Isn't Evolution Improbable?

In this unit students can learn: about the long time scales that are involved in understanding the evolution of species by natural selection; that very complex organs develop slowly over time through a series of small changes; that the evolution of the eye can seem very improbable, but an understanding of the long timescale involved in evolution and the way it operates illustrates how it has happened and how other complex organs have evolved; the different ways in which the theory of evolution is supported by evidence.