1. A method of producing an antibody, in a eukaryotic cell production host; the method comprising: a. evolving a template antibody selected from an antibody library to produce a set of mutant antibodies in a eukaryotic cell production host wherein the template antibody consists of an intact immunoglobulin molecule or a fragment of an immunoglobulin molecule and has a total of n amino acid residues, said evolving comprises generating n−1 separate sets of mutant antibodies from the template antibody, each set comprising member antibodies having 19 different predetermined amino acid residues at a single predetermined position of the antibody; wherein each set of antibodies differs in the single predetermined position, and the number of different member antibodies generated is equivalent to [n−1]×19; b. confirming by sequencing a presence of the predetermined amino acid residues at the single predetermined position in each member antibody; c. screening the mutant antibodies to produce an up-mutant antibody having at least one predetermined property, characteristic or activity; and d. producing the up-mutant antibody obtained from step b. in the eukaryotic cell production host; and wherein the eukaryotic cell production host in steps (a) and (d) is the same.