DNA is made up of nucleic acid bases — labelled A, C, G and T — on a backbone made of phosphates and the sugar deoxyribose. The artificial polymers, dubbed XNAs, carry the normal genetic 'alphabet' on a backbone made using different sugars.
The researchers engineered enzymes that transcribed DNA into the various XNAs, then back into new DNA strands. Faithful genetic transmission over successive DNA-to-XNA cycles allowed researchers to select for only those XNAs that attached to certain target proteins from a pool of random samples — a process akin to evolution over multiple generations (abstract).
The research confirms for the first time that replication, heredity and evolution can take place in artificial DNA-like molecules.