Since we have acknowledged the existence of  life and made attempts to understand and define it, we have accepted death as its eternal companion. We have come to observe that anything that is alive, must die someday. Nature itself demonstrates remarkable variation in lifespan across organisms- mayflies survive for 24 hours, a housefly’s life lasts between 1 week to 2 weeks, while a macaw can live up to 100 years. Across cultures, philosophies, and scientific disciplines, the cycle of life and death has been regarded as one of the few universal constants of living organisms.

However, not all organisms have a limit set to their lifespan. Some living organisms have been found to possess the boon to live on forever. Under ideal conditions free from predation, disease, or extreme environmental trauma, these organisms can live indefinitely through unique survival strategies.

In microbes, immortality is achieved by escaping individual death through symmetric division or metabolic suspension. Many complex multicellular organisms are also able overcome natural death by reversing their life cycles or constantly renewing their cellular structures. Turritopsis dohrnii is a marine creature that reverses its life cycle whenever subjected to conditions of duress like physical stress, starvation, and damage. Hydra is another genus of freshwater polyps (an aquatic invertebrate in the phylum Cnidaria) mostly made of active stem cells these stem cells constantly divide and completely replace every cell in the Hydra's body roughly every 20 days, preventing it from ever growing old.