This is the sort of creature the ancient Egyptians would have worshipped, if only they'd known about it.
– An h2g2 Researcher
Imagine if, after the first time you had sex, you reverted back to a pre-pubescent stage. You'd be virtually immortal, so long as you managed to score once you became sexually mature again (there are some other factors that follow, but this is the main requirement). Sound like a dream? Well there is such a creature which does this; it's called Turritopsis nutricula although, quite rightly, its common name is 'the immortal jellyfish'.
The hydrozoans, which grow to a maximum adult size of 5mm1, originated in the Caribbean region, but are now located in warm waters all around the globe. Marine biologist Maria Pia Miglietta of Pennsylvania State University has identified specimens as widely spread as Panama, , Italy and Japan. She says the age reversal is 'equivalent to a butterfly that goes back to being a caterpillar'.
This species of freshwater jellyfish can tolerate salt water, according to John Darling of the US Environmental Protection Agency's National Exposure Research Laboratory in Cincinnati, so no sea or ocean is safe from their colonisation. However, there have been no reports that the jellyfish are having an adverse effect on the local sealife of newly-invaded territories. One of the reasons that the jellyfish aren't the dominant species on the planet by number is because they are a favourite food of green turtles.
The age reversal is not automatic; after sexual maturity is achieved, a second factor needs to kick in – a kind of stress. This stress could be, for example, being sucked into a ship's keel as ballast, transported around the world then ejected into a strange new world, or a morbid fear of turtles.
This age reversal is surely the Holy Grail of modern science, second only to beating death itself, or curing cancer. Scientists are hard at work testing the genetic make-up of some specimens of Turritopsis nutricula to see if the 'longevity gene' can be identified and isolated. This leads to the conclusion that the jellyfish are only immortal if they manage to evade the clutches of hungry turtles and human scientists desperate to discover their font-of-eternal-youth secret.
Imagine the marketable value if the longevity gene could be bottled and sold as a tonic? But if we all returned to our pre-pubescent state, sales of acne-treatments and spot-concealers would also sky-rocket, and the global economy would be back on track with the surge in iPod sales alone.
Other Kinds of Immortality
Amoebas are immortal, as are bacteria, which reproduce by splitting. Each offspring is a continuation of the individual that existed before the split, and they only die if they run out of food. Certain species of fish do not appear to age; they continue to live and grow until they are so large they can't catch enough food to maintain their bodies.