“The Challenge!” Young boy relishes in a game of tug of war before school. Photo location: Lake Titicaca, Peru. (Photo and caption by Paul Heyman/National Geographic Photo Contest)

Aiden Haas, left, and Lilli Alcala pose after being crowned Mud King and Mud Queen at the 29th annual Mud Day, Tuesday, July 12, 2016 in Westland, Mich. The event, open to children 12 and younger, was at the Hines Park-Nankin Mills Area west of Detroit. Children 12 and younger were able to slosh around in the pit while participating in mud limbo, wheelbarrow races and other free activities. (Photo by Carlos Osorio/AP Photo)

Indian models showcase creations by designer Shivan & Naresh during the Lakme Fashion Week (LFW) Winter/Festive 2016 in Mumbai on August 27, 2016. (Photo by Sujit Jaiswal/AFP Photo)

American Paralympic snowboarder Amy Purdy dances with a robot during the opening ceremony of the Rio 2016 Paralympic Games at the Maracana stadium in Rio de Janeiro on September 7, 2016. (Photo by Yasuyoshi Chiba/AFP Photo)

Austrian alpine skiers (LtoR) Georg Streitberger, Klaus Kroell, Max Franz, Joachim Puchner, Romed Baumann pose in the Olympic Rings on February 4, 2014 at the Mountain Olympic Village at the Rosa Khutor Alpine centre, four days prior to the start of the 2014 Sochi Winter Olympic Games. (Photo by Fabrice Coffrini/AFP Photo)

The 100-metre (300-foot), sword-wielding statue of “The Motherland” is seen in the National Museum of the History of the Great Patriotic War in Kiev March 17, 2014. On a blustery day on the banks of the Dnieper, the statue of “The Motherland”, a Soviet hammer and sickle on her shield, towered overhead, a reminder of the common cause Ukrainians and Russians died for side by side in their millions in World War Two and which Russian President Vladimir Putin thinks Ukraine has betrayed by turning to “fascism” and the West. (Photo by Konstantin Grishin/Reuters)

Hot air balloons fly over the sky in Chiang Mai province, northern Thailand, December 6, 2014. The two-day International Balloon festival 2014 featuring balloon pilots from Germany, Spain, Netherlands, Britain, and Czech Republic is held on December 06-07 2014 to celebrate Thai King Bhumibol Adulyadej's 87th birthday and also aimed to promote the tourism industry in Chiang Mai northern city. (Photo by Pongmanat Tasiri/EPA)

A weeping South Vietnamese mother and her three children are shown on the deck of this amphibious command ship being plucked out of Saigon by U.S. Marine helicopters in Vietnam, April 29, 1975. (Photo by AP Photo)