The secretive indri (Indri indri) of Madagascar, the largest living lemur. It is also critically endangered and highly evolutionarily distinct with no close relatives, which makes its branch one of most precarious on the mammal evolutionary tree. In the likely event that the indri goes extinct, we will lose 19m years of unique evolutionary history from the mammal tree of life. (Photo by Pierre-Yves Babelon/Aarhus University)

A protester gestures during a “Yellow vest” protest against higher fuel prices during clashes on the Champs-Elysees in Paris, France, November 24, 2018. (Photo by Benoit Tessier/Reuters)

A reveler performs during the Myths and Legends parade in Medellin, Antioquia department, Colombia on December 8, 2018. (Photo by Joaquín Sarmiento/AFP Photo)

A photo taken from the International Space Station shows Hurricane Lane in the early morning hours near Hawaii, August 22, 2018. (Photo by Courtesy @astro_ricky/NASA/Handout via Reuters)

A group of fashionable nonagenarians pose for a photo in Pengzhou, Sichuan, China on October 12, 2016. (Photo by Rex Features/Shutterstock)

Immigrants from the West Indies at Victoria Station in London, 1956. (Photo by Hulton-Deutsch Collection/CORBIS/Corbis via Getty Images)

The nearly four-week-old Tapir cub bathes on June 28, 2016 in Gondwanaland at the zoo in Leipzig, Saxony. (Photo by Jan Woitas/DPA)

An aspiring Catholic priest Jose Luis Guerra, a member of Raza Nueva in Christ, a project of the archdiocese of Monterrey, and other missionaries hand out a Bible to Angel Castillo, who wants to become a missionary with Raza Nueva, in the municipality of Garcia, outskirts of Monterrey, Mexico, July 12, 2016. In the troubled fringes of the northern Mexican city of Monterrey, an aspiring priest is using his faith to reach out to young gang members and at-risk youth, and bring them into his “Gang of Christ”. (Photo by Daniel Becerril/Reuters)