As old as time

Oldest living things in the world

There are some staggeringly old living things on earth. This article will explore these organisms, although the definition of "oldest" can vary according to how you look at it.

This Gala´pagos Island giant tortoise may live, like Harriet, to about 176 years or even longer. CHILDZY

Various criteria can be used to categorise the oldest living things, which make direct comparisons difficult. One criterion I will use to assess the oldest living organisms is the period from conception to death, a single lifetime during which cells don't divide any more due to DNA (deoxyribonucleic acid) damage. This is essentially the definition of ageing. Other criteria include the existence of living colonies and the maintenance of life during suspended animation.

Oldest living animals

There is an interesting theory that says that every mammal has a certain number of heartbeats in its life, and that figure is approximately the same for all mammals. This is the reason why mice live for about 18 months and elephants live for about 70 years, as long as in both cases they avoid disease, predation, drought and famine.

When you consider that the average heart rate for a mouse is around 500 beats per minute and roughly 30 beats per minute for an elephant, this hypothesis kind of makes sense, but how true it is I do not know. It is a nice theory, though!

When it comes to mammals, the rule of thumb is, the bigger you are, the longer you live. Whales, the largest and longest-living mammals, have extremely long lifespans, whereas mice, rats, moles and voles all have very short lifespans.

Humans are a little different as they have long lifespans relative to their size, but this is only on account of our increased health awareness and medicinal knowledge. A mere 100 years ago, a human was lucky to reach 45, which is much more realistic if our size is used as the basis for assessment.

The same extended lifespan is afforded to animals in zoos. Lack of competition for food, the absence of predators and the availability of veterinary health treatment result in zoo animals generally living far longer than their counterparts that live in the wild. Indeed, the oldest chimpanzee in captivity has made it into the 70s, whereas in the wild the lifespan of a chimp is only about 40 years.

But mammals don't live to be the oldest in the animal kingdom. Macaws regularly live from 70 to over 100 years! Reptiles also have stunning longevity.

Harriet (Nov 14, 1830 _ June 23, 2006) was a Gala{aac}pagos tortoise (Geocheloe elephatopus porteri), originally thought to have been taken from the Gala{aac}pagos by Charles Darwin and that lived at Australia Zoo, the home of wildlife warrior Steve Irwin, died four years ago at a staggering 175 years of age! See happy Harriet on page E1.

Long live the quahog! And Harriet wasn't the oldest tortoise, as other species have lived to over 200 years of age. But even these lengths of time aren't record-worthy when compared to the lifespan of the ocean quahog (Mercenaria mercenaria), a bivalve mol-lusc. The popular name comes from the Narragansett (a northeastern American Indian tribe) word "poquauhock". Like trees, ocean quahogs produce one ring for each year of life, and they have been known to live to over 400 years in the wild! There are other contenders, and it is certainly difficult to arrive at a consensus, but the ocean quahog has my vote for the oldest living animal.

Plants

When it comes to ageing organisms, plants are the true champions. Many plants are thousands of years old based on ring counts. The oldest single living tree is a bristlecone pine in North America fondly named Methuselah. It is dated at being over 4,700 years old, and is so special that its actual location is kept secret.

Ageing colonies

These hard shell clams, aka ocean quahogs (‘Mercenaria mercenaria’), show off their distinctive ‘tree rings’ that are used to establish their age, which can reach over 400 years! KEN HAMMOND

Many plants, fungi and bacteria species reproduce asexually by cloning. This allows clonal colonies to live to exceptional ages, although the individual clones do not live very long.

Examples of long-living clonal colonies include a huckleberry bush in the US which has been around for 13,000 years and counting. In Tasmania, a plant of the species King's Lomatia is thought to be over 43,000 years old! From the first plant, it has continuously, vegetatively cloned and has been in existence for 43,000 years since the very first organism took root.

Interestingly, because the species is sterile, this one cloned colony is the only King's Lomatia cluster alive. As long as conditions are right, the trees will keep cloning, expanding the colony and continuing to exist. Each individual plant has a lifespan of no more than 300 years old, but, because the species has been cloning itself for an incredibly long time, collectively the colony is truly ancient!

Ancient legacies

The Daintree Rainforest in Northern Queensland in Australia has been in existence for over 130 million years, making it the oldest rainforest in the world and a very special biological area. Although no individual tree is anywhere near that old, the forest itself is incredible in its relatively unchanged longevity.

The best way to ensure longevity is by "suspended animation", a trick that bacteria have mastered. In 1999, a bacterial sample found in ancient sea salt in New Mexico was living in stasis. Scientists managed to revive Bacillus permians, therefore effectively bringing it back to life.

The sample was dated at an incredible 250 million years old, officially the longest-living thing ever. Through being revived, Bacillus permians was able to replicate and continue living and, hence, it has never died.

What is the future for human ageing?

Senescence is the science and study of ageing, in which cells' loss of ability to replicate properly is studied. Why this phenomenon happens is still relatively unknown, but no one really ever "dies of old age". As you age, you lose the ability to combat disease, or you may suffer organ failure or you may develop cancer. These are some of the reasons for why you die, but all of these are certainly a result of ageing.

Changes in our diet, fitness and supplement intake may help to slow the ageing process, but it is still an inevitability. Scientists are now trying to prolong or prevent ageing through tissue rejuvenation and stem cell technology, and certainly future generations will live longer.

Suspended animation, wherein humans are cryogenically frozen, may be the only way to truly live for centuries, as long as you get woken up!

A tiny, green plant-like animal called a hydra is thought to be potentially biologically immortal as it apparently does not undergo the ageing process. Will humans ever capture this ability?

I personally think it is unlikely, and, as Freddie Mercury of the English rock band Queen once asked in a song, "Who wants to live forever?" Not me, that's for sure!


Dave Canavan has an MSc in Behavioural Ecology and is the Head of Secondary at Garden International School. Dave is fascinated by science and loves animals, especially the dangerous kind! Contact Dave at

davidc@gardenbangkok.com .

About the author

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Writer: David Canavan
Position: Writer