A street in the Cuban capital, Havana, is home to 12 sets of twins, ranging from toddlers to senior citizens. Some say it could be something in the water. Others point to a tree with mystical significance for locals. And maybe it's just chance. Photo: In this September 29, 2013 photo, nine-year-old twin sisters Camila, left, and Carla Rodriguez pose for a portrait along their street in Havana, Cuba. 12 sets of twins live along two consecutive blocks in western Havana, ranging in age from newborns to senior citizens. “We love living on this block because we have twin friends”, said Carla. (Photo by Ramon Espinosa/AP Photo)

Derek Hough, right, and Julianne Hough, co-winners of the award fo rOutstanding Choreography for “Dancing with the Stars”, pose in the press room at the Creative Arts Emmy Awards at the Microsoft Theater on Saturday, September 12, 2015, in Los Angeles. (Photo by Chris Pizzello/Invision/AP Photo)

Some Iraqi candidates for Miss Iraq beauty contest pose in front of the Ishtar Gate at the ancient archaeological site of Babylon, outside the modern city of Hilla, south of the capital Baghdad on December 17, 2015. The beauty contest, which is the first one in more than 40 years, aims to boost tourism in the city and will take place on December 19, 2015. (Photo by Ahmad Al-Rubaye/AFP Photo)

Seljalandsfoss waterfall, located in Iceland. Seljalandsfoss is one of the most famous waterfalls of Iceland. This waterfall of the river Seljalandsá drops 60 metres (200 ft) over the cliffs of the former coastline. It's possible to go behind the waterfall. (Photo by HotSpot Media)

A masked protester talks to a soldier during clashes after the funeral of Brig. Gen. Wissam al-Hassan October 21, 2012. Lebanese soldiers fired guns and tear gas to push back hundreds of protesters who broke through a police cordon and tried to storm the government headquarters in Beirut. (Photo by Hussein Malla/Associated Press)

In this September 11, 2014 photo, villagers climb down the side of a hill used earlier as a dumping ground of asbestos waste on Roro hills in Roro, India. An asbestos mine, abandoned nearly three decades ago still affects the people around it and 18 along with Jema were diagnosed with asbestosis in 2012. Tens of thousands more, some former mine workers, remain untested and at risk. (Photo by Saurabh Das/AP Photo)

“Himalayan Dog”. This dog just appeared out of nowhere and followed us for an entire week during our trekking trip in the Himalayan outback. He always used to sleep in front of our tent and guarded us in the nights. When I decided to get up at 4 a.m. to climb the next 5000 m peak for sunrise he accompanied me as well. On the top he was sitting for the entire 30 minutes on this place looking straight into the countryside. Photo location: Ladakh, India. (Photo and caption by Sebastian Wahlhuetter/National Geographic Photo Contest)

A young woman dressed as a zombie takes part in a zombie parade as part of the Brussels International Fantastic Film Festival 2014 in Brussels, Belgium, 12 April 2014. More than a hundred of participants took to the streets of Brussels. (Photo by Ulien Warnand/EPA)