Do Humans Have a Definite Expiry Date? Breaking the 120-Year Barrier
2013 07 10

By Avi Roy | io9.com

In rich countries, more than 80% of the population today will survive past the age of 70. About 150 years ago, only 20% did. In all this while, though, only one person lived beyond the age of 120. This has led experts to believe that there may be a limit to how long humans can live.

Animals display an astounding variety of maximum lifespan ranging from mayflies and gastrotrichs, which live for 2 to 3 days, to giant tortoises and bowhead whales, which can live to 200 years. The record for the longest living animal belongs to the quahog clam, which can live for more than 400 years.

If we look beyond the animal kingdom, among plants the giant sequoia lives past 3000 years, and bristlecone pines reach 5000 years. The record for the longest living plant belongs to the Mediterranean tapeweed, which has been found in a flourishing colony estimated at 100,000 years old.

Some animals like the hydra and a species of jellyfish may have found ways to cheat death, but further research is needed to validate this.

The natural laws of physics may dictate that most things must die. But that does not mean we cannot use nature’s templates to extend healthy human lifespan beyond 120 years.

Putting a Lid on the Can

Gerontologist Leonard Hayflick at the University of California thinks that humans have a definite expiry date. In 1961, he showed that human skin cells grown under laboratory conditions tend to divide approximately 50 times before becoming senescent, which means no longer able to divide. This phenomenon that any cell can multiply only a limited number of times is called the Hayflick limit.

Since then, Hayflick and others have successfully documented the Hayflick limits of cells from animals with varied life spans, including the long-lived Galapagos tortoise (200 years) and the relatively short-lived laboratory mouse (3 years). The cells of a Galapagos tortoise divide approximately 110 times before senescing, whereas mice cells become senescent within 15 divisions.

The Hayflick limit gained more support when Elizabeth Blackburn and colleagues discovered the ticking clock of the cell in the form of telomeres. Telomeres are repetitive DNA sequence at the end of chromosomes which protects the chromosomes from degrading. With every cell division, it seemed these telomeres get shorter. The result of each shortening was that these cells were more likely to become senescent.

Other scientists used census data and complex modelling methods to come to the same conclusion: that maximum human lifespan may be around 120 years. But no one has yet determined whether we can change the human Hayflick limit to become more like long-lived organisms such as the bowhead whales or the giant tortoise.

What gives more hope is that no one has actually proved that the Hayflick limit actually limits the lifespan of an organism. Correlation is not causation. For instance, despite having a very small Hayflick limit, mouse cells typically divide indefinitely when grown in standard laboratory conditions. They behave as if they have no Hayflick limit at all when grown in the concentration of oxygen that they experience in the living animal (3-5% versus 20%). They make enough telomerase, an enzyme that replaces degraded telomeres with new ones. So it might be that currently the Hayflick “limit” is more the Hayflick “clock”, giving readout of the age of the cell rather than driving the cell to death.

The Trouble With Limits

The Hayflick limit may represent an organism’s maximal lifespan, but what is it that actually kills us in the end? To test the Hayflick limit’s ability to predict our mortality we can take cell samples from young and old people and grow them in the lab. If the Hayflick limit is the culprit, a 60-year-old person’s cells should divide far fewer times than a 20-year-old’s cells.

But this experiment fails time after time. The 60-year-old’s skin cells still divide approximately 50 times – just as many as the young person’s cells. But what about the telomeres: aren’t they the inbuilt biological clock? Well, it’s complicated.

When cells are grown in a lab their telomeres do indeed shorten with every cell division and can be used to find the cell’s “expiry date." Unfortunately, this does not seem to relate to actual health of the cells.

[...]

Read the full article at: io9.com




Related Articles
Castration For Longevity? Study examines eunuchs’ longer lifespans
Ecuadorean Villagers May Hold Secret to Longevity
Fountain of Youth in Bile? Longevity Molecule Identified
Aubrey de Grey, Artificial Intelligence, Singularity, Longevity and the Holy Grail
Wadsworth, 27, may be world’s oldest cat
Woman, 116, listed as ’world’s oldest’ dies.
Oldest man in recorded history dies at 116 in Japan
Russian research project offers ’immortality’ to billionaires - by transplanting their brains into robot bodies
2045: The Year Man Becomes Immortal
Henrietta’s ‘Immortal’ Cells


Latest News from our Front Page

Sand Pirates: ISIS Are America’s 21st Century Terrorist Privateers
2014 11 01
What is ISIS? If you believe govt and corporate propaganda, you still think that ISIS is a grassroots Islamic ideological movement ¨C and with no connection to intelligence agencies like America¡¯s CIA, Britain¡¯s MI6, Turkish (NATO) intelligence, Saudi intelligence, Israeli intelligence, or Pakistan¡¯s ISI. The reality of ISIS is something altogether different¡­ On closer inspection, these marauding paramilitary ISIS gangs are nothing ...
Ancient Stone Circles in Mideast Baffle Archaeologists
2014 11 01
Huge stone circles in the Middle East have been imaged from above, revealing details of structures that have been shrouded in mystery for decades. The Big Circle called J1 is about 390 meters (1,280 feet) in diameter, with an open area created by bulldozing in its interior. Credit: David L. Kennedy, copyright is retained by the Aerial Photographic Archive for Archaeology ...
Sweden Recognizes Palestinian State; Israel Upset
2014 10 31
Sweden on Thursday became the biggest Western European country to recognize a Palestinian state, prompting a strong protest from Israel, which swiftly withdrew its ambassador from Stockholm. The move by Sweden’s new left-leaning government reflects growing international impatience with Israel’s nearly half-century control of the West Bank, east Jerusalem and its blockade of the Gaza Strip. It also comes during increased ...
Fed-Backed Study: How to Brainwash Public into Fearing “Climate Change” Like Ebola
2014 10 31
$84K study seeks ways to make public fear "climate change and overpopulation" The National Science Foundation is funding a study to determine how to brainwash the public into fearing “climate change and overpopulation” as if they were Ebola. The NSF awarded an $84,000 grant to researchers at the State University of New York at Buffalo yesterday to figure out how to make ...
Brain decoder can eavesdrop on your inner voice
2014 10 31
As you read this, your neurons are firing – that brain activity can now be decoded to reveal the silent words in your head TALKING to yourself used to be a strictly private pastime. That’s no longer the case – researchers have eavesdropped on our internal monologue for the first time. The achievement is a step towards helping people who cannot ...
More News »