Naturalist: For decades we have known that the tuatara, a New Zealand reptile, have been approaching extinction on the South Island. But since South Island tuatara were thought to be of the same species as North Island tuatara there was no need to protect them. But new research indicates that the South Island tuatara are a distinct species, found only in that location. Because it is now known that if the South Island tuatara are lost an entire species will thereby be lost, human beings are now obliged to prevent their extinction, even if it means killing many of their unendangered natural predators. Which one of the following principles most helps to justify the naturalists' argumentation? ['In order to maximize the number of living things on Earth, steps should be taken to preserve all local populations of animals.', 'Human activities that either intentionally or unintentionally threaten the survival of an animal species ought to be curtailed.', 'The threat of local extinction imposes no obligation to try to prevent that extinction, whereas the threat of global extinction does impose such an obligation.', 'When an animal is in danger of dying, there is an obligation to help save its life, if doing so would not interfere with the health or well-being of other animals or people.']