motion of physical objects in the universe. In 1859, in On the Origin of Species, Darwin developed the equally revolutionary concept that a natural but nonrandom process—natural selection—yields biological adaptations that otherwise can give the superficial impression of direct intelligent craftsmanship.

Darwin’s impacts have been felt far beyond science. Prior to Darwin, most scientists as well as theologians accepted what seemed obvious: that divine intervention must have underlain nature’s design. The traditional “argument from design” traces back at least to the classical Greek philosopher Socrates more than 400 B.C. [see Sedley (2008)], and it was expressed again in a thoughtful and elegant treatise (Natural Theology) published by the Reverend William Paley (1802). Darwin later recalls in his autobiography [see Barlow (1958)] that Paley’s logic “gave me as much delight as did Euclid” and that it was the “part of the Academical Course [at the University of Cambridge] which … was the most use to me in the education of my mind.” Darwin was still a natural theologian when he boarded the Beagle in 1831 on what would become a fateful voyage, for Darwin and for humanity, into uncharted philosophical (as well as scientific) waters.

This book is the outgrowth of the Arthur M. Sackler Colloquium “Two Centuries of Darwin,” which was sponsored by the National Academy of Sciences on January 16–17, 2009, at the Academy’s Arnold and Mabel Beckman Center in Irvine, California. It is the third in a series of colloquia under the umbrella title “In the Light of Evolution.” The first book in this series was titled In the Light of Evolution, Volume I: Adaptation and Complex Design (Avise and Ayala, 2007). The second was In the Light of Evolution, Volume II: Biodiversity and Extinction (Avise et al., 2008).

In the chapters of this book, leading evolutionary biologists and science historians reflect upon and commemorate the Darwinian Revolution. They canvass modern research approaches and current scientific thought on each of the three main categories of selection (natural, artificial, and sexual) that Darwin addressed during his career. Although Darwin’s legacy is associated primarily with the illumination of natural selection in The Origin, he also contemplated and wrote extensively about what we now term artificial selection and sexual selection, as reflected for example in two books titled, respectively, The Variation of Animals and Plants Under Domestication (1868) and The Descent of Man and Selection in Relation to Sex (1871/1959). In a concluding section of this book, several science historians comment on Darwin’s seminal contributions. Thus, this book is organized in four parts: Natural Selection, or Adaptation to Nature; Artificial Selection, or Adaptation to Human Demands; Sexual Selection, or Adaptation to Mating Demands; and The Darwinian Legacy, 150 Years Later.