Ask Glenn

What’s the oldest-living animal, and how old does it get?

This month's Question of the month, asked by Raza

We can’t be sure which animal lives longest, as the world’s oldest animal may still be alive and undiscovered somewhere in the wild. But the oldest we’ve found yet is a kind of mussel that can live for over 405 years!

A mussel ?! Like a little, squidgy, clam-type-thing? I thought for sure it’d be a tortoise or a whale or something.

Well, they do live pretty long, too. Giant Galapagos tortoises can live up to 177 years, and Bowhead whales up to 211. In fact, many large animals live very long lives. According to zoo records, if they’re healthy (and maybe a bit lucky), Elephants and parrots can live up to 70 years, and swans for over 100 years!

Elderly mollusc

So why do they live so long, then?

No-one knows for sure, but there are a few general patterns that give us clues. Size, for example, seems to be important. In general, the larger an animal is, the longer it lives. This helps to explain why giant whales and tortoises can live for over a century, while tiny mammals like shrews get less than three years, and tiny insects like mayflies less than a day.

But that clam-thing isn’t very big, is it?

Good point. It isn’t. In reality, there are plenty of exceptions to the “bigger animals live longer rule”, so it’s clearly not as simple as that. Another clue seems to suggest that it’s not just how big, but how active an animal is that decides its lifespan. As larger animals are less active than smaller ones (think of a lumbering tortoise or whale versus a scurrying shrew), it may be that they live longer because they exert less effort just getting through life. Many small animals spend most of their time and energy scurrying around after food and away from predators – they’re always “on the go”. Large animals have fewer predators and, often, less mobile prey. Bowhead whales simply drift into underwater clouds of plankton for a meal, while giant tortoises pursue the not-very-fast-moving grasses and fruits of the Galapagos Islands. Similarly, the Icelandic Cyprine – our 405-year old mussel – just sits on a rock and filters its food out of the ocean. Not much effort needed there.

Getting old probably doesn’t bother it much, either. It doesn’t have eyes or feet, so it doesn’t need glasses or a walking stick when they wear out. And getting grey and wrinkly isn’t a problem, since it basically started out that way, anyway.

And that’s the oldest animal there is?

Well, technically there is one older. You might not think of sponges as animals, but they’re classified as simple animals or primitive metazoa. If you count them, then there’s one kind – the glass sponge – which can live for an incredible 15,000 years! If you go beyond animals to other kinds of organism, some live even longer than that.

How much longer?

Some individual trees and plants can live for thousands of years – like Bristlecone pines, which can live for maybe 5,000 years or more. But if you think about it, some plants reproduce by budding bits of themselves off into new plants – in effect, cloning themselves. These cloned plants and trees cluster together, and while some parts of the cluster die off, the rest live on, and you could say the whole colony is one, big, living organism – like bits of the same plant body, rather than different individuals. If you count these, then the oldest plant found yet is a Tasmanian King’s Holly cluster found by Australian botanists in 1996. Using chemical dating methods, they found it was over 46,000 years old!

No way! Then that has to be the oldest living thing – right?

Well, again, that depends how you define “living”. Some fungi and bacteria can turn into dormant (or practically lifeless) spores when their water or nutrient supply dries up, and spring back to life millions of years later when watered and fed. Microbiologists have found spores of a bacillus (or “rod-shaped”) bacterium over 250 million years old, and successfully brought it back to life in the lab. Also, like plants, many fungi and bacteria simply bud off from each other to reproduce, growing in identical colonies or clones. Some of these, like some archaean (or “ancient”) bacteria have been around for over 3 ½ billion years – since the beginning of life on Earth – and they’re still going strong. In effect, they never age. They’re immortal.

So if some things can live forever, why do the other things get old at all?

Once again, no-one can say for sure yet, but some scientists think it comes back to the idea of activity we were talking about earlier. Different organisms have different rates of metabolism – which is basically how fast they break down food and turn it into energy. Simple and small organisms tend to have faster metabolic rates, have to “feed” constantly, and often live at a high pace to sustain themselves. Larger, more complex organisms can often get away with eating a few times a day, have slower metabolic rates, and are less active. It’s thought that during daily life, the process of breaking down food and turning it into energy might actually lead to aging by damaging the DNA inside cells. So the more active the organism, the faster it “burns out” and ages itself.

So the secret to living forever is to do as little as you can? Ha! I knew it! In that case, I’m just going lounge around in front of the TV as much as possible from now on, and there’s nothing my parents can do about it! Bwa ha ha haa!!

Unfortunately, that’s not going to work, I’m afraid. In fact, that will probably do just the opposite. Our bodies and brains need exercise and stimulation to keep us looking, thinking and feeling young. Slobbing only leads to health problems as your body and brain weaken through too little use. From all scientists know so far, staying fit seems to be the best way to stay younger for longer.

I guess it seems to work for that little clam-type-thing, anyway.

Why do you say that?

Well, he obviously has mussel power.

Groan.

Yuk, yuk.