Saddleback tortoises have longer necks and legs than their domed buddies, and have a shell shape that lets them extend their heads up higher. These tortoises live on drier islands with scattered plant life that's often hard to reach from the ground. Over many generations the tortoises with "saddleback"-shaped shells were more successful at getting food from higher bushes and trees than dome-shaped tortoises. The tortoises that ate better were also better able to survive and reproduce. (Photo credit: Tui de Roy/Minden Pictures)