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 general view shows the part of the skyline of Dubai covered in an early morning fog on October 5, 2015. (Photo by Rene Slama/AFP Photo)

A mahout bathes his elephant in the river Sabarmati on a hot summer day in Ahmedabad, India May 21, 2017. (Photo by Amit Dave/Reuters)

In this July 11, 2016 photo, a young, masked drug trafficker poses for photos holding his guns at a slum in Rio de Janeiro, Brazil. Teenagers openly tote guns while they work as guards, lookouts and distributors for drug lords operating just a few miles from where hundreds of thousands and tourists and athletes will be for the Aug. 5-21 Olympic Games. (Photo by Felipe Dana/AP Photo)

Iberian lynx Mistral jumps in a field after being released by Portugal's Minister of Environment Joao Matos Fernandes (unseen) and others in the Mount Milhouro (Herdade da Cela) region in Mertola, Portugal, 13 May 2016. Mistralis the 18th lynx bred in captivity released since late 2014. (Photo by Nuno Veiga/EPA)

A cat dressed in a traditional Ukrainian embroidered shirt takes part in a parade in Kiev, Ukraine on May 28, 2016. (Photo by Gleb Garanich/Reuters)

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

Twin brothers Keith (L) and Deano Stapleton (R) interact with one another as people gather to witness the winter solstice on December 21, 2022 in Newgrange, Ireland. Crowds are gathering at Newgrange in Co Meath, this morning for the winter solstice – the astronomical phenomenon that marks the shortest day and the longest night of the year. Newgrange is a Stone Age (Neolithic) monument in the Boyne Valley, County Meath, it is the jewel in the crown of Ireland's Ancient East and was constructed approximately 5,200 years ago (3,200 B.C.) which makes it older than Stonehenge and the Great Pyramids of Giza. (Photo by Charles McQuillan/Getty Images)