Brain-on-a-chip. Dazzling in green and magenta this image shows the nerve fibres (in green) produced by neural stem cells (in magenta) as they grow on a synthetic gel. Captured by a technique known as confocal microscopy, the image is part of research shedding light on how tinkering with the environment can affect the way in which nerve fibres grow. (Photo by Collin Edington and Iris Lee/Massachusetts Institute of Technology/Wellcome Images)

Julian, left, is photographed by his mother with friend Gianluca, right, under water at a public pool in Gelsenkirchen, Germany, on a hot Friday, July 3, 2015. Germany faces a heat wave with temperatures up to 38 degrees Celsius (100 degrees Fahrenheit) at the weekend. (Photo by Martin Meissner/AP Photo)

Police detain demonstrators during an action against Russia's attack on Ukraine in St. Petersburg, Russia, Monday, February 28, 2022. Protests against the Russian invasion of Ukraine resumed on Monday, with people taking to the streets of Moscow and St. Petersburg and other Russian towns despite mass arrests. (Photo by Dmitri Lovetsky/AP Photo)

A greater bird of paradise (Paradisaea apoda) displaying in Badigaki Forest, Wokam Island (Aru Islands, Indonesia). Found here in Aru and on adjacent New Guinea, the greater bird of paradise represents about 40 different species of birds of paradise that depend on intact rainforest across the New Guinea region spanning eastern Indonesia and Papua New Guinea. With more than 80% of forest cover still intact, this region represents the largest remaining block of rainforest in the entire Asia-Pacific. (Photo by Tim Laman/naturepl.com/LDY Agency)

UFC women's bantamweight champion Holly Holm and Miesha Tate face off during the UFC 196 weigh ins at the MGM Grand Garden Arena in Las Vegas on Friday, March 4, 2016. (Photo by L.E. Baskow/Las Vegas Sun via AP Photo)

The popular K-pop group Blackpink watch the fireworks at Etihad Park from the stage at the end of the show in Abu Dhabi on Saturday, February 4, 2023. (Photo by Live Nation Entertainment)

Female members of the Chinese People's Liberation Army (PLA) honour guard stand behind a string to ensure that they are in a straight line before a welcoming ceremony for Russian President Vladimir Putin outside the Great Hall of the People in Beijing, China, June 25, 2016. (Photo by Kim Kyung-Hoon/Reuters)

An undated handout picture made available on 29 April 2016 by the Toronga Zoo shows a baby echidna making a remarkable recovery after being attacked by chickens in a family's backyard at the Taronga Zoo in Sydney, Australia. (Photo by EPA/Taronga Zoo)