In the light of evolution III: two centuries of Darwin.

C harles Darwin’s enthusiasm and expertise in natural history contributed hugely to his elucidation of evolution by natural selection, which stands as one of the grandest intellectual achievements in the history of science. Darwin was a lifelong observer of nature, stating in correspondence that some of his happiest times in youth were spent fishing on rainy days and ‘‘entomologizing’’ when England’s weather was nice. At the age of 22, he boarded the HSM Beagle for a 5-year stint as Captain Fitzroy’s traveling companion and the ship’s naturalist, an appointment that introduced him to biodiversity on a global geographic scale. Darwin’s breadth and depth of naturalhistory experience would later be on full display in his most defining scientific works (3–5) in his detailed treatises on orchids, insectivorous plants, coral reefs, barnacles, and earthworms (6–10). The year 2009 marks the 200th anniversary of Charles Darwin’s birth and the 150th anniversary of his most influential publication (3). Darwin transformed the biological sciences in much the same way that Nicolaus Copernicus, Galileo Galilei, and Isaac Newton, centuries earlier, transformed the physical sciences—by demonstrating that the universe operates according to natural laws that fall within the purview of rational scientific inquiry. In 1543, Copernicus published De revolutionibus orbium celestium (‘‘On the Revolutions of the Celestial Spheres’’) that challenged conventional wisdom that the Earth was the center of Creation, and instead promoted the idea that natural laws govern the 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. Before Darwin, most scientists and 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 in the 5th century B.C. (see ref. 11), and it was expressed again in a thoughtful and elegant treatise (Natural Theology) published in 1802 by the Reverend William Paley (12). Darwin later recalls in his autobiography (13) 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. In the articles of this Colloquium, leading evolutionary biologists and science historians reflect on and commemorate the Darwinian Revolution. The authors of these Proceedings canvass modern research approaches and current scientific thought on each of the 3 main categories of selection (natural, artificial, and sexual) that Darwin addressed during his career. Although his legacy is associated primarily with the illumination of natural selection in The Origin, Darwin also contemplated and wrote extensively about what we would now term artificial selection and sexual selection, as reflected for example in two books titled, respectively, The Variation of Animals and Plants Under Domestication (1869) and The Descent of Man and Selection in Relation to Sex (1871). In a concluding section of these Proceedings, several science historians comment on Darwin’s seminal contributions. Thus, these Proceedings are organized in 4 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.