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)

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)

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)

Aerial view of a farmer feeding ducks at a farm on November 6, 2020 in Sihong County, Jiangsu Province of China. (Photo by Zhang Lianhua/VCG via Getty Images)

A supporter of the opposition parties shouts asking for peace as riot police are block access to the house of the former president Henri Konan Bedie, in Abidjan, Ivory Coast, Tuesday, November 3, 2020. (Photo by Leo Correa/AP Photo)

After a long time renovation project, the old town in Taiyuan city which was founded in 1357, finally lights up and opens to public in Taiyuan City, north China's Shanxi Province, 23 November 2020. (Photo by Rex Features/Shutterstock)

Ellen MacRae a student from Edinburgh University take a lateral flow antigen test at a test centre which is also open to students in Edinburgh Napier University, Queen Margaret University and SRUC on December 1, 2020 in Edinburgh, Scotland. The programme is running in partnership between the University of Edinburgh and other Scottish universities, the Scottish Government and NHS Test and Protect, supporting students leaving their term-time accommodation to travel home at the end of term for the winter break. (Photo by Jeff J. Mitchell/Getty Images)