Nature's guide to immortality
Ageing apes, ancient clams and a jellyfish that never dies reveal how some species attempt to extend their own mortality.
From the moment they are born into the dense jungle of Central Africa, the biological clock is ticking for baby bonobos. A recent study, published in the journal Science, revealed that all primates - from men to monkeys - roughly age in the same way, with a high risk of dying in infancy, a low risk of dying as juveniles and then an increasing risk of dying as they aged.
Some species though, have found a few tricks to help them play the aging game and extend their natural lifespans.
By doing so, they can live for hundreds of years.
A select few, by some definitions, may already have become immortal.
Small to big
Naked mole rats
- Live up to 24 years
- Form eusocial communities like ants, bees and termites
- Each colony has a 'queen' rodent that produces all the offspring
- The rest are sterile helper rats that serve the colony, in a similar way to worker bees
- They are native to arid areas across East Africa
Most of our knowledge about how animal species age comes from studies on short-lived species such as fruit flies and mice.
Laboratory research has shown that altering single genes can extended the lifespan of species of worms and fruit flies.
For example, two years ago scientists from the Brown University in the US doubled the average life span of a fruit fly from 35 days to 70 days by altering the indy gene which reduces the production of free radicals.
But even this doesn't match the capacity of wild animals and plants to embrace a long life.
Generally speaking, larger animals live longer than smaller animals.
On average, a mouse may live for two years, whereas bowhead whales may live for over 200 years.
These differences arise due to a number of physiological differences, including rates of growth and development, metabolism and details of body composition.
However, some species can take special steps, either by changing their behaviour or physiology to grow older than they might otherwise.
Naked mole rats lives 5.3 times longer than expected for their body size, a feat that has attracted increasing scientific attention in recent years.
It isn't clear how they do it, but studies by Professor Rochelle Buffenstein and colleagues from the University of Texas Health Science Centre in the US, suggest that living underground helps.
This might help limit the rodents' exposure to light and helps them avoids dangers that could kill them at a younger age.
Communal living may also reduce their chances of dying, while the animals have strong immune systems and are not known to develop cancer.
These factors mean the mortality of naked mole rats does not appear to increase with age, allowing them to evolve genes for longevity, Prof Buffenstein told the BBC.
Little brown bats
- Brandt's bat (Myotis brandti) can live up to 41 years
- Male bats are generally longer-lived
- Hibernation extends the life of bats by up to six years
Other animals also spend most of their lives in the dark, including some species of bat that can live for decades.
Reducing the time spent in sunlight helps minimise exposure to UV radiation, which creates free radicals known to damage and age tissues prematurely.
Bats also spend a lot of time in a state of torpor.
But bats do more to slow the ageing process than sleep.
Dr Asish Chaudhuri from the Sam and Ann Barshop Institute for Longevity and Aging Studies in San Antonio, Texas, believes the explanation may lie in the way bats protect themselves from protein damage, using special molecules called protein chaperones.
"Proteins play an essential role in virtually every cellular function," Dr Chaudhuri told the BBC.
Proteins have a particular shape, and if they become misshapen, then they do not function very well. But it "can also result in the formation of toxic protein aggregates associated with ageing and several age-related diseases", he says.
Bats are not alone in their drive to protect themselves from protein damage.
Studies of the American lobster (Homarus americanus), have shown that its extreme longevity might be related to the expression of telomerase, the enzyme responsible for repairing small sections of DNA.
High concentrations of telomerase are found in cells that need to divide regularly such as organs and embryonic stem cells.
Access to an elevated supply of telomerase would equip this crustacean with the ability to rebuild cells damaged by aging.
The ability to repair cells in this way may help to explain why lobsters can live up to 100 years and are able to regrow limbs even at an "old age".
An alternative theory suggests attacks by free radicals may be the main driving force behind ageing.
Another oceanic resident, the quahog clam (Arctica islandica), is thought to be one of the longest lived metazoans of all.
"The reasons for the exceptional longevity in Arctica may have little to do with resistance to oxidative stress, though," Dr Iain Ridgway told BBC News.
Instead, as with naked mole rats, it may be the integrity of the animal's proteins that may be the key, rather than damaging free radicals or antioxidants used to defend against them.
Plants may be even more capable of extreme longevity.
The oldest tree in the UK is an ancient yew estimated to be between 4,000 and 5,000 years old.
Some species, like the naked mole rat, also benefit from a form of group living.
Some trees, for example, are actually interconnected underground via a complex, colonial root system.
One such group of trees, nicknamed the Pando, or the Quaking Aspen of the Colorado Plateau, has a living root system that is estimated to be in excess of 80,000 years old.
The massive root system underpinning the Quaking Aspen colony allows it to withstand frequent forest fires and store vital water and nutrients for sustained growth, and a ripe old age.
- Hydrozoans are small animals that can exist as polyps, individually or in a colony
- A jellyfish is the reproductive phase of the polyp which releases eggs and sperm
- The fertilised eggs develop into larvae that settle on the sea bed, transforming into polyps
- The polyps reproduce asexually, producing a new colony or jellyfish
But it is not a land dweller that appears to have achieved eternal youth.
The answer to immortality may actually live below the waves.
The hydrozoan Turritopsis dohrnii has a life cycle that allows it to revert back to an earlier stage of development - essentially turning the clock back on ageing.
"Normal jellyfish die after reproduction. Turritopsis dohrnii jellyfish, however, when facing adverse conditions such as physical damage or starvation, instead of dying, sinks on to the bottom," explains Dr Maria Pia Miglietta, a marine biologist from the University of Notre Dame, Indiana, US.
"They become a ball of cells, rearrange their cells through transdifferentiation, and become a new polyp. That new polyp in turn can produce new polyps and form a colony."
During the right season, the new colony will produce several new jellyfish - and so the rise of the immortal begins.