Analysis of a newly-identified 48-year-old tissue sample from a woman infected with linkurl:HIV; has confirmed that the virus emerged in the early 20th century, researchers report today in Nature. By comparing the differences between the sequence of this sample from 1960, the second-oldest ever found, and that of a 1959 sample identified a decade ago, linkurl:Michael Worobey; of the University of Arizona and colleagues were able to calibrate the molecular clock of HIV. "I think that improved the dating of the epidemic, and moved it back by a couple of decades," he said. Also, he noted, having two samples from so far back has opened the door to detailed studies of the virus's molecular evolution. "We could make inferences before this point," he said, "but until you really see it you're going on assumption rather than direct evidence." Based on analysis of the 1959 sample, first analyzed by David Ho's...

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