Since the dawn of history, the idea of immortality has intrigued humans—sometimes to the point of obsession. Myths from every corner of the globe and every period in history tell of gods and goddesses who live forever and human heroes who strive to possess that knowledge and ability. Today, many of the current major religions of the world offer the reward of eternal life for pious believers, which is a testament to man’s will to overcome death.

With the advent of modern science, some scientists began examining the biology behind aging. In the process, they have developed theories that claim to slow the effects of aging. There is no doubt that modern medicine has vastly prolonged human lives over the last one hundred years, and as medical technology progresses even more, the average human life span will no doubt also increase. Some scientists believe that if medical science continues to progress as its current rate, over the next few decades, people will begin to regularly live to one hundred and we will even see the first person live to one hundred fifty.

But that isn’t good enough for some people who want to live eternally, or at least indefinitely.

No one at this point believes that humans can become indestructible, but some believe—based on examples from nature—that senescence (biological aging) can be massively retarded or even stopped. This may sound strange, but a closer look reveals that there is some truth to the theory.

The small freshwater class of organisms known as hydras are believed to be biologically immortal. Hydras have no brain, muscles, or vertebrae, and are therefore susceptible to death in a number of ways. But they have incredible regenerative abilities. The hydra’s regenerative abilities, which allow it to recover quickly from injuries, are believed to be connected to their lack of aging.

The Turritopsis dohrnii (or immortal jellyfish) is also believed to be another animal that doesn’t age. In fact, the immortal jellyfish has the unique ability to retard its life span by returning to the polyp stage when it is faced with adverse conditions such as starvation or extreme changes in temperature.

Other animals that have displayed a “negligible senescence” include different species of tortoises, sharks, and rockfish, all of which are believed to have the ability to live two hundred years or more.

What are the long-term implications for humanity? Scientists have been examining hydras and immortal jellyfish in order to determine if something can be taken from those animals to help slow the aging process in humans. At this point, taking action to extend life is still theoretical, but experiments may begin in the future where humans are injected with hydra cells.

The time for experimentation is probably closer than you think.