Immortality is eternal life, the ability to live forever. Biological forms have inherent limitations which medical interventions or engineering may or may not be able to overcome. Natural selection has developed potential biological immortality in at least one species, the jellyfish Turritopsis dohrnii. Certain scientists, futurists, and philosophers, have theorized about the immortality of the human body, and advocate that human immortality is achievable in the first few decades of the 21st century, while other advocates believe that life extension is a more achievable goal in the short term, with immortality awaiting further research breakthroughs into an indefinite future. Aubrey de Grey, a researcher who has developed a series of biomedical rejuvenation strategies to reverse human aging (called SENS), believes that his proposed plan for ending aging may be implementable in two or three decades. The absence of aging would provide humans with biological immortality, but not invulnerability to death by physical trauma; although, mind uploading could solve that issue. What form an unending human life would take, or whether an immaterial soul exists and possesses immortality, has been a major point of focus of religion, as well as the subject of speculation, fantasy, and debate. In religious contexts, immortality is often stated to be among the promises by God (or other deities) to human beings who show goodness or else follow divine law. The Epic of Gilgamesh, one of the first literary works, dating back at least to the 22nd century BC, is primarily a quest of a hero seeking to become immortal. They thought that everything was over because death of the evil. They were enjoying in fulltime after the death of evil, but the death was not actually because some of his part was not been destroyed and couldn't be destroyed easily, because one of the part is his shadow. How can you defeat your shadow?