When Darwin proposed his theory, he also gave a potential falsification:If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down.
– Origin, Chapter Six
Professor Behe proposed Irreducible Complexity as a way to meet Darwin’s falsification criterion. His original definition of Irreducible Complexity was:A single system composed of several well-matched, interacting parts that contribute to the basic function of the system, wherein the removal of any one of the parts causes the system to effectively cease functioning. (
Darwin’s Black Box, 39)
His original argument from Irreducible Complexity was:
- *]Irreducibly Complex systems cannot evolve.
*]Living organisms contain Irreducibly Complex systems.
*]Therefore parts of living organisms cannot have evolved.
Unfortunately for Professor Behe this argument fails at step one, IC systems can and do evolve. It is no criticism of Behe that he put forward a failed hypothesis; most scientific hypotheses fail. Indeed in this case it was a useful failure that lead to a lot of good work on exactly how complex systems, such as the blood clotting cascade and bacterial flagella, evolve. IC was a failure, but an interesting and useful failure.
Professor Behe reacted correctly to his failure – he amended his hypothesis to account for the new facts:
- *]Irreducibly Complex systems are unlikely to evolve.
*]Living organisms contain Irreducibly Complex systems.
*]Therefore parts of living organisms are unlikely to have evolved.
Since then Behe has been working on examining just how unlikely it is that IC systems can evolve. In 2004 he produced a paper on just this subject: Behe and Snoke, (2004) “Simulating evolution by gene duplication of protein features that require multiple amino acid residues”. Behe’s own figures from that paper showed that a small population of bacteria could evolve a simple IC system in about 20,000 years:We conclude that, in general, to be fixed in 10^8 generations, the production of novel protein features that require the participation of two or more amino acid residues simply by multiple point mutations in duplicated genes would entail population sizes of no less than 10^9.
Since 20,000 years is not a long time and the population size Behe used (one billion) is small for bacteria – you have trillions of bacteria in your gut – it is evidence that it is really not very difficult for IC systems to evolve.
Behe’s IC argument was an interesting failure that lead to much good work in this area. However in the end it is not a valid argument against evolution.
Behe is incorrect, but that is not enough to make him a quack. He proposed a hypothesis which led to some interesting work, but ultimately failed. He was doing science.
rossum