Mara Salvatrucha (MS) gang members show off their weapons in the Las Victorias district of San Salvador. In March 2012, the two largest gangs in El Salvador - the Mara Salvatrucha (MS) and the Barrio 18 (M18) - agreed on a truce following secret negotiations between gang leaders in prison which were mediated by a bishop and a former rebel leader. It is unclear whether the decision was the idea of the gangs themselves or whether they were encouraged by the government. (Photo by Adam Hinton)

A baby rhesus macaque (Macaca mulatta) looks up as it plays with a tiger cub at a zoo in Hefei, Anhui province, August 2, 2012. (Photo by Jianan Yu/Reuters)

“Red Land: Sunset Cloud Village is one of the most picturesque places in Red Land, China. As its name indicates, it's best to see before sunset. The reddish brown soil turns redder after rainfall and after farmers plow the land”. (Photo and comment by Peng Jiang/National Geographic Photo Contest via The Atlantic)

Mystical Forest. Tracey Jennings photographed this seven-gill shark in a kelp forest just off the shore of Simon's Town near Cape Town, South Africa. You don't need to travel far from cities to visit Narnia. This 7 gill shark was photographed in a kelp forest just off the shore of Simonstown near Cape Town, South Africa. (Photo by Tracey Jennings/National Geographic Travel Photographer of the Year Contest)

Tomomi Ota visits a local shrine with her humanoid robot Pepper in Tokyo, Japan, 26 June 2016. Reaching 120cm in height and 28 kilograms in weight, Pepper does not enter in the category of portable robot. But those characteristics dont stop Tomomi Ota to take Pepper in a cart to stroll in her neighborhood, go shopping or even take the subway... (Photo by Franck Robichon/EPA)

Sete Tamang, 20, avalanche survivor, waits to receive the bodies of his colleagues outside a morgue at Teaching Hospital in Katmandu, Nepal, Monday, October 20, 2014. Nepal was wrapping up rescue operations in its northern mountains Monday, saying all the hikers believed to have been stranded on a trekking route by a series of deadly blizzards are now safe. (Photo by Niranjan Shrestha/AP Photo)

In this July 12, 2007 file photo, a two-day-old piping plover runs along a beach in the Quonochontaug Conservation Area in Westerly, R.I. (Photo by Steven Senne/AP Photo)

Mohammad, a 13-year-old fighter from the “Free Syrian Army”, plays with a cat in Aleppo's Bustan al-Basha district, Syria October 28, 2013. Mohammad joined the Free Syrian Army after his father died during clashes with the Syrian regime. The gun he is using was his father's. (Photo by Molhem Barakat/Reuters)