Crick develops from the mid-1950s onward the sequence hypothesis: the order of bases in DNA encodes the order of amino acids in a protein. He formulates it in his paper "On Protein Synthesis" (1958), directly inspired by Sanger's demonstration that insulin has a fixed, determined amino acid sequence, not an amorphous structure as had been assumed until then. It lays the conceptual foundations of what would later be formalized as the central dogma of molecular biology.