The invention relates to the production of variants of a protein in an in vitro evolution method, comprising the steps: (A) preparing an in vitro expression system, comprising: (i) a nucleic acid sequence S, which codes for a protein Y to be varied; (ii) a target molecule X 1 capable of binding to protein Y and/or at least one variant Y thereof; (iii) an RNA polymerase (Pol) capable of transcribing the nucleic acid sequence S; (iv) a reverse transcriptase (RT) capable of reverse transcribing transcripts of nucleic acid sequence S, the target molecule X being coupled to Pol and protein Y to RT, or target molecule X being coupled to RT and protein Y being coupled to Pol; (B) incubating the in vitro expression system from (A) under conditions that enable a transcription, a reverse transcription and a translation while forming variants Y' of protein Y and nucleic acid sequences S' coding therefor, and which promote the formation of variants Y' with improved binding properties for target molecule X; (C) isolating and optionally characterizing those variants Y' that have improved binding properties for binding to X and/or isolation nucleic acid sequence variants S' that code for Y'.