Book excerpt: The letters in this volume cover two of the most momentous years in Darwin's life. Begun in 1856 and the fruit of twenty years of study and reflection, Darwin's manuscript on the species question was a little more than half finished, and at least two years from publication, when in June 1858 Darwin unexpectedly received a letter and a manuscript from Alfred Russel Wallace indicating that he too had independently formulated a theory of natural selection. The letters detail the various stages in the preparation of what was to become one of the world's most famous works: Darwin's On the Origin of Species by Means of Natural Selection, published by John Murray in November 1859. They reveal the first impressions of Darwin's book given by his most trusted confidants, and they relate Darwin's anxious response to the early reception of his theory by friends, family members, and prominent naturalists. This volume provides the capstone to Darwin's remarkable efforts for more than two decades to solve one of nature's greatest riddles - the origin of species.