Doctors at a hospital in Aleppo, Syria, treat a boy injured in what the government said was a chemical weapons attack on March 19. Syria's government and rebels accused each other of firing a rocket loaded with chemical agents outside of Aleppo. George Ourfalian/Reuters/Landov hide caption

itoggle caption George Ourfalian/Reuters/Landov

The research of British naturalist Alfred Russel Wallace (1823-1913) played a pivotal role in developing the theory of natural selection. But over time, Charles Darwin became almost universally thought of as the father of evolution. Hulton-Deutsch Collection/Corbis hide caption

itoggle caption Hulton-Deutsch Collection/Corbis

A mammoth spinning vortex is seen on Saturn, in this "false-color" photograph released by NASA Monday. The image was captured by the Cassini spacecraft. A related image, presenting what a human eye would see, is farther down this page. NASA hide caption

itoggle caption NASA

Beekeepers demonstrate at the EU headquarters in Brussels Monday, as lawmakers vote on whether to ban pesticides blamed for killing bees. Georges Gobet/AFP/Getty Images hide caption

itoggle caption Georges Gobet/AFP/Getty Images

A phonorecord by Alexander Graham Bell, one of the Smithsonian's trove of recordings left there by the inventor of the telephone. Richard Strauss/Smithsonian's National Museum of American History Via AP hide caption

itoggle caption Richard Strauss/Smithsonian's National Museum of American History Via AP

A miniature ninja throwing star or a surgical device? The microgripper, shown here coming out of a catheter tube, is activated by body heat. The sharp appendages fold up when the device warms up. Evin Gultepe, Gracias Lab, Johns Hopkins University. hide caption

itoggle caption Evin Gultepe, Gracias Lab, Johns Hopkins University.