In 1990, two labs independently developed the technique of selection: the Gold lab, using the term SELEX for their process of selecting RNA ligands against T4 DNA polymerase; and the Szostak lab, coining the term "in vitro selection", selecting RNA ligands against various organic dyes. The Szostak lab also coined the term aptamer (from the Latin, "apto", meaning 'to fit') for these nucleic acid-based ligands. Two years later, the Szostak lab and Gilead Sciences, independent of one another, used "in vitro selection" schemes to evolve single stranded DNA ligands for organic dyes and human coagulant, thrombin (see anti-thrombin aptamers), respectively. There does not appear to be any systematic differences between RNA and DNA aptamers, save the greater intrinsic chemical stability of DNA.