Imagine reaching old age, then pressing a biological reset button and starting life all over again. Sounds like science fiction, right? But there’s a real creature in the ocean that does just that—the immortal jellyfish (Turritopsis dohrnii).
When we think about living forever, it’s usually in the realm of myths or fiction. But in the natural world, some animals like the immortal jellyfish come remarkably close.
Here’s a look at some of the most fascinating species that challenge what we think we know about ageing.
1. The immortal jellyfish (Turritopsis dohrnii)
Let’s start with the only known animal that can essentially live forever.
The immortal jellyfish, discovered in the Mediterranean, has the incredible ability to revert to its earlier life stage—a process called transdifferentiation. When it’s injured, stressed, or simply ageing, it turns back into a polyp (its juvenile form), starting life all over again.
This reset process can repeat endlessly, theoretically making the jellyfish biologically immortal. It’s still vulnerable to predators and disease, but if nothing kills it, it can dodge death by simply rebooting.
2. Hydra
Hydras are tiny freshwater creatures closely related to jellyfish. What sets them apart is their continuous regeneration. Thanks to a large number of stem cells that never stop renewing, hydras don’t appear to age at all.
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In lab settings, some have lived for decades with no signs of deterioration. Scientists believe hydras could be biologically immortal under ideal conditions, although they rarely live forever in the wild.
3. Bdelloid rotifers
These microscopic animals are tougher than they look. Bdelloid rotifers can survive extreme environments—radiation, lack of oxygen, and even tens of thousands of years frozen in Siberian permafrost.
A study published in Current Biology in 2021 showed they could return to life after 24,000 years frozen, which makes their resilience nothing short of jaw-dropping. They don’t live forever, but they pause ageing for millennia when frozen.
Lobsters never really stop growing (Source: Freepik)
4. Planarian flatworms
If you cut a planarian flatworm in half, you won’t kill it—you’ll get two new worms. Their regenerative powers are so strong that even a single cell can regrow an entire organism in some species.
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Even more fascinating? Some planarians appear to maintain their telomeres, the protective caps on chromosomes that typically shorten with age in most organisms. This suggests they may have found a workaround to biological aging.
5. Lobsters
Lobsters never really stop growing. Unlike humans, they keep getting bigger with age and remain fertile for life. This is partly thanks to high levels of telomerase, an enzyme that helps repair DNA.
While not immortal—they eventually die, often from complications during molting—lobsters don’t age in the conventional sense. In the right conditions, they could theoretically live well over 100 years.
6. Greenland shark
This deep-sea shark lives in the icy waters of the North Atlantic and may be the longest-living vertebrate on Earth. Scientists have estimated that Greenland sharks can live up to 400–500 years, with some still swimming today born in the 1600s.
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These sharks grow slowly—about 1 cm per year—and don’t reach sexual maturity until they’re around 150 years old. Aging is slow and graceful for these deep-sea giants.
These animals don’t just stretch the limits of lifespan—they stretch our understanding of biology, ageing, and regeneration. Scientists are studying them to learn how cells regenerate, why some organisms avoid age-related diseases, and whether humans can one day benefit from their secrets.
While human immortality remains a fantasy, these creatures show that in nature, the rules of life and death aren’t always set in stone.
