Figure 2
From: An extension of the coevolution theory of the origin of the genetic code
Biosynthetic relationships between amino acids and their precursor non-amino acid molecules, as defined in a particular stage of the evolution of the biosynthetic pathways of amino acids. With the sole exception of proline, these are also the amino acids that first appear in a study on the temporal origin of the appearance of amino acids [54]. See Fig. 1 for further information.