Fig. 19. GNC-, SNS-, and GC-NSF(a)-0th-order structure hypotheses on the origin of proteins. (A) According to the 0th-order hypothesis, extant proteins should be originated from a smaller number of random sequences (closed circles) specified by particular amino acid compositions, which are determined by the GNC- and SNS primitive genetic codes. At present, newly-born proteins could be derived from proteins encoded by ancestral GC-NSF(a) genes (shaded ellipsoid), the modified form of SNS repeating sequences, (SNS)n. (B) It is generally considered that a tertiary structure or a higher-order structure of a protein is determined by a primary structure, or an amino acid sequence, which is determined by one-dimensional genetic information on DNA. Contrary to that, we provided another hypothesis on formation of globular proteins, in which primary structure is restricted by specific amino acid compositions, such as GNC- , SNS-0th-order structures and its modified form of GC-NSF(a)-0th-order structure (Fig. 19(A)). First genes determining amino acid sequences (the primary structure) of proteins realize the 0th-order structure of newly-born proteins through creative processes of newly-born genes.