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Life's Limit

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Until Leonard Hayflick came along, everyone thought cells were immortal. That they’d divide over and over again, forever. Hayflick torpedoes that theory and proved that there is limit. A very predictable limit: a magic number. To thank him, science textbooks everywhere now refer to that as ‘the Hayflick limit.’

While Hayflick’s discovery may seem like a buzzkill for those in search of immortality… fear not! Rules were meant to be broken, and Hayflick, now a Professor of Anatomy at the University of California, points out how one might tinker with this limit in the lab…and the potential dangers of doing so. The limit is different, it turns out, for different animals. There are tortoises that live for centuries, and lobsters that seem to be ageless.

Dr. Alexis Carrell on the cover of TIME (September 16, 1935) for finding that “permanent life outside the organism was possible.”

(c) TIME

Carrell performing vascularization at Rockefeller Institute
Lindbergh and Carrell on the cover of TIME (June 13 1938)

(c) TIME

Dr. Carrell giving a lecture
Nobel Scientists Theory on Suspending Life Belittled


Leonard Hayflick

Comments [33]


I'm curious to here more about lobsters that never age. When do they die? What research has been done on lobsters?

Feb. 27 2018 12:43 PM
Paul from St. Paul, MN

Very interesting show. Perhaps the 50 replication limit of cells is related to the general characteristic of cardiac muscle cells in that they can only beat so many times before they are worn out, that and entropy always wins. There are creatures that are potentially immortal: bacteria. Their DNA can divide indefinitely, but their DNA is circular. They also don't have hearts to wear out. But they are under constant attack by viruses. Regarding the previous comment that we are a "horrid generation"; one only need read the book "The Great Big Book of Horrible Things" to discover the 100 worst past events that humans have perpetrated which have resulted in massive number of deaths. This generation is somewhat low on the horrid scale so far (not counting abortions). That book doesn't even deal with all the deaths which were less than 300,000 per event, all the animals people kill, abortions, or environmental damage and pollution people have caused. "To summarize the summary of the summary, people are a problem." Doubling the life span for humans on this planet is probably not the best thing for humans or the planet, but it would be nice to be healthier until one died.

Feb. 26 2018 10:22 PM
Ania from Richmond, VA

This podcast brought me almost to tears. To hear about all the "surgically removed" fetuses while you laugh and Hayflick jokes, right after so many lives where lost at Parkland, was just heart wrenching. Yes, abortion of unborn babies is a choice and killing people in highschool is a choice, and both are absolutely horrid. And if, as you claim, all of us have a part of this unborn child in our veins, through vaccine how much more horrid it is. We sacrifice our own children to better ourselves. We are a horrid generation!!!!

Feb. 25 2018 04:41 PM
Grandpa Dave from Colorado

ditto comment by Katja & Janan. I enjoyed listening to the story and was expecting to hear a connection to the story in the book "The Immortal Life of Henrietta Lacks" by Rebecca Skloot. As I recall, after uterine cancer surgery (1951), her cells were collected by a Johns Hopkins Doc as part of a wide ranging search for cells that can reproduce beyond 50 generations. Her cells were unique and kept regenerating -- hence the name immortal. They were shared with bio labs all over the world and were hugely valuable for developing vaccines, etc. The name HeLa cells is an anonymous label to identify the cells and protect the donor's identify. HeLa cells are still in use today! The book is an interesting read; summary & lots of comments on, and there is a 2017 movie based on the story.

Feb. 25 2018 04:04 PM
CSummer from Virginia

On April 4, 2016, mkham6 posted a tale about a dimwitted BLM "scientist" who deliberately cut down a 5,000+ year old Joshua pine in order to discover its age, and then capped this tale with a nasty remark.

Well, no. I'm afraid mkham6's little tale is inaccurate.

In 1964, geology graduate student Donald Rusk Currey was examining the bristlecone pine trees in California's White Mountains. There's some disagreement as to how exactly it came about, but the end result was that a particular tree was cut down. It wasn't until he analyzed the rings that Currey realized the bristlecone was some 4,900 years old -- the oldest tree recorded at that time.

"The incident led to a tighter restriction on the felling of old trees, the eventual creation of Great Basin National Park (now overseen by the National Park Service), and the decision to hide the exact location of Methuselah, the tree believed to be the oldest at that time. Currey (now a professor of geology) personally took part in lobbying efforts to get Congress to designate the area a part of a national park."

Since then, however, an older tree has been identified in the White Mountains of California. The tree is also a bristlecone pine and is thought to be over 5,060 years old.

Should something happen to that one, Methuselah (a mere stripling of 4,899 years of age) is ready to reassume the mantle of oldest known tree -- but, as Wiki points out, "There is a good chance there are older bristlecone pines that have not yet been dated."

Sources: Wikipedia and the Smithsonian Magazine

Apr. 11 2016 10:16 PM

My subsequent comment is more for the Fountain of Youth story, but applies to this one too.

While diving on the famous verticle Wall (3000 ft drop off from 50 ft) off Cozumel, I came across a humongous lobster, a meter wide, sitting on an escarpment and waving at me arrogantly: "I'm protected, Sparky, beat it.!!" He was- the whole area is a marine park, and since we were diving with dive shops, we couldn't collect/eat anything. I also saw a similar size monster crab, but honestly I wouldn't have touched those babies even if I could- not sure but would guess it was 150 years old, maybe he could have beaten the 50 lb record... and I would never kill something so old (+ wise). The first time in Florida I found myself surrounded by a ring of lobster/crawfish under rocks, I was beset by a deep primal unease- these things were living fossils 400 mil years old.. and I was incompetently trying to pull them out by accidentally ripping off their antennae. Ow-ow. Revenge of the ageless timeless crustaceans from antiquity.

Speak of which, did anyone hear the story of the dimwitted BLM "scientist" who wanting to date an ancient Joshua Tree Pine, cut the whole thing down, returned to his lab, and discovered he had killed the oldest living thing on the planet: ~5000 years. There must be a place in hell for that guy.

Apr. 04 2016 09:04 PM

Hmm, gotta listen to this one again. Amazing show- immortality genes, but somehow think humans shouldn't have that capability (except for space colonists) with 8 bil humans destroying the planet. If anything, maybe we need a 50 year "replicant" life limit, like in Blade Runner. The Chinese were trashed for their one child policy but if they were now 2.5 billion people, they would be creating 80% of the GHGs and waste and still living in misery.

There should be a strict limit on children, esp among Muslims, Indians, Catholics who have litters of kids to provide their Social Security and ensure their legacy. Maybe 1 child per 2 families, done by lottery- with financial or benefits penalties for violation.

Apr. 04 2016 08:07 PM
Sue from Beltsville, MD

To Jack regarding his comment about telomeres: You are correct that telomeres function in limiting the number of times a cell can divide. However the question was not "How" cell division was limited to that number, but "Why". We still don't know why that particular number was chosen.

Apr. 04 2016 01:29 PM
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Nov. 21 2014 11:43 AM

I just discovered Radiolab last week, and this was the first story I heard, which was fascinating to me. Back in 1990 I was a lab tech at MD Anderson cancer center in Houston, Tx, and I loved it, my job was tissue culture, and yes at times the cells I took care of did die, some flasks got contaminated, and the lab was used by many people, we were a group of 25 students, post docs and techs, so it was difficult to control all the conditions for these cells, but now I know that one other possibility was that these cells could have reached their end. The 2nd show I listened to was the famous tumors, and that also hit close to home, for I also remember having worked with the Hela Cell line, and all I knew at time was that these came from a lady named Henrietta, so it was nice to hear the rest of the story so many years later. I am now hooked, thankful for all the podcasts, for every night I find myself mesmorized, stimulated and enlightened by all of your beautifully told stories, I might add that your music in the stories adds another dimension to each story, making more enjoyable, thank you.

Jan. 21 2013 01:44 PM
jack from FL

Hayflick was asked "Why 50 times?" To which he replied, "You'd have to ask god." Apparently God is the name of the scientist who studies telomeres. Telomeres are at the end of chromosomes and due to the nature of DNA replication, get shorter every time until they can't replicate again.

Jan. 14 2013 08:33 AM

Great podcast, thanks!
I was anticipating the story of Henrietta Lacks and the HeLa cells which would fit very nicely here but it may become a different episode.

Jan. 13 2013 07:52 AM
leah zueger

I found the Mortality show interesting but hard to stomach when it was stated that an aborted 'child' resulted in vaccines. It was instead, an aborted fetus. I hate to think I would have to go into details about the difference between a child and a fetus. It's difficult to believe that no one editing this segment caught that 'error'.

Jan. 12 2013 04:43 PM
Victoria M from HFA

This was so interesting. I've been waiting to learn about the human anatomy for awhile now and I forgot how it starts with cells, being the smallest part of us. What was most interesting (the part I learned from this podcast) was freezing the cells to save them. I didn't know they'd work afterwards. Also, taking cells from anywhere to replicate them is something I sort of knew but learned more about. They only question I really have is since the cells slow down with the lower temperatures, do people who live in really cold places, like Alaska, age slower than people who live in warmer temperatures?

Oct. 07 2012 10:45 PM
Hope B White

No, not weird, Eric. Just the kind of mind that not only stays on track but has practically created the track. It's called "genius."

Sep. 28 2012 08:42 PM
Eric C from Henry Ford

As i listen to this thinking that it was going to suck, i found it very intresting. for instence when they talk about the cells an how when they divide they could cover new york in 3 weeks. i learned that after when cells freeze they still continue to multiply. something intresting that raised questions for me was the quotes they said just because i could barley understand it. im just going to throw this out there but did anyone find the guy keeping the cells inside his garage kind of weired... not caliing him weired just the idea of it is weired.

Sep. 27 2012 09:40 PM
Mario Walle

As I don't like being hypocritical the truth is that I don't like this class because is hard, but it is my responsibility to do the homework. So I learned that the cells are not immortal and that when the temperature is low cells work slower and in the contrary of this when the temperature rises the cells work much faster.I also learn that the cells in a fetus could provide vaccines for a billion people.Just to end i just wanted to add that they mentioned a great word that starts with F.

Sep. 25 2012 10:16 PM
Yukki G from HFA

What I found interesting was the fact that they compared science to witch craft. That was pretty cool. What is also interesting is that a simple skin sample you give, or shed, can multiply and continue to divide even after being frozen, they continue to divide and function as if nothing affected the. What determines the cells life? why do certain animals live longer than others? that still baffles me.

Sep. 25 2012 09:14 PM
Sidney F from Henry Ford

I learned mainly a lot more about cellular division by listening to this podcast. You could take a piece of your skin from anywhere, your feet, hands, etc.., and use that to divide cells. After the cells divide so many times it stops, but yet when freezing the cells over time they will pick up and continue where they left off. This is what i found interesting. How you could lower the temperature these cells are stored in to the point that they freeze over many years, and they still continue to divide where they left off when they return to their original environment. Why were the aborted fetuses more rational for his experiments? What is the purpose of our cells dividing? I know they keep us alive but what can you tell about our body from the division of our cells? If cells were our only source to live by, if you froze a body, and then defrosted it would we continue to develop and grow?

Sep. 25 2012 01:30 PM
haley s from HFA

from listening to the podcast i learned that the devision of cells will stop when the temperature is brought down to a certain point, allowing the scientist to save them essentially forever. also that the scientist mentioned in the pod cast was able to help with creating vaccines with his frozen cells, and that after a certain number of devisions the cells stop to divide. i thought that the cells stopping devision at a certain point was interesting also that in order to achieve "immortality" we would have to take the consequence of cancer. some questions i had were why the use of aborted fetus cells was not really practical or allowed. also what do the cell devisions mean? is that our aging? does it occur only in the first nine months of life or does it continue throughout our life?

Sep. 25 2012 01:19 PM
Elisheba from HFA

I thought this wass soo cool! I'm getting to school late because I wanted to hear it all! I found this interesting to find out how the fetal cell could multiply and keep on...also to find out that vaccines could become from just one cell. about abortion I just think that people make their own decisions, if there wasn't abortion then would the population be too much? not saying I'm for it but this helps with the limit of people. We will never be able to make someone change their frame of thinking unless they were open to it.

Sep. 25 2012 09:53 AM
Keren H from Henry Ford

What I found interesting/creepy was that the scientist dressed in all black.. Another interesting thing is how cells could just keep dividing for as long as possible, which is 50 for some reason. Just.. another creepy thing is that the guy would order aborted fetuses. Okay, I just find this podcast more creepy than interesting really... So the only reason a cell would seem to be immortal is if you freeze them? But unfreeze them and then they'd just continue on where the left off.. until they reach 50... So is it possible that a lobster could maybe grow into the size of a medium-large animal?

Sep. 25 2012 02:48 AM
Mitchell L. from Henry Ford

This certainly was an interesting podcast to listen to. I found the human/animal cell division possibly determining how long something lives to be interesting, as well as the, "magic number."
I didn't know that lobsters could possibly live longer than we can measure, and find that pretty interesting. Also how cell division can be stopped with harsh cold temperatures and be resumed by cooling them down.
These make me wonder, what could we learn from lobsters? Could we find out more about cell division from them? And if a human were to somehow be able to survive in a beyond freezing environment, would that human live longer than the average human?

Sep. 25 2012 02:04 AM
Forest R. from Henr Ford

The things I found most interesting were the cells used from the fetuses to find out about the 50 cell division limit, and the fact that the enzyme that would allow immortality would have the cost of cancer. This podcast was very enlightening to me. I found it mind blowing to know that cells from one fetus could supply vaccines for a billion people.

Sep. 25 2012 01:15 AM
Monique D. from Henry Ford

I found this to be interesting because I didn't know very much about this topic.( I also thought the sound affects were cool) I learned that cells have a limit when it comes to dividing. I heard that abortions were more rational. That raised the question, why? Also, what makes tortoises so special? Why do they get to live so long?

Sep. 24 2012 11:27 PM
nick from Henry ford

This was interesting. Cell research is a major topic and to find out there is a limit as well as a way to alter limits is quite astounding. I didn't know much about this until I came across this for school.
I wonder how things will change if and when it is for human use.

Sep. 23 2012 08:16 PM
Kenton from San Diego, CA

Just heard this on San Diego's KPBS.... I was floored by this story. Thank you so much for excellent journalism.

Feb. 04 2012 08:15 PM

Everything is a choice. Every single thing in life is a choice.

Stem cell research has made such huge scientific leaps of progress. Stem cells are not humans, they just have the potential to become humans. Its similar to many religious beliefs that any protected sex is wrong.. it too is inhibiting life to form.

Does the benefit out way the means? Cure hundreds, thousands, maybe even millions from cells. Yes.

Sep. 28 2011 10:22 PM

abbortion is a choice every choice can be rational and irrational it depends on the state of mind

so if one decision is rational it doesn't mean the opposing choice isn't

Oct. 04 2010 07:26 AM
David Kleinschmidt

Did I hear you say abortion is "rational"?
So logically, those that respect the rights of the unborn are "irrational"? Seems to me science supports the fact that a "fetus" is a human.

Sep. 26 2010 12:57 AM
Margelit Hoffman from Jerusalem, Israel

Is there no connection between 50 fetal cell divisions taking 9 months and the 9 months of pregnancy?

Feb. 11 2010 05:54 PM
Josh from San Diego CA

I would like to second Angie's comments. I have used WI-38 cells in my own research never knowing that this was the same cell line in which Leonard Hayflick first observed his eponymous limit. It was a thrill to hear his story... from him! Great podcast; it makes commuting fun.

Sep. 19 2007 12:51 AM

THANK YOU so much for having Leonard Hayflick on your show. He has been one of my scientist heroes for a long time, and is the reason I am working in cellular aging. Each one of your episodes seems eerily entwined with my particular research interests. three cheers for this podcast

Aug. 16 2007 12:49 PM

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