The present invention relates to a method for 
in vitro creation of molecular libraries evolution of 
protein function. Particularly, it relates to variability and modification of 
protein function by 
shuffling polynucleotide sequence segments. A 
protein of desired characteristics can be obtained by incorporating variant 
peptide regions (variant motifs) into defined 
peptide regions (
scaffold sequence). The variant motifs can be obtained from parent 
DNA which has been subjected to 
mutagenesis to create a plurality of differently mutated derivatives thereof or they can be obtained from 
in vivo sequences. These variant motifs can then be incorporated into a 
scaffold sequence and the resulting coded protein screened for desired characteristics. This method is ideally used for obtaining antibodies with desired characteristics by isolating individual CDR 
DNA sequences and incorporating them into a 
scaffold which may, for example, be from a totally different 
antibody.