“I realized that the way most people were going about protein engineering was doomed failure,” Dr. Arnold said. “To me it is obvious that this is the way it should be done.”

She tried to change an enzyme called subtilisin. She wanted it to accelerate change in an organic solvent, so she created random mutations in the enzyme’s genetic code and introduced the mutated genes to bacteria that then created different types of subtilisin.

Dr. Arnold selected the type of subtilisin that performed the best. Once she found the best variant of subtilisin, she continued to mutate it until she had the very best version.

With this directed evolution, she could show the power behind allowing chance and directed selection instead of depending on human logic and understanding of how genes and enzymes are supposed to work. This was the initial step toward the revolution in enzyme mutation.

When she began her new approach, “some people looked down their noses at it,” Dr. Arnold told the National Science and Technology Medals Foundation. “They might say ‘It’s not science’ or that ‘Gentlemen don’t do random mutagenesis.’ But I’m not a scientist, and I’m not a gentleman, so it didn’t bother me at all. I laughed all the way to the bank, because it works.”

Now, Dr. Arnold said, these are some of the questions she would like to answer: “How do you evolve innovation? How do you get a whole new chemical activity that you don’t know already existed? How can I evolve a whole new species of enzymes?”