5' phosphates hard to make. RNA as the original biopolymer Ability to self replicate. Ability to perform catalytic functions. Ability to catalyze peptidyl transfer. 2'-OH is very reactive, causing degradation of polymer.
Nucleotides are hard to make.
5' phosphates hard to make. GC base pairing and AU base pairing is simple and plausible Problem lies in the backbone. Fidelity is very important. If next-generation biopolymers are unable to facilitate self replication the advantage is lost. Variation is important.