Soldier boys at Fort Dix, N.J., learn something about guns during their working hours, as they show their girlfriends at a camp dance, December 13, 1940. In front row, playing with the coin amusement gun, from left: Pvt. Tom D'Amato of West Orange; Rose Sinkewicz, behind gun site, of Trenton; Julia Ivans of Trenton, and Pvt. Vernon Landers of Kearney. Back row: Pvts. William Sargent and William Corlies of Philadelphia. (Photo by AP Photo)

British theoretical physicist Stephen Hawking, Cambridge University Professor and Fellow, circa 1985. Stephen Hawking, the brightest star in the firmament of science, whose insights shaped modern cosmology and inspired global audiences in the millions, has died aged 76. (Photo by Gemma Levine/Getty Images)

A guest proposes to his companion as they arrive for the screening of “Mektoub, My Love: Intermezzo” during the 72nd annual Cannes Film Festival, in Cannes, France, 23 May 2019. The movie is presented in the Official Competition of the festival which runs from 14 to 25 May. (Photo by Julien Warnand/EPA/EFE)

Guards wait for the start of former Egyptian President Hosni Mubarak's funeral at Field Marshal Mohammed Hussein Tantawi Mosque east of Cairo, Egypt on February 26, 2020. (Photo by Amr Abdallah Dalsh/Reuters)

A fruit bat eats lettuce as it hangs from a rope during a behind the scenes interactive live stream from the Oakland Zoo on April 16, 2020 in Oakland, California. Since the Oakland Zoo has been closed to the public during the shelter in place, they are offering a subscription based service that will feature five weekly behind the scenes live streamed interactive programs that will feature animal keepers and their animals. Viewers are able to interact with the keepers by submitting questions to about the animals. (Photo by Justin Sullivan/Getty Images)

Children in a Hong Kong refugee resettlement area watch as former Vice President Richard Nixon shows them his badminton service. Nixon visited Hong Kong, April 4, 1964, during his tour of countries in the Far East. (Photo by AP Photo)

Animal rights activists protest against the use of animal leather in fashion businness, a few days before the fashion week opening in Milan, Italy, 16 September 2018. (Photo by Matteo Bazzi/EPA/EFE)

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)