a, Sequences of five in-ice evolved templates (round 4) alongside template I-5. b, Extension of primer A by ribozyme tC9Y on ice-selected templates compared to favourable template I-5. (17°C, 7 days). c, Base composition of the central 36-nt evolved region of sequences from template pools over the course of selection (Positions sequenced: Starting pool = 271, Round 1 = 232, Round 2 = 582, Round 3 = 739, Round 4 = 3086). d, Ratio of the observed dinucleotide frequencies (Oi) to those expected (Ei) in the pool of round 4 sequenced templates (based on nucleotide composition). Those overrepresented are in blue, those underrepresented in red.