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PNAS July 12, 2011 vol. 108 no. 28 11320-11322
Hillis, elected to the National Academy of Sciences in 2008, has devoted his research career to phylogeny, the study of evolutionary relationships. His work tackles some of the greatest questions of evolutionary biology: How do species arise? How do genes diversify and acquire new functions? How do pathogens evolve, and how can that information be used to understand diseases? And ultimately, can we reconstruct the complete Tree of Life and use that information to help make predictions about biology?
Before the Padieu case, Hillis and colleagues had used phylogeny to determine the degree of relatedness among HIV carriers. However, in the Padieu case, prosecutors needed to show that the HIV traveled from Padieu to his victims, rather than the other way around. HIV was known to infect each host with billions of virions. However, when the virus travels from a source to recipient, a genetic bottleneck occurs and typically only one of those virions makes the jump into the new host. Because the virus evolves rapidly, Hillis’ team was able to show that six of the samples were derived from the seventh. In court, that seventh sample was revealed as belonging to Padieu ( 1).