The secrets of old, old age

It’s the 28^th century BC. Stonehenge is being built, Ancient Egypt is still new, and in California, a bristlecone pine tree has just started to grow. Fast-forward almost five thousand years, and that tree, nicknamed ‘Methuselah’, is still alive today. It might be the world’s most ancient living organism – but whether it is or not is actually a very complicated question.

How do we even measure age?

The easiest way to determine something’s age is simply to know when it was born. However, birthdates are generally only recorded for humans and our pets – what about everything else?

Often scientists will tag or mark animals to study them. Even if they don’t know when it was born, this allows them to keep track of a minimum age for that individual. Other methods include:

• Counting growth rings. This is most common for trees, but also works for shells, corals and bones.
• Measuring size if an organism grows at a constant rate.
• Carbon-dating and other types of radiometric dating.

Clonal Organisms

Have you ever taken a cutting from a plant to grow your own? Starting with a single branch, you can grow a full plant that’s a perfect clone of the original. Some organisms reproduce this way naturally, and the “clonal colonies” they form can last for thousands of years.

While you might think that clones shouldn’t count as the same organism, many clonal colonies are connected, often sharing the same root systems. What look like individual plants are actually just the body parts of a single supermassive, super-old living being.

Back from Dormancy

Another way for something to extend its lifespan is to go dormant. A dormant organism isn’t actually dead, but it stops acting alive, like it’s been put on pause.

Seeds are a good example of dormancy – they can remain as seeds for years, then grow into a plant when the time is right. In 2020, scientists grew several date palm trees from seeds that had been dormant for two thousand years.

Adult organisms can also go dormant. Thirty thousand year-old frozen worms have been successfully revived by scientists, as have bacteria from 250 million years ago.

Biological Immortality

There are many ways organisms extend their lifespans, but is it possible to live forever? For most species the answer is no, but some animals are what is called ‘biologically immortal’.

The immortal jellyfish (Turritopsis dohrnii) has a life-cycle with several distinct stages. However, the adult jellyfish has the ability to turn back into its younger form – like if a frog could become a tadpole again. This reverses the aging process, meaning that immortal jellyfish cannot die of old age (although they can still be killed).

This article was published in Issue 54 of Double Helix magazine (https://www.csiro.au/en/Education/Double-Helix). Copyright for this article is held by CSIRO.