Irreducible complexity

Irreducible complexity (IC) involves the idea that certain biological systems cannot evolve by successive small modifications to pre-existing functional systems through natural selection. Irreducible complexity has become central to the creationist concept of intelligent design, but the scientific community, which regards intelligent design as pseudoscience, rejects the concept of irreducible complexity. Irreducible complexity is one of two main arguments used by intelligent-design proponents, alongside specified complexity.... a single system which is composed of several well-matched, interacting parts that contribute to the basic function, and where the removal of any one of the parts causes the system to effectively cease functioning.An irreducibly complex evolutionary pathway is one that contains one or more unselected steps (that is, one or more necessary-but-unselected mutations). The degree of irreducible complexity is the number of unselected steps in the pathway.A system performing a given basic function is irreducibly complex if it includes a set of well-matched, mutually interacting, nonarbitrarily individuated parts such that each part in the set is indispensable to maintaining the system's basic, and therefore original, function. The set of these indispensable parts is known as the irreducible core of the system.'We come now to Professor Weismann's endeavour to disprove my second thesis — that it is impossible to explain by natural selection alone the co-adaptation of co-operative parts. It is thirty years since this was set forth in 'The Principles of Biology.' In §166, I instanced the enormous horns of the extinct Irish elk, and contended that in this and in kindred cases, where for the efficient use of some one enlarged part many other parts have to be simultaneously enlarged, it is out of the question to suppose that they can have all spontaneously varied in the required proportions.''A complex adaptation is one constructed of several components that must blend together operationally to make the adaptation 'work'. It is analogous to a machine whose performance depends upon careful cooperation among its parts. In the case of the machine, no single part can greatly be altered without changing the performance of the entire machine.'...struck upon the brilliant idea of using an old, broken mousetrap as a spitball catapult, and it worked brilliantly.... It had worked perfectly as something other than a mousetrap.... my rowdy friend had pulled a couple of parts --probably the hold-down bar and catch-- off the trap to make it easier to conceal and more effective as a catapult... the base, the spring, and the hammer. Not much of a mousetrap, but a helluva spitball launcher.... I realized why mousetrap analogy had bothered me. It was wrong. The mousetrap is not irreducibly complex after all.An irreducibly complex system cannot be produced directly (that is, by continuously improving the initial function, which continues to work by the same mechanism) by slight, successive modifications of a precursor system, because any precursor to an irreducibly complex system that is missing a part is by definition nonfunctional. Irreducible complexity (IC) involves the idea that certain biological systems cannot evolve by successive small modifications to pre-existing functional systems through natural selection. Irreducible complexity has become central to the creationist concept of intelligent design, but the scientific community, which regards intelligent design as pseudoscience, rejects the concept of irreducible complexity. Irreducible complexity is one of two main arguments used by intelligent-design proponents, alongside specified complexity. Creation science presented the theological argument from design with assertions that evolution could not explain complex molecular mechanisms, and in 1993 Michael Behe, a professor of biochemistry at Lehigh University, presented these arguments in a revised version of the school textbook Of Pandas and People. In his 1996 book Darwin's Black Box he called this concept irreducible complexity and said it made evolution through natural selection of random mutations impossible. This was based on the mistaken assumption that evolution relies on improvement of existing functions, ignoring how complex adaptations originate from changes in function, and disregarding published research. Evolutionary biologists have published rebuttals showing how systems discussed by Behe can evolve, and examples documented through comparative genomics show that complex molecular systems are formed by the addition of components as revealed by different temporal origins of their proteins. In the 2005 Kitzmiller v. Dover Area School District trial, Behe gave testimony on the subject of irreducible complexity. The court found that 'Professor Behe's claim for irreducible complexity has been refuted in peer-reviewed research papers and has been rejected by the scientific community at large.' Michael Behe defined irreducible complexity in natural selection in his book Darwin's Black Box: