Frances Arnold is the Dick and Barbara Dickinson professor of chemical engineering and biochemistry at California Institute of Technology, Pasadena, US. Her work focuses on elucidating the principles of biological design using laboratory evolution experiments.

What inspired you to become a scientist?
I wasn't sure I wanted to become a scientist until I actually became one. I was always good at math and science and that was the easiest way for me to get into Princeton University (US). I did mechanical and aerospace engineering, which had the fewest requirements, but I always thought I'd be a diplomat or perhaps the CEO of a corporation. I had no thought that I'd become a scientist, because I was far more interested in economics and languages. But after college I started working as an engineer in Brazil and at the Solar Energy Research Institute in Colorado (under President Carter, who believed that alternative energy research was important) and found that I enjoyed it.  It wasn't until I went to graduate school to get a PhD in chemical engineering, however, that I realised how much I loved biochemistry and that I could have a marvelous career in research.

Darwin's view of evolution describes mutation and natural selection over millions of years.  How can you study evolution in the lab in such reduced timeframes?
What we do is not exactly like natural evolution - it's actually artificial selection. Even Darwin (see portrait below) recognised that under strong selection pressure, such as what you impose during plant and animal breeding, large phenotypic changes can manifest themselves very quickly, in just a few generations. I do the same thing, but with molecules, and call it directed evolution. We mutate or recombine genes to create genetic diversity and clone the altered genes into plasmids for expression in a host organism.  We screen the mutants for properties of interest, isolate the improved genes, and repeat the cycle until we have bred the molecule(s) we want.

What are you working on at the moment?
I'm interested in engineering new enzymes for bioenergy and 'green' chemistry.  Nature is a very good chemist, but there is still room for improvement. For example, cellulases are the enzymes that degrade cellulose into sugars.  Cellulose is a very abundant source of sugar but it is really difficult and costly to extract the sugar from it for renewable fuels or chemicals. We need much better enzymes than the ones we find in nature, and I have some ideas for creating those in the laboratory. I'm also interested in what laboratory evolutionary experiments tell us about how natural evolution might have occurred, how things evolved in the natural world.

You construct synthetic enzymes.  If you could make a synthetic human, what new improved feature would you try to engineer and why?
Greater wisdom, for obvious reasons.

What is your greatest achievement so far?
I think that this must be helping to educate the brilliant students and postdocs who come to the California Institute of Technology. I've been there for 24 years and I've had the pleasure of interacting with well over 100 of some of the smartest young scientists and engineers in the world. If I can help inspire them to use their remarkable brains to solve important problems, and enjoy the process, I feel I have done something really useful.

How has the global recession affected science?
Personally, I have not really suffered. I've never had much trouble getting funding. But I do see that the recession has limited the job market for graduates. The opportunities for young people are fewer now, in industry as well as in academic research. I hope that does not dampen their enthusiasm for tackling the most important problems.

You travel the world attending conferences.  Which destination is your favourite?
I love the whole world - I can't choose a favourite. Five years ago, I took all three of my sons around the world for a whole year. They went to school in Australia, Africa, and Wales that year. I love to go to new places, and find that almost every place has something wonderful to offer.

What do you do in your spare time?
I have three sons, whom I adore.  I enjoy doing things and traveling with them. Scuba diving and yoga are great.  I also have a rustic (no water, no electricity) cabin in the mountains where I go to relax or work. I am deeply concerned about climate change and renewable energy and spend considerable time outside of my research on these issues.

What would you be if you weren't a scientist?
I would love to be a musician and composer, but sadly don't have any real talent for it. 

For which scientific discovery would you like to have been responsible?
The theory of natural selection, of course!