Sumo wrestlers of Nishonoseki clan appeal to the winner of a training bout for the next opponent during a joint training session ahead of the May Grand Sumo Tournament in Tokyo May 2, 2015. (Photo by Toru Hanai/Reuters)

Bulgarian Roma women from the close-knit Kalaidjii clan attend a so-called “bride fair” in a suburb of the city of Plovdiv April 13, 2015. Each year Roma families from the close-knit Kalaidjii clan gather during what they call a “bride fair”, an event offering parents a chance to meet and to arrange marriages for their children. (Photo by Stoyan Nenov/Reuters)

Crowds look on as Xolo the Giant Dog, one of the giant Royal De Luxe street puppets taking part in Liverpool's World War I centenary commemorations, walks through the streets of Liverpool on July 25, 2014 in Liverpool, England. French street theatre company Royal de Luxe are putting on a show throughout the city as part of Liverpool's World War I centenary commemorations from July 23-27. The giant puppet grandmother has slept in the hall for two days as part of “Memories of August 1914”. As the giants tour the city the Little Girl Giant and her dog Xolo will meet up with the giant Grandmother telling the story of life leading up to World War One. (Photo by Christopher Furlong/Getty Images)

For centuries the Highlands peoples of Papua New Guinea fought over land, women and pigs. Sorcery and battle skills could elevate a clan to Bigmanship, where the bigger the “presentation”, the bigger the man. Clans therefore would paint their bodies and create fearsome masks as part of their psy. Here: These are the terrifying tribe of “mudmen” from a remote part of Papua New Guinea. (Photo by Jeremy Hunter/Exclusivepix Media)

These powerful images capture the spear-wielding tribes of Papua new Guinea who believe they are possessed with the spirit of the crocodile. They show how the Kangunaman clansmen scar their backs to resemble reptile scales while the Huli Wigmen wear elaborate headdresses to signal they are ready for battle. (Photo by Trevor Cole/Media Drum World)

Behaviour: Mammals category. Giant Gathering by Tony Wu, USA. Dozens of sperm whales mingled noisily off Sri Lanka’s northeast coast, stacked as far down as Tony could see. This was a congregation of dozens of social units, like a gathering of the clans. Aggregations like this could be a critical part of the whales’ rich social lives but are rarely reported. Some two thirds of the population was wiped out before commercial whaling was banned in 1986. This kind of major gathering could be “a sign that populations are recovering”, says Tony. (Photo by Tony Wu/Wildlife Photographer of the Year 2017)

The Kazakhs are the descendants of Turkic, Mongolic and Indo-Iranian tribes and Huns that populated the territory between Siberia and the Black Sea. They are a semi-nomadic people and have roamed the mountains and valleys of western Mongolia with their herds since the 19th century. The ancient art of eagle hunting is one of many traditions and skills that the Kazakhs have, in recent decades, been able to hold on to. They rely on their clan and herds, believing in pre-Islamic cults of the sky, the ancestors, fire and the supernatural forces of good and evil spirits.

A new book published by the UK Natural History Museum showcases some of the most memorable underwater photographs taken over the last few decades in its annual wildlife photographer of the year competition. Here: Giant gathering by Tony Wu. “The first indication that something extraordinary was going on were the blows, huge numbers of them – the exhalations of huge numbers of whales. Entering the water, the photographer witnessed an extraordinary scene”. (Photo by Tony Wu/Unforgettable Underwater Photography/NHM)