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)

A Nepalese vetinary and technical team release a rhino after it is relocated in Chitwan National Park some of 250 Kilometer South of Kathmandu on April 4, 2017. Conservationists on April 3 captured a rare one-horned rhinoceros in Nepal as part of an attempt to increase the number of the vulnerable animals, which are prized by wildlife poachers. Five rhinos – one male and four female – will be released into a national park in Nepal's far west over the coming week in the hope of establishing a new breeding group. (Photo by Prakash Mathema/AFP Photo)

Devotees wear costumes made of banana leaves as they head to church to attend mass as part of a religious festival, in honor of St. John the Baptist, also known locally as the “mud people” festival, in Aliaga town, Nueva Ecija province, north of Manila, on June 24, 2017. Farmers coated in mud paraded in Philippine villages on June 24 to mark one of the Catholic nation's most colourful religious festivals. (Photo by Noel Celis/AFP Photo)

Women take part in a march in Santiago on October 19, 2016, to protest against violence against women and in solidarity for the brutal killing of a 16- year- old girl in Mar del Plata, Argentina last week The killing, in which the high school student was allegedly raped and impaled on a spike by drug dealers, is just the latest incident of horrific gender violence in Argentina, which has seen more than a year of mass marches to protest brutality against women. (Photo by Claudio Reyes/AFP Photo)

An environmental activist adjusts his mask while taking part in “The Dead Sea Swim Challenge”, swimming from the Jordanian to Israeli shore, to draw attention to the ecological threats facing the Dead Sea, in Kibbutz Ein Gedi, Israel November 15, 2016. Swimmers from around the world plunged into the salty waters of the Dead Sea on Tuesday to attempt a seven-hour swim across the fabled lake in a bid to draw attention to its environmental degradation. Wearing protective masks and snorkels, 25 swimmers paddled through the muddy water to attempt the 9-mile (15-kilometer) swim from Jordan to Israel. (Photo by Nir Elias/Reuters)

Syrian government troops patrol the newly captured al- Sakhour neighbourhood in the eastern part of the northern city of Aleppo on December 7, 2016 Rebels in Aleppo called for a five- day truce and the evacuation of civilians Wednesday after losing more than three quarters of their territory including the Old City to a Syrian army offensive. (Photo by George Ourfalian/AFP Photo)

In this picture taken on Thursday, December 1, 2016, an Iranian woman covers herself with a blanket due to the cold, while visiting Khour salt lake during her tour of the Mesr desert about 305 miles (500 kilometers) southeast of the capital Tehran, Iran. Deserts make up parts of Iran which have recently become tourist destination for young Iranians looking for a break on their weekend. The increase in tourists to the desert has stimulated economic growth in the area. (Photo by Ebrahim Noroozi/AP Photo)

This August 15, 2016 photo shows two portraits Carolina, one of her holding a weapon while in her uniform for the Revolutionary Armed Forces of Colombia (FARC) 49th front, and in civilian clothing at a guerrilla camp in the southern jungle of Putumayo, Colombia. Carolina, 18, said she has spent three years in the FARC and would like to study engineering after demobilizing as part of a peace deal with Colombia's government. (Photo by Fernando Vergara/AP Photo)