Tuesday, 15 May 2012

Are Bird Feathers and Avian Respiration Examples of Irreducibly Complex Systems?

[McIntosh 2009] considers birds' plumage and breathing apparatus as examples of irreducibly complex systems in the sense of Behe [Behe 1996]. Recall that an irreducibly complex system is a functional system which depends on a minimum of components each of which contributes to a function: remove any one or more components and the functionality is lost (also see my note here).

McIntosh argues that organisms, as complex cybernetic nano-machines, could not have possibly been self-organised bottom-up using the Darwinian mechanism which employs unguided natural selection over mutations resulting in multiple intermediate organisms. In such systems as bird plumage, respiration and many others, the removal of any component in practice is either unable to lead to a selectable advantage or lethal.

According to McIntosh, both the plumage and respiratory system

... are examples of the principle of specified functional complexity, which occurs throughout nature. There is no known recorded example of this developing experimentally where the precursor information or machinery is not already present in embryonic form. Such design features indicate non-evolutionary features being involved.

Fig. 1. Schematic of exaptation. Components that were part of irreducibly complex systems in ancestral forms (functions F1 and F2) are included (exapted) in an irreducibly complex system of a descendant form (function F3) as a result of a functional switch.

I would like to comment on this. First, despite the possibility of functional exaptation (fig.1) which leads to a functional switch (e.g. according to a popular evolutionary hypothesis, plumage first served for thermoregulation only, not for flight), in practical situations the probability of multiple coordinated functional switches is, as a rule, vanishingly small. On the other hand, in practice a gradualist sequence of functional switches appears to be implausible given the current estimates of available terrestrial probabilistic resources.

Furthermore, when analysing hypothetical phylogenetic trajectories of biosystems in the configuration space, it is important to realise that terminal points of these trajectories may belong to different and sometimes quite distant from each other attraction basins, in which case the trajectories themselves cross chaos incompatible with life. Also, the capability of functional switching itself is guaranteed by the semiotic processes in living organisms. Consequently, exaptation in practice always takes place in a given biological context and is limited by the capabilities of the built-in information processing systems (see my note here).

In addition, the macroevolutionary scenarios of what might have occurred are too vague in the face of experimental data [Behe 1996]. At the same time, fossil evidence is more against macroevolution than for it: while intermediate forms must really be numerous to give plausible grounds to macroevolution, the available fossils are too scanty and inconclusive [Dembski & Wells 2007].

Of course, macroevolutionary scenarios as explanations are usually on the favourable side (if you do not delve into detail) since it is extremely hard to exclude something as a possibility, which is exactly what the argumentation behind irreducible complexity is aiming to achieve. Indeed the burden of proof is always on the party claiming a theoretical or practical impossibility. This is why in the Roman law innocense is presumed: it is much easier to prove that a suspect could commit a crime rather than could not [Gene 2007].

Anyway, as more experimental data is being collected, teleology as a principle behind the functioning of the biosphere as a whole or individual organisms is becoming more convincing, while the case of unguided evolution is getting weaker. This said, the question of teleology is of course demarcational and therefore is rather philosophical.

Other papers by McIntosh are reviewed here.


  1. M. Behe (1996), Darwin's Blackbox.
  2. W. Dembski, J. Wells (2007), The Design of Life.
  3. M. Gene(2007), The Design Matrix.
  4. А.С. MacIntosh (2009), Evidence of Design in Bird Feathers and Avian Respiration, Intern. Jour. of Design & Nature and Ecodynamics, 2(4), pp.154-169. 
  5. Wikipedia, Demarcation problem.