Before the advent of genetic engineering, insulin was obtained from the pancreas of pigs and cows.

This method had several drawbacks:

* Limited supply: The amount of insulin obtainable from animal sources was limited, which made it difficult to meet the needs of all diabetic patients.

* Allergic reactions: Some people were allergic to animal insulin, leading to side effects.

* Ethical concerns: The use of animal pancreases raised ethical concerns about animal welfare.

The development of genetically engineered bacteria and yeast for insulin production revolutionized the treatment of diabetes by providing a safe, abundant, and more affordable source of the hormone.