1. A diversity generation device comprising: a fragmentation module configured to fragment parental nucleic acids to produce nucleic acid fragments; and a programmed thermocycler operably coupled to the fragmentation module and configured to receive the nucleic acid fragments from the fragmentation module and to reassemble the nucleic acid fragments to produce shuffled nucleic acids, wherein the programmed thermocycler comprises a thermocycler operably coupled to a computer, wherein the computer comprises one or more instruction sets for: calculating one or more crossover regions between two or more parental nucleic acid sequences of the parental nucleic acids; using the calculated one or more crossover regions to select the parental nucleic acids for use in the fragmentation module; and calculating an amount of uracil and an amount of thymidine based on a desired fragment size.