text: The technique works backwards from the target to identify a precursor molecule and an enzyme that converts it into the target, and then a second precursor that can produce the first and so on until a simple, inexpensive molecule becomes the beginning of the series. For each precursor, the enzyme is evolved using induced mutations and natural selection to produce a more productive version. The evolutionary process can be repeated over multiple generations until acceptable productivity is achieved. The process does not require high temperature, high pressure, the use of exotic catalysts or other elements that can increase costs. The enzyme "optimizations" that increase the production of one precursor from another are cumulative in that the same precursor productivity improvements can potentially be leveraged across multiple target molecules.