Shoppers crowd a narrow street outside Tsukiji market in Tokyo on Dec. 31, 2010. Japan has relatively tight social rules. And that makes sense, according to researchers. When people are squeezed together, they have an incentive to cooperate. Toru Yamanaka/AFP/Getty Images hide caption

itoggle caption Toru Yamanaka/AFP/Getty Images

A worker checks the status of the water level at the Unit 1 reactor at the Fukushima Dai-ichi nuclear power plant in Japan on Tuesday. Japanese officials said the reactor doesn't appear to be holding water, which means its core probably sustained more damage than originally thought. TEPCO/AP hide caption

itoggle caption TEPCO/AP

Two cells — one marked mostly in green, the other in blue — of a newly discovered organism found in water samples collected from the University of Exeter pond. Scientists think these "cryptomycota" use their tails to propel themselves while searching for food. Meredith Jones/Nature hide caption

itoggle caption Meredith Jones/Nature

A Chinese farmer sweeps up dried cobs and stripped corn on a roadside outside Beijing. A new study finds that global production of corn and wheat would have been 5 percent higher if not for global warming. Alexander F. Yuan/AP hide caption

itoggle caption Alexander F. Yuan/AP

Alligator River National Wildlife Refuge is a low-lying area made of 154,000 acres of marshland and forest on the eastern shore of North Carolina. Much of the land is susceptible to sea level rise, so conservation managers are taking steps to help slow the inevitable. U.S. Fish and Wildlife Service hide caption

itoggle caption U.S. Fish and Wildlife Service

Workers at the Fukushima Dai-ichi nuclear power plant spray a substance to help reduce dust on April 1. The cleanup operation at the facility could take more than a decade. TEPCO hide caption

itoggle caption TEPCO

Keiji Nagashima has been farming spinach in Ibaraki prefecture for 25 years but will be destroying this year's crop because of fears of radiation exposure. "I can't have a life without the spinach," he says. Richard Harris/NPR hide caption

itoggle caption Richard Harris/NPR