A system with N functional parts can only do the job it is suppose to do with N functional parts. If you reduce one of the parts from the system, say N-1 functional parts, the system simply cannot perform its function.
For what it is worth I fully agree with this definition of "Irreducible Complexity" ("IC"). The same system with N+1 functional parts is not IC because you can remove the +1 part and still function, you cannot remove any more without lose of the specific function used to define the ICness of the N parts.
I never really got the idea that really really complex means irreducibly complex.
And there is absolutely no reason for an IC system to be very complex, it could be as simple a system as N=2. Take away either part and the function ceases to happen: IC by definition.
The problem is that such a two part ({A}+{B}) system can easily evolve, in fact
{'FL' says 'almost' while 'BL' says 'absolutely'} every function starts this way.
Have more 'complex' IC systems evolved that we know of? Well first we need to define 'complex' ...
We could define it as the number of interactions between the parts necessary to achieve the function (so the complexity is dependent on the number of parts and the number of interactions - a three part function where {A} interacts with both {B} and {C} and {B} interacts with {C} thus has 3 'complexities', while a function where {A} interacts with {B} which then interacts with {C} only has 2 'complexities').
By this definition the above {A} + {B} system only has a 'complexity' of 1.
Ken Miller,
"A True Acid Test", says:
In 1982, Barry Hall of the University of Rochester began a series of experiments in which he deleted the bacterial gene for the enzyme beta-galactosidase. The loss of this gene makes it impossible for the bacteria to metabolize the sugar lactose.
An IC system with 1 part removed. Ceased to function.
Under appropriate selection conditions Hall found that the bacteria evolved not only the gene for a new beta-galactosidase enzyme (called the evolved beta-galactosidase gene, or ebg), but also a control sequence that switched the new gene on when glucose was present.
Two different parts evolved to replace the lost function.
Finally, a new chemical reaction evolved as well, producing allolactose, the chemical signal that normally switches on the lac permease gene, allowing lactose to flow into the cell.
A third part evolved to allow the other two to operate.
All well and good, eh? Just evolving new parts to replace damaged parts ... just adding to the system eh?
... once the (beta-galactosidase enzyme) gene was deleted, three components had to evolve to replace its function: First, a new galactosidase enzyme, second, a new lactose-sensitive control region, and third, a new way to switch on the lac permease gene.
Well here's the kicker:
Does Barry Hall's ebg system fit the definition of irreducible complexity? Absolutely. The three parts of the evolved system are:
(1) A lactose-sensitive ebg repressor protein that controls expression of the galactosidase enzyme
(2) The ebg galactosidase enzyme
(3) The enzyme reaction that induces the lac permease
Unless all three are in place, the system does not function, which is, of course, the key element of an irreducibly complex system.
The new system is by definition an IC (sub)system.
Now this may seem to be only an {A}+({B}+{C}) system (complexity = 2) but it is only part of the system, because the function is to metabolize the sugar lactose.
Logically the function could involve any number of parts {N} (minimum 'complexity' = N-1 for a linear process), and the loss of one part can be replace by the evolution of new part(s).
The new system may need more parts than the original (here we have N-1+3 = N+2) ... so it may actually be
more 'complex' afterwards ... obviously, then, increased 'complexity' is not a marker for excluding evolution from the process.
Later evolution may replace other parts with fewer parts ... part {Q} could replace parts {J} and {G} ... or replace single parts (damaged by other means) with additional increased numbers of parts.
The number of parts necessary for the function is not critical to the organism, what is critical is that the function be performed. Once that criteria is met then the organism is free to evolve methods to reduce the 'complexity' (ie use less resources for the same viability), and when this happens then natural selection would operate to the advantage of the reduced system over the more 'complex' one.
One can thus argue that 'IC' is a necessary outcome of natural selection on organisms with complex functions, as it would operate to remove any unnecessary parts from the functionality.
What does this all mean?
(1) That IC systems are not indicative of non-evolutionary process, rather they should be frequently observed and occurring often in evolved organisms.
(2) That IC is invalidated as a marker of "intelligent design" ("ID") -- because any number of any level of 'complexity' IC systems can freely and easily evolve.
(3) That anyone still using IC to promote ID is not paying attention.
Note, above we have the statement:
"The same system with N+1 functional parts is not IC because you can remove the +1 part and still function, you cannot remove any more without lose of the specific function used to define the ICness of the N parts."
What is interesting is that once you phrase it like this you raise the possibility that adding a new part to function {X} and then removing a different part still leaves you with functionality -- it may be {X} and it may be {Y}.
It is also possible that you could add part {Q} and remove parts {J} and {G} for the same functionality (it may be {X} and it may be {Y}), thus simplifying the 'complexity' but arriving at another 'IC' conundrum of the ID logical fallacy of incredulity: "Gosh, how could that happen naturally"...
Enjoy.
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