An alligator named Muja is seen in its enclosure in Belgrade's Zoo, Serbia, August 14, 2018. Muja is officially the oldest American alligator in the world living in captivity. He was brought to Belgrade from Germany in 1937, a year after the opening of the Zoo. Muja survived three bombings of Belgrade, the Second World War and all hardships the Zoo went through. (Photo by Marko Djurica/Reuters)

Workers clad in a dog and a wild boar costumes, to represent the outgoing year of the dog and incoming year of the wild boar, clean windows on the side of a hotel in Tokyo on December 13, 2018. (Photo by Kazuhiro Nogi/AFP Photo)

Students in Aone’s elementary school during break in between the class on April 9, 2015. The school has only six students, two of whom are from the same family. Similarly small schools can be found throughout Japan. (Photo by Ko Sasaki/The Washington Post)

Voters line up to cast their ballots at a polling station in the city of Qom, Iran. Elections for Iran's parliament (Majlis) and Assembly of Experts kicked off on Friday, February 26, 2016. (Photo by Ahmad Halabisaz/Xinhua via ZUMA Wire)

Members of the Russian Red Army Choir perform at Water Front Theatre in Beirut September 13, 2014. (Photo by Jamal Saidi/Reuters)

This bat gives a cheeky smile as he gobbles down his food at Singapore Zoo, on September 10, 2013. (Photo by Benny Iskander/HotSpot Media)

“Basunga”. Basunga (3 weeks-old newborn with albinism) is happily sleeping with his cousin. For now, he does not yet realize the difficulties he will face to integrate into the Congolese society as a PWA. The success of his integration will greatly depends of how he accepts himself and his skin condition a and how educated he will be. Photo location: Kinshasa, Congo RDC. (Photo and caption by Patricia Willocq/National Geographic Photo Contest)

Wedges of an orange generate enough current and electrical juice – 3.5 volts – to power an LED. The fruit’s citric acid helps electrons flow from galvanized nails to copper wire in this 14-hour exposure. This image was published in September’s Visions of Earth, a trio of photos that appear in each issue of National Geographic. (Photo by Caleb Charland/National Geographic)