In the light of evolution III: Two centuries of Darwin

This paper serves as an introduction to this PNAS supplement, which resulted from the Arthur M. Sackler Colloquium of the National Academy of Sciences, ''In the Light of Evolution III: Two Centuries of Darwin,'' held January 16 -17, 2009, at the Arnold and Mabel Beckman Center of the National Academies of Sciences and Engineering in Irvine, CA.It is the third in a series of colloquia under the general title ''In the Light of Evolution'' (ILE; and see Box 1).The complete program and audio files of most presentations are available on the NAS web site at www.nasonline.org/ SacklerDarwin.Papers from the first two colloquia in the ILE series, titled ''Adaptation and Complex Design'' and ''Biodiversity and Extinction,'' appeared in refs. 1 and 2, respectively.