Irreducible complexity

Authors: Alex Tee Neng Heng, Suzanne Sadedin

How can a simple, mechanical process like natural selection produce the awe-inspiring complexity and diversity of life on earth? This question has fascinated people ever since Charles Darwin proposed his theory of evolution. Biochemist Michael Behe claims that some biochemical systems cannot have evolved because they share a property he calls “irreducible complexity”, defined as follows:

“By irreducibly complex I mean a single system composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning.”

Behe’s argument forms the basis of “intelligent design theory” (ID). Despite the fact that ID lacks any scientific standing, its adherents believe that it should be taught in science classes. This applet demonstrates one of the many reasons why Behe is wrong: natural selection can easily produce systems that fit Behe’s definition of irreducible complexity. The reason is that evolution can both add and remove parts of systems. The ON nodes in the applet form the parts of a system. For this particular system to function, let’s suppose that it needs to include at least one closed shape: systems that don’t contain closed shapes don’t work. Over generations, mutation randomly turns nodes ON and OFF. In this situation, irreducibly complex systems can evolve by chance. For example, mutation could turn ON a series of nodes, forming a hexagon around a central node. If mutation then turns OFF the central node, then the system will be irreducibly complex because turning OFF any further nodes will stop the system functioning. Irreducible complexity becomes more likely if we allow natural selection to influence evolution. Let’s suppose that systems which contain larger closed shapes, and systems containing fewer ON nodes, tend to be reproduced more often. We then get steadily larger systems with fewer ON nodes evolving by natural selection. Some of these systems will be irreducibly complex – that is, if any further nodes turn OFF, the system will cease functioning. In this way, natural selection can cause irreducibly complex systems to evolve. You can read a technical report about the model here. You can read more about irreducible complexity and the ID movement here: http://www.talkorigins.org/faqs/behe.html

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