 Similar functions are carried out by the same sequence of reactions that appear in all organisms for essential chemical operations (some variations exist that consist of new utilizations of universal metabolic sequences).On page 104 Monod states "The fundamental biological invariant is DNA.That is why Mendel's definition of the gene as the unvarying bearer of hereditary traits, its chemical identification by Avery (confirmed by Hershey), and the elucidation by Watson and Crick of the structural basis of its replicative invariance, without any doubt constitute the most important discoveries ever made in biology."