Immortality has been a hot topic for humans since the dawn of civilisation. One of the world's first literary works was the Epic of Gilgamesh, written by the ancient Mesopotamians more than 4,000 years ago. It was an epic about a mythological hero-king and his search for immortality. This ancient story is believed to be based on even older legends from the Sumerian empire. The subject of immortality has been debated theologically throughout time in almost all cultures and is still the focus of religions. It will continue to be a subject for heated debate, probably until we have somehow conquered it. We animals have an inherent flaw that applies a limit to the length of our lives. Mortality seems to have an evolutionary advantage over immortality; it greatly enhances our ability to adapt to an ever-changing environment. Our descendants, due to the forces of natural selection, can be superior to us. Selective forces have already prolonged our natural lives and, with advances in modern medicine and engineering, we can imagine a future in which cemeteries are obsolete - assuming we don't destroy ourselves in the meantime. A few creatures have actually achieved biological immortality. The one that stands out is a jellyfish called Turritopsis nutricula. This humble creature, just visible to the naked eye, has cheated the Grim Reaper and is slowly spreading across the planet's oceans. This jellyfish has found a way to reverse the process of ageing as an emergency measure to escape death, and then to grow old again and repeat the process. When faced with imminent demise due to trauma, starvation or other hardship, it has the ability to revert to a juvenile polyp state. This ability is probably unique in all of the animal kingdom and allows the jellyfish to avert death, making it biologically immortal. Experiments have shown that 100 per cent of the specimens will revert back to a juvenile state when challenged, making all specimens of Turritopsis nutricula immortal. The only way to destroy this jellyfish is to remove its nerve centre from its body. A different strategy for biological immortality is displayed by a creature called a hydra, a fresh water animal a few millimetres in length. The hydra has fascinated scientists because of its unique ability to halt senescence (ageing), making it also biologically immortal. If injured or severed, the hydra is able to regenerate tissue. If you squeeze a hydra through a gauze to separate it into individual cells, the cells will search for each other and coalesce into the whole creature again. The oldest living single organism is actually a tree named bristlecone pine found in the Rocky Mountains in New Mexico, Arizona. These trees live in very harsh, cold and dry environments and grow very slowly. As the tree ages, there is only a very thin sliver of cells that connects the roots to the few remaining leaves. These trees are more than 5,000 years old. There are other trees, such as the aspen, which are clones of the original that have been dated to about 10,000 years old. It may be possible through science for us eventually to obtain immortality like the hydra and Turritopsis nutricula, by regenerating or even reverting to a juvenile stage. Through science it may also be possible one day to obtain immortality of consciousness without a biological component. We may be able to upload our sentient mind by converting it to signals in a complex silicon wafer, which would mean our consciousness could last forever. These science-fiction ideas have been posed by many futurists such as Ray Kurzweil. From a scientific point of view, we are far from discovering the secrets of immortality, but scientists have found some tantalising ways to increase our longevity. There is a naturally formed enzyme call telomerase. It is part of the protective protein caps at the ends of our chromosomes and helps protect the chromosomes from degradation during cell division. It enables the cells to divide continually without DNA deterioration. In an experiment at the Spanish National Cancer Centre in Madrid, scientists genetically modified mice to produce 10 times the normal level of telomerase and found that these mice lived 50 per cent longer than regular mice. As usual there is a spanner in the works. This process of cell division is the same as what occurs when a cell becomes cancerous, so a lot more work needs to be done before this technique can be applied safely to humans. There are also the ethical considerations of science-induced immortality, which are sure to ruffle some feathers. From a Buddhist point of view, obtaining immortality this way would mean a life of eternal suffering. On the brighter side, it would also provide a lot more time to obtain enlightenment.