A man fires his pistol in the air during a celebratory rally after the United Nations approved a no fly zone over the country on March 18, 2011 in Tobruk, Libya. Libya declared an immediate cease-fire after the UN vote but reports indicate that Muammar Gaddafi's forces were still shelling two cities. (Photo by Joe Raedle/Getty Images)

Emily Hasler, an English Heritage employee at Charles Darwin's home, Down House, cleans a rabbit bone in his old study on April 2, 2011 in Downe, England. Staff at the house are cleaning and preparing the property ahead of their peak visitor season. The house contains the study where Darwin wrote “On the Origin of Species”, as well as family rooms and an extensive garden that inspired the renowned scientist. (Photo by Oli Scarff/Getty Images)

A rebel fighter celebrates as his comrades fire a rocket barrage toward the positions of troops loyal to Libyan ruler Muammar Gaddafi April 14, 2011 west of Ajdabiyah, Libya. Rebels exchanged artillery and rocket fire with loyalist troops west of Ajdabiyah April 14 as the confict engulfing Libya continued. (Photo by Chris Hondros/Getty Images)

Activists protest against the upcoming visit of Pope Benedict XVI on the eve of his arrival on September 21,2011 in Berlin, Germany. A variety of groups, including the poltically left-wing as well as gay and lesbian rights advocates, partook in the demonstration. The Pope is scheduled to visit Germany from September 22–25. (Photo by Sean Gallup/Getty Images)

Artist Ted Harrison makes final adjustments to his artwork created with poppies on the floor of St. Paul's Cathedral on November 10, 2011 in London, England. Mr. Harrison created the work on a 30 foot disc under the main dome of the cathedral with the intention of drawing attention to the 250,000 children worldwide currently under military orders. (Photo by Peter Macdiarmid/Getty Images)

An authenticated contemporary copy of Leonardo da Vinci's Mona Lisa on display at the Prado Museum on February 1, 2012 in Madrid, Spain. Experts of the Prado Museum say the copy was painted at the same time as the Mona Lisa in Leonardo Da Vinci's studio by one of his students.