In 1953 Crick and Watson (with some help from Rosalind Franklin) determined the structure of DNA. But despite knowing what the molecules looked like (a double helix) and what it did (encode for proteins), nobody knew how, exactly, that translating and encoding happened. There had to be, Crick had postulated, some sort "bilingual" molecule, an intermediary that could talk both to DNA and to the ribosome that created the proteins.