Microsoft founder Bill Gates, his wife Melinda French Gates and British Prime Minister David Cameron at the World Economic Forum on January 28, 2011, in Davos, Switzerland.
Johannes Eisele/AFP/Getty Images
A Dutch man rides his bike by windmills in Kinderdijk, the Netherlands in 2007. Dutch researchers have found that the ability to ride a bike can help doctors distinguish between two similar forms of Parkinson's disease.
A boy with symptoms of cholera waits for treatment at the St. Catherine hospital in Cite Soleil in Port-au-Prince on Nov. 10, 2010. Cholera has sickened more than 91,000 Haitians and killed more than 2,000.