A worker pauses for a sandwich, resting on a girder during the construction of a skycraper. (Photo by Hulton Archive/Getty Images). Circa 1930

A model poses beside a Renault DeZir concept car during the media day of the Shanghai International Automobile Industry Exhibition at Shanghai New International Expo Center on April 20, 2011 in Shanghai, China. The 14th Shanghai International Automobile Industry Exhibition (Auto Shanghai 2011) will be held from April 21 to 28 with the theme of “Innovation For Tomorrow”. About 2,000 carmakers and parts providers from 20 countries are due to showcase 1,100 car models, 75 of which makes their world premieres in the auto show. (Photo by Feng Li/Getty Images)

The crowd watches as stunt pilots Melissa Pemberton, Jurgis Kairys and Skip Stewart of The Immortals fly past pyrotechnics as they perform at The Australian International Airshow on March 1, 2015 in Avalon, Australia. (Photo by Scott E. Barbour/Getty Images)

Models parade at the end of Moschino's Autumn/Winter 2017 women's collection during Milan Fashion Week in Milan, Italy, February 23, 2017. (Photo by Stefano Rellandini/Reuters)

An activist kicks the shields of the military police officers during a demonstration in the military zone of the 27th infantry battalion in Iguala, Guerrero, January 12, 2015. Activists and relatives of the 43 missing trainee teachers from Ayotzinapa's teacher training college broke into the military zone, located less than a mile from where the students went missing, in an attempt to look for the missing students.The remains of only one of the 43 students has been identified so far. (Photo by Jorge Dan Lopez/Reuters)

An Afghan refugee family stands by trucks loaded with their belongings as they wait to go back to Afghanistan with others, at the United Nations High Commissioner for Refugees (UNHCR) office on the outskirts of Peshawar February 13, 2015. Afghan immigrants ordered out of Pakistan in what officials say is a bid to root out militants are, some analysts say, scapegoats being used to distract attention from the authorities' failure to end violence. (Photo by Fayaz Aziz/Reuters)

In this undated photo made available by journal Nature on January 15, 2014, a northern bald ibis (Geronticus eremita) flies in Tuscany, Italy. A new study released Wednesday, January 15, 2014 says the birds choreograph the flapping of their wings, getting a boost from an updraft of air in the wake of the flapping wings by flying behind the first bird and off to the side. When a flock of birds take advantage of these aerodynamics, they form a V. (Photo by Markus Unsöld/AP Photo)

Members of the Guard of Honor of the Presidential Regiment from Russia perform during the “Spasskaya Tower” international military music festival at Moscow's Red Square, Russia, September 10, 2015. The festival runs until 13 Sepember. (Photo by Maxim Shemetov/Reuters)