TV's most extreme survival challenge just grew extra-large. Veteran survivalists familiar with the stripped-down drill after appearing on "Naked and Afraid" attempt to survive in a desolate, dangerous environment for 40 days -- 19 more than they previously experienced on the show. Pushing the very limits of human endurance, the men and women must all vie for the same limited food, water and shelter while avoiding territorial-sensitive predators and venom-filled reptiles. Because there is no other choice, the competitors quickly get to know one another -- and their surroundings -- and hope that their instincts, survival skills and intestinal fortitude serve them well.