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 pedestrian carries an umbrella as they stroll past an advertisment as a rainstorm moves through Sacramento, Calif., Wednesday, February 13, 2019. Rain is falling widely in Northern California and is expected to spread south. (Photo by Rich Pedroncelli/AP Photo)

Syrian refugee boys play with toy guns at Eminonu district in Istanbul, Turkey, 08 January 2019. (Photo by Sedat Suna/EPA/EFE)

Sun Rongchun, 57, exercises with an improvised cervical traction device attached to a high bar at a sports complex in Shenyang, Liaoning province, China on April 9, 2019. (Photo by Sheng Li/Reuters)

A model presents a creation by Indian designer Amit Aggarwal during the grand finale of the Lakme Fashion Week (LFW) Summer/Resort 2020 in​ Mumbai, India, 16 February 2020. (Photo by Divyakant Solanki/EPA/EFE)

A mural painting by graffiti artist Eme Freethinker features likenesses of US President Donald Trump (R) and Chinese premier Xi Jinping wearing face covers in Berlin on April 28, 2020 amid the new coronavirus COVID-19 pandemic. (Photo by John Macdougall/AFP Photo)

Journalists wear face mask and keep distance as they attend news conference by German Health Minister Jens Spahn about the developing of the coronavirus crisis test strategy in Berlin, Germany, Thursday, August 6, 2020. (Photo by Markus Schreiber/AP Photo)

People celebrate media announcing that Democratic U.S. presidential nominee Joe Biden has won the 2020 U.S. presidential election in Alphabet City neighborhood of Manhattan, in New York City, U.S. November 7, 2020. (Photo by Andrew Kelly/Reuters)