Selective breeding is the cause of that. Particularly, peacocks with large tails are forced to mate together to produce offspring with large tails. from the offrspring the ones with the largest tail are chose again and they mate. This process goes on until we have a fair amount of the animal with the desirable characteristics
Isolate plasmids from bacteria the select the part of DNA that codes for the production of insuline. then using a restriction enzyme cut open thhe plasmid using same restriction enzyme cut part of the DNA then using DNA ligase jion the cut end of DNA ro plasmid to form recombinant plasmids. the incubate the recombinant plasmids with plasmid removed bacteria. some bacteria take up the recombinat plasmid and produce insuline.