One of the most powerful evidences for evolution are the similarities between species. The reason why the similarities are such powerful evidence is that a great variety of designs are possible. A wise designer certainly would make use of this great variety of possible designs but common descent is restricted to whatever is available. Consider, for example, the pentadactyl structure—five digits (four fingers and a thumb for humans) at the end of the limb structure—which is found throughout the tetrapods. The activities of this massive group of fauna include flying, grasping, climbing and crawling. Such diverse activities, evolutionists reason, should require diverse limbs. There seems to be no reason why all should need a five digit limb. Why not three digits for some, eight for others, 13 for some others, and so forth? And yet they all are endowed with five digits. Their shapes and sizes vary greatly, but nonetheless there are five digits. Obviously the pentadactyl structure must be an artefact of common descent—a suboptimal design that was handed down from a common ancestor rather than specifically designed for each species. A key premise of this argument is that a tremendous variety of designs is possible. Read more