"It is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting upon us."

So concludes Charles Darwin's On the Origin of Species, the book whose publication in 1859 rocked the scientific world with its theory of evolution and challenged humankind's prevailing notion of its place in the natural order. Controversial in its day, Darwin's treatise introduced readers to such concepts as "the struggle for existence" and "natural selection," and provided them with an understanding of the interdependence of species. The text of this volume is taken from the first edition, in which Darwin made his argument most forcefully.