions (Padian & Chiappe, 1998). However, the proto-feathers in

Sinosauropteryx were so thickly distributed that they almost

certainly did function as insulation (K. Padian, pers. comm., 1999).

Adoption from other functions, whether generating an irreducibly

complex structure or otherwise, appears to be widespread at the

molecular level. The following are a few examples:

(I) Many bacteria and yeasts contain chimeric flavohaemoglobins,

consisting of a haem domain which is homologous to non-chimeric haem

proteins, and a flavin-binding domain which is homologous to NADPH

sulphite reductase, toluate 1,2 dioxygenase, cytochrome P450

reductase, and nitric oxide synthase (Moens et al., 1996). (ii)

Antifreeze glycoprotein in the blood of Antarctic notothenioid

fishes, which enables them to survive in icy seas, is considered to

have evolved from a functionally unrelated pancreatic trypsinogen-

like protease, and the recent discovery of chimenc genes which encode

both the protease and an antifreeze glycoprotein polyprotein strongly

supports this theory (Cheng & Chen, 1999). (iii) Crystallins

(proteins with refractive functions in the eye lens) are closely

related or identical to stress-protective proteins in non-ocular

tissues (e.g. Drosophila alpha-crystallins and small heat-shock

proteins are homologous). Piatigorsky uses the term "gene-sharing"

for the encoding in a single gene of a protein with two or more

functions, and suggests that this may be a widespread

evolutionary "strategy" (Piatigorsky, 1998)."

 

Just to rub salt in the wound, Thornhill and Ussery go on to

demonstrate that one of Behe's examples of IC could arise this way:

 

"There are several apparent instances of adoption in one of Behe's

examples, the blood-clotting system. One is the kringle domain, a

structure of 90 amino acids with three characteristic disulphide

bonds, which is present in various proteins of the blood-clotting

cascade, and also in hepatocyte growth factor, which is not involved

in blood clotting (Gerhart & Kirschner, 1997, pp. 220-222). A second

example is epidermal growth factor, a 53 amino acid peptide with a

characteristic motif of six cysteines, which is present in several

blood-clotting proteins, and also in the epidermal growth factor

precursor, the low-density lipoprotein receptor, laminin (an

extracellular matrix protein), and several transmembrane receptors

(Davis, 1990)."

 

"There are two ways by which irreducibly complex structures of

functionally indivisible components could result from adoption:

 

(i) Generation of an irreducibly complex structure by the joining of two or more non-irreducibly complex structures of functionally indivisible components. A possible example is the V(D)J joining mechanism in the immune systems of jawed vertebrates, ...

(ii) Supply of an existing irreducibly complex structure of functionally indivisible components. The structure would have evolved previously by either redundancy elimination or the joining of two or more non-irreducibly complex structures of functionally indivisible components. Undulipodia may be accessible by Darwinian evolution in this manner, as their two main hypothesized origins are from ectosymbionts (Szathm ry, 1987) and spindle tubules (McQuade, 1977; Cavalier-Smith, 1978, 1982). However, the most detailed published hypothetical pathway for the transformation of ectosymbionts into undulipodia was actually one of parallel direct Darwinian evolution."

 

Again, remember Behe's claim. NO POSSIBLE Darwinian route. To refute

this claim, it is not necessary to show the actual route but only to

have a plausible route.

 

Thornhill and Ussery end up by comparing Dawkin's "brittle" structures to IC systems:

 

"Dawkins uses "brittleness" to mean the quality of a structure such

that it must be perfect if it is to work at all, and "brittle" is

therefore close or identical in meaning to irreducibly complex and

composed of functionally indivisible components. He argues that no

biological, and very few artificial, structures are "brittle", and

gives the arch as his sole example of one (Dawkins, 1995, pp. 82-

83). "

 

The authors then go on to show TWO routes of Darwinian evolution by

which the arch could have evolved.

 

"the arch would be accessible from a single cuboid by two routes of

Darwinian evolution: (i) via a heap of stones, which is then removed

(i.e. redundancy elimination); and (ii) from a lintel, by two lintels

being positioned diagonally and end to end, followed by the insertion

of a key stone, and then by the diagonals being replaced by stones

increasingly trapezoidal along one axis (i.e. parallel direct

Darwinian evolution). The latter is probably analogous to the actual

Roman route of invention,"

 

So, the whole concept of IC as evidence of ID is refuted by showing

the ways and combinations of ways an IC system can arise by Darwinian

evolution.