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)

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)

A stroller walks his dogs in an autumnally colored forest in Cuxhaven, nothern Germany on November 7, 2018. (Photo by Patrik Stollarz/AFP Photo)

Tourists take photos from a panoramic viewing deck on Victoria Peak in Hong Kong, China, 26 January 2019. Hong Kong has been ranked the world's freest economy by the Heritage Foundation, a conservative research and educational institution based in Washington, for the 25th consecutive year, but the researchers also said the judiciary had become less effective. (Photo by Jerome Favre/EPA/EFE)

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)

Students dressed up as Hindu gods Lord Krishna and Lord Shiva participate in a cultural event in their school in Mumbai, India on August 21, 2019. (Photo by Indranil Mukherjee/AFP Photo)

A Saudi woman holds a falcon as she participate for the first time in the 2nd Saudi Falcons and Hunting Exhibition in Riyadh, Saudi Arabia on October 16, 2019. (Photo by Ahmed Yosri/Reuters)