(or even likely) before the emergence of canonical AAs like arginine or lysine, although eventually lysine and arginine would have replaced ornithine in biology. Finally, while aromatic AAs are limited in number within IDPs, their role in the functionality and phase separation of modern IDPs cannot be ignored. For example, weak non-covalent interactions (cation-π and sp2/π) between tyrosine and arginine residues within an IDP can result in phase separation; induced mutations of tyrosine residues within the IDPs have been shown to affect this ability. Such weak interactions are also required for a synthetic mimic of FUS protein and RGG domains of LAF-1 to phase separate in vitro. Tyrosine and histidine interactions have also been shown to be important for phase separation, while hydrophobic interactions of phenylalanine can strengthen charge-charge intermolecular interactions that result in phase separation as well. In particular, phenylalanine present in FF dipeptide motifs can produce amyloid-like hydrophobic supramolecular assemblies. A recently published study involving aromatic dipeptides joined by hydrophilic AAs that formed coacervates has even demonstrated an increase in the rate of reactions that are prebiotically relevant. However, unlike in modern LLPS systems, the role of aromatic hydrophobic AAs in primitive coacervate formation remains to be explored in-depth. One reason may be that aromatic AAs evolved later than other AAs, and so aromatic residues have rarely been a part of primitive coacervates, potentially leading some primitive coacervate researchers to eschew the inclusion of large amounts of aromatic residues in their systems. However, recent research has pointed to the fact that basic AA residues may have been incorporated into primitive peptides much later than initially thought. This suggests that the role of aromatic AAs and their interactions with other AAs that contribute to primitive phase separation warrants further investigation.