A soldier with the U.S. Army's 3rd Infantry Division on March 20, 2003, among the first troops to set foot in Iraq in that year's invasion. David P. Gilkey /Detroit Free Press/MCT hide caption

itoggle caption David P. Gilkey /Detroit Free Press/MCT

Leap into the Void, 1960 (Yves Klein, Harry Shunk and Jean Kender) The Metropolitan Museum of Art/Courtesy of the National Gallery of Art hide caption

itoggle caption The Metropolitan Museum of Art/Courtesy of the National Gallery of Art

The bucardo, or Pyrenean ibex, lived high in the Pyrenees until its extinction in 2000. Three years later, researchers attempted to clone Celia, the last bucardo. The clone died minutes after birth. Taxidermic specimen, Regional Government of Aragon, Spain Robb Kendrick/National Geographic hide caption

itoggle caption Robb Kendrick/National Geographic