Just a hundred years ago, in 1899, the noted German biologist Ernst Haeckel published a book called The Riddle of the Universe. In it he reviewed what he believed to be the most significant scientific achievements of the nineteenth century and considered their impact on the relationship between science and religion. Among his other achieve-ments it was Haeckel who, in an earlier work, introduced the term ‘ecology’ to describe the study of organisms in relation to where they live. To mark the centenary of the publication of Haeckel’s book it seems appropriate to take a look at the world through the eyes of the founder of scientific ecology and to compare this with the developments of the twentieth century.