Fig. 18. Protein structure hypothesis. To avoid the difficulty of the sequence hypothesis described in Fig. 17, another hypothesis is presented to explain the origin of proteins. The probability of drawing any sequence, which will fold to a specified structure is fairly large. For an example of ribonuclease, it is estimated to be about 120 orders of magnitude (shaded ellipsoid) by lattice simulations. Therefore, a particular protein uses one sequence out of the enormously large number of sequences in the shaded region by chance.