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 sandstorm hits the city of Zhangye in Gansu province, China on November 27, 2018. (Photo by Reuters/China Stringer Network)

John McEnroe kicks back a television camera that he felt was crowding him on the court during the finals of the U.S. Pro Indoor Tennis Championships in Philadelphia January 27, 1985. McEnroe defeated Czech Miroslav Mecir to win the tournament. (Photo by Amy Sancetta/AP Photo)

Two friends attempt to balance in the icy conditions in Newcastle, England on February 2, 2019. Boozy Brits across the UK took to the streets last night to ensure they got February off to a wet start after “Dry January”. (Photo by Craig Connor/North News and Pictures)

Soldiers on exercise in Kenya. The image, by Sergeant Dek Traylor, is among the section winners in the UK Army Photographic Competition 2018. (Photo by Sergeant Dek Traylor/PA Wire Press Association)

Members of the San Francisco Gay Freedom Day Marching Band and Twirling Corps do their thing down San Francisco's Market Street, June 27, 1982. Police estimate the crowd to be 300,000 for the Lesbian/Gay Freedom Day parade and rally. (Photo by Carl Viti/AP Photo)

Leonhard Nienbling is shown with his 6-month old pet baboon Jackl, who holds a 6-month old kitten, its playmate, June 29, 1952. Niebling has quite an animal collection at his home in Zirndorf, Germany. (Photo by Heinrich Sanden/AP Photo)

A cat tries to find dry ground around an apartment complex in Houston after Hurricane Harvey hit on Aug. 30. Harvey made landfall in South Texas on August 25, leading to days of downpours that dumped more than 50 inches of rain. Harvey damaged or destroyed about 200,000 homes as the storm system flooded much of Houston and smaller coastal communities. (Photo by Scott Olson/Getty Images)