You cannot make complex, efficient working objects, like the human eye or the wings of an eagle, in a single step. It would be like getting from the bottom of a mountain to the top in a single leap - highly improbable. The third part of the Christmas Lectures demonstrates this fact, and illustrates how evolution from simplicity to complexity takes place across all life in the natural world gradually, inch by inch, up Mount Improbable. From stick insects, to squid, to owls, the marvelous development of DNA to survive and thrive through natural selection is undeniable.