"INTELLIGENT DESIGN," IRREDUCIBLE COMPLEXITY AND THE FOSSIL RECORD

One of the primary arguments made against evolutionary theory by advocates of Intelligent Design (ID) is based on their concept of “irreducible complexity.” Irreducible complexity is defined by them as a multi-component system of interacting parts that contribute to a basic function, and where the removal of any one part will cause the system to effectively cease functioning. Advocates of ID argue that such systems could not be assembled through gradual evolutionary pathways. Many anatomical systems and structures are irreducibly complex by this definition, and yet the fossil record provides a window into the steps by which such structures were assembled. We are in many cases not left to mere speculation about the anatomical steps actually taken from one state to another. The fossil record provides examples of how complex structures with novel functions can be derived from preexisting structures with other functions. It also shows the evolution of structures with specialized functions from those with multiple suboptimal functions. Structures also evolve as integrated units and do not pass through any non-adaptive state. Examples from the fossil record of the evolutionary origin of integrated multicomponent anatomical systems include: 1) the mammalian middle ear, 2) the avian wing, and 3) the arthropod skeletal/muscular system.