Let me guess: You’ve probably never heard of the Hayflick limit. No shame in that. I probably wouldn’t either, except for the fact that it was discovered by the father of one of my Hershey classmates, Susan Hayflick. A molecular geneticist in her own right, Susan is currently on the faculty at Oregon Health Sciences University (OHSU). Her dad Leonard passed away earlier this month, and he was – just no other way to put this – truly immortal in the field of molecular genetics. The times story is here. Susan’s OHSU blurb is here.
Susan’s other claim to fame is that it’s her own embryonic stem cells that serve as a basis for the WI-38 cell line that has been used for decades in making vaccines against, among other things, pneumonia. Talk about a lasting legacy. But more on the details of her dad’s groundbreaking research into cellular aging below.
********
Like many great scientific findings, Dr. Hayflick’s came somewhat by accident. As a young scientist in the early 1960s at the Wistar Institute, a research organization at the University of Pennsylvania, he was trying to develop healthy embryonic cell lines in order to study whether viruses can cause certain types of cancer.
He and a colleague, Paul Moorhead, soon noticed that somatic — that is, nonreproductive — cells went through a phase of division, splitting between 40 and 60 times, before lapsing into what he called senescence.
As senescent cells accumulate, he posited, the body itself begins to age and decline. The only cells that do not go into senescence, he added, are cancer cells.
As a result of this cellular clock, he said, no amount of diet or exercise or genetic tweaking will push the human species past a life span of about 125 years.
This finding, which the Nobel-winning virologist Macfarlane Burnet later called the Hayflick limit, ran counter to everything scientists believed about cells and aging — especially the thesis that cells themselves are immortal, and that aging is a result of external causes, like disease, diet and solar radiation.
Other researchers later discovered the mechanisms behind the Hayflick limit: As cells divide, they create copies of DNA strands, but the ends of each copy, called the telomeres, are a bit shorter than the last. Eventually the telomere runs out, and the cell stops dividing.
Dr. Hayflick made other important contributions to science. He developed a particularly vibrant cell line, WI-38, which has been used for decades to make vaccines. He also discovered that so-called walking pneumonia, unlike regular pneumonia, is caused not by a virus but by a type of mycoplasma, the smallest form of free-living organism.
But it was his work on aging that established his legacy. Dr. Hayflick was an outspoken critic of those who thought they could unlock the science of eternal life; he considered that idea an illusion and the pursuit of it a folly, if not outright fraud.
“The invention of ways to increase human longevity is the world’s second-oldest profession, or maybe even the first,” he told the medical journal The Lancet in 2011. “Individuals are going to the bank at this moment with enormous sums of money gained by persuading people that they’ve found either a way to extend your life or to make you immortal.”
********
So then, there you have it:
There’s no fountain of youth.
125 is humanity’s upper age limit.
And you can say you heard it here first.