In this episode I talk with Paul Turner, an associate professor of ecology and evolutionary biology at Yale University.2009 saw the emergence of a new strain of H1N1 flu. Scientists soon determined that the virus had leaped from pigs to humans and then spread to millions of people. When viruses make this kind of leap it's a reason to worry. In 1918 when a strain of flu leapt from birds to humans, 50 million people died in a matter of months. So far the new H1N1 flu strain is behaving like a relatively ordinary flu. Still even ordinary flu is a matter of serious concern. Over 4,000 people in the US alone have died from the new H1N1 flu strain and scientists can't say for sure what it would take to turn this new strain into a global killer.It's a sobering reminder of how mysterious virus evolution remains. Over the past century a number of viruses have made the leap from animal host to humans including SARS and HIV and scientists worry that the next great plague may be a virus that we don't even know about yet.Paul Turner is learning how new viruses emerge by watching them evolve in his lab. Fortunately the viruses he studies don't make you sick. Instead they attack E-coli and other single celled hosts. But these viruses are teaching Turner and his colleagues about some of the fundamental rules that govern how viruses evolve to attack new hosts. Turner hopes that what he and his colleagues learn about those rules may help future generations of scientists fight against the next generation of viruses that can make us sick.