The story of Robinson Crusoe teaches us that while a person alone on an island has obligations toward nature and toward himself, he does not have rights, since there is no one there with obligations to him. In other words, obligations are more basic than rights and always precede them. Moreover, obligations are absolute, while rights are relative. Thus every individual has obligations. And this is true regardless of ability, for obligations are always determined by – and proportionate to – one’s ability to fulfill them.
For a long time, it was held that human beings only had obligations to one another. The growing consciousness of the fragility of the earth and the vulnerability of living species has expanded our understanding of obligation to include nature as a whole. For the same reasons, many writers argue that animals also have rights.