• Biology Human Biology The Human Lifespan
  • How long can people live?

    In 2012, the average American citizen was estimated to live to 78.8 years. That’s a relatively long time, but it’s still a far cry from the oldest human on record. Those bragging rights went to Jeanne Calment, a feisty Frenchwoman who died in 1997 at the age of 122.

    Most people will never live for 12 decades. Thanks to advances in the health sciences, though, the average age grows higher and higher each year. But how long can people live for?

    The Hayflick Limit and The End of the Road

    It turns out that there is a limit on how often your cells can divide to keep you young and fresh. This limit, known as the Hayflick limit, is dictated by the physical length of a unique cellular feature called telomeres.

    As Derek Muller explains in How Long Will You Live?, telomeres are the end caps on your chromosomes. They function to keep chromosomes wrapped up tightly in a nice, neat package and prevent them from fraying and binding to all the other little things within your cells. Telomeres are a handy feature, but they also have a downside; each time a chromosome is copied to make another cell, the cellular copying device has to cut off a tiny bit from these end caps.

    Over time, the telomeres get shorter and shorter until eventually they’re no longer there at all, and the cell stops dividing and may eventually die. This is what happens when we age. Among other things, our skin stops replenishing itself, we get wrinkles, and our bones become brittle and frail. We simply wear out.

    It seems like the easy solution would just be to rebuild the telomeres so that they never shorten, thus creating an endless fountain of youth. In fact, there is an enzyme that does just this, called telomerase. This enzyme actually does occur naturally in humans, but not in the most beneficial way.

    Like in comic books where a good scientific premise has gone bad, telomerase seems benign but is actually quite harmful. It does make your cells live forever, but only in the form of cancer. Unfortunately, we currently lack the cellular mechanisms to harness telomerase for good purposes.

    The Immortal Woman

    One of the craziest stories about telomerase has to do with a line of cells called HeLa cells that are currently being used in biomedical research. Rebecca Skloot describes this fascinating story in her book, The Immortal Life of Henrietta Lacks.

    In 1951, an African American woman named Henrietta Lacks felt sick and went to see a doctor. They took a biopsy and found out she had cervical cancer. In those days, scientific ethics were unscrupulous at best, and scientists cultured her cells without letting her know or even asking for her permission. Within a few months, Henrietta was dead, but the cells from her cancer lived on.

    Her cancer cells were unusually prolific and lent themselves well to medical research. Thanks to telomerase, her cells will never run out of telomeres. Given the right environment and enough nutrients, they will live forever. Even though Henrietta’s been gone for a long time, she still lives on in petri dishes and flasks around the world.

    Died From “Natural Causes…”

    Even though there is a limit to how many times our cells can divide, many of us won’t reach that limit. There are myriad ways to die, and only some of them are the result of our cells reaching the ends of their lifespans.

    Up until about a hundred years ago, most people died well before their telomeres ran out due to infectious diseases like tuberculosis and influenza. Thanks to advances in medicine and sanitation, though, it’s pretty rare to hear of people dying from these things nowadays, and as a result, the average lifespan has increased dramatically.

    Still, though, we generally don’t reach the theoretical limit of how long we can live because we’re dying prematurely of other diseases that are a result of damages resulting from less-than-optimal life choices. Now, people are more likely to die prematurely from things like cancer and heart disease.

    While some of these premature deaths are just due to bad luck or less-than-stellar genetics, many of them are preventable through healthy lifestyles. By doing things like quitting smoking, putting down the Twinkies, and using sunscreen, most of us will live to ripe old ages.

    And who knows? Maybe someday we’ll be able to safely harness the power of telomerase so we never grow old.

    What Will You Look Like When You’re Old

    Aging Pic 30 to 60

    Did you know that you can actually predict to some reasonable degree what you might look like when you get older? In 2009, Jonas visited a research institute in Scotland that was doing just that. We made a video on it for our 2010 middle grades series. Even if you’re not a 6th grader, we thought you might enjoy this segment.

    Written by Lindsay VanSomeren

    Lindsay graduated with a master’s degree in wildlife biology and conservation from the University of Alaska Fairbanks. She also spent her time in Alaska racing sled dogs, and studying caribou and how well they are able to digest nutrients from their foods. Now, she enjoys sampling fine craft beers in Fort Collins, Colorado, knitting, and helping to inspire people to learn more about wildlife, nature, and science in general.

    You can follow Lindsay VanSomeren
    Comments