Given the following passage  "Raymond B. Bragg, the associate editor of The New Humanist, sought to consolidate the input of Leon Milton Birkhead, Charles Francis Potter, and several members of the Western Unitarian Conference. Bragg asked Roy Wood Sellars to draft a document based on this information which resulted in the publication of the Humanist Manifesto in 1933. Potter's book and the Manifesto became the cornerstones of modern humanism, the latter declaring a new religion by saying, "any religion that can hope to be a synthesising and dynamic force for today must be shaped for the needs of this age. To establish such a religion is a major necessity of the present." It then presented 15 theses of humanism as foundational principles for this new religion.",  answer the following question. Note that the answer is present within the text.  Question: What was the Humanist Manifesto based on?
document