Monday, April 16, 2007

Irreducible complexity, indeed...

Irreducible complexity is the hallmark of many anti-evolutionist arguments as it stipulates that many biological structures are too complex to have evolved from simpler, less-complex precursors. A common straw man is the mousetrap, whereby it is claimed that removing any part of the mousetrap makes it useless. (Biologist John McDonald elegantly dismembers this argument by describing a reducibly complex mousetrap). Anyway, such irreducible complexity is supposed to be proof of an intelligent designer (i.e., an immortal creator). Flagella, whip-like projections from some cells that are used for locomotion (see photo), are often claimed to be irreducibly complex biological structures. This view has been thoroughly discredited, even in a court of law (see Kitzmiller v. Dover).

A paper by Liu and Ochman in PNAS compiles further evidence against the hypothesis of irreducible complexity. They took advantage of full genome sequence for 41 bacterial species to trace the phylogenetic occurrence of flagellum proteins. The results show, amazingly, that the "core components of the bacterial flagellum originated through the successive duplication and modification of a few, or perhaps even a single, precursor gene." Flagella don't sound so irreducibly complex, then, do they? The take-home message is that evolutionary theory is sufficient to explain even the origin of complex organs and organelles and we needn't postulate intelligent designers. My compliments to Renyi Liu and Howard Ochman for a fine piece of work.


  1. Great find! The bacterial flagella doesn't look too rosy for the IDists these days.

  2. Yet another icon of ID ends up in the trash can.

    Must be tough being an IDiot these days.

  3. Must be tough being an IDiot these days.

    According to this report, the Discovery Institute may be having a particularly bad time.

  4. John,

    Carl Zimmer just pointed to your blog. You do a great job of writing for those who are interested in science but aren't used to the technical papers - and I am amazed at how much you have written within such a short space of time.

    I will be looking forward to the stuff on phages - something I have been following. Found out, for example, that archaea seem to be as affected by them as prokaryotes. I will be interested in the cryptic phages, genomic islands, the small world network and how its structure has been mapped in terms of the genetic sequence - which then has received further support in terms of protein analysis, suggesting that it is very ancient, etc.. I know there is a great deal coming out - and it is hard to keep up on it all.

    With regard to "irreducible complexity" (according to Behe's original definition rather than what it has gradually mutated into since) it turns out that it was predicted by Herman Muller back in 1918. Some information on this can be found here:

  5. And how do the ID'ers explain that homologous genes to those used by protists to make flagellae and ciliae, when they are mutated in humans, lead to human disease, unless evolution has happened in the meantime? I always wondered about that.