There are two contrasting ideas about the pace of evolution. One holds that evolution is gradual a progression of slow steady change. The other sees it as long periods of inactivity, interspersed with bouts of rapid change. These two diagrams show the essential differences between the two concepts. In each, the progression of evolutionary change is visualized as a rolling wheel. The track left behind is the evolutionary history of that wheel. The lower wheel, illustrating the gradualist theory, is made up of many tiny facets. Each of these represents a single mutation, which in turn produces an adaptation. This wheel rolls gradually and smoothly by the accumulation of these small mutational changes.