A lab worker exposes his arm to Aedes aegypti mosquitoes, which transmit Zika virus, during testing in the lab at Roosevelt Hospital in Guatemala City, Guatemala. Saul Martinez/Bloomberg via Getty Images hide caption

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While some scientists seek ways to stop the spread of Zika by mosquitoes, others have received new funding from the National Institutes of Health to track the genes and habits of the virus itself. Felipe Dana/AP hide caption

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Emotion seemed to fuel plenty of sighs by Humphrey Bogart's character Rick (right) in the 1942 film classic Casablanca, and even Rick's good friend Sam, played by actor Dooley Wilson, couldn't console him. Archive Photos/Getty Images hide caption

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December brought storm clouds to the Porter Ranch neighborhood in Southern California's San Fernando Valley. David McNew/AFP/Getty Images hide caption

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Criminologist Joseph Richardson is skeptical that the federal government alone can solve the data problem for police shootings. "There has to be a more pioneering, innovative approach to doing it," he says. Spotmatik/iStockphoto hide caption

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Sylvester Williams, a Denver Broncos nose guard, nabs Isaiah Crowell of the Cleveland Browns last October. If measured by BMI, Williams is obese. AAron Ontiveroz/Denver Post via Getty Images hide caption

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When so-called senescent cells were removed from mice, they were healthier and lived longer than mice that still had the cells. Philippe Merle/AFP/Getty Images hide caption

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Scientists have the ability to use DNA from three adults to make one embryo. But should they? A. Dudzinski/Science Source hide caption

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A Chipotle Mexican Grill employee prepares a burrito for a customer in Seattle. The CDC believes the two recent E. coli outbreaks at Chipotle restaurants are over. Stephen Brashear/AP hide caption

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