The California Academy of Sciences is a natural history museum in San Francisco, California, that is among the largest museums of natural history in the world, housing over 26 million specimens. The Academy began in 1853 as a learned society and still carries out a large amount of original research, with exhibits and education becoming significant endeavors of the museum during the 20th century. Completely rebuilt in 2008, the building covers 400,000 square feet (37,000 square metres) and is among the newest natural history museums in the United States. The primary building in Golden Gate Park reopened on September 27, 2008. The California Academy of Sciences, Californias oldest operating museum and research institution for the natural sciences, is governed by a forty-one member Board of Trustees who are nominated and chosen by the Academy Fellows. The Academy Fellows are, in turn, "[n]ominated by their colleagues and appointed by the Board of Trustees...the Fellows remain members of the Fellowship for life." The Board of Trustees are then responsible for appointing the executive management of the Academy, who in turn are responsible for overseeing the Academys overall operation and the hiring of its other managers and employees.