Name: Why We Age - And How We Can Stop It
Uploaded: 2016-10-25T16:24:29.000Z
Duration: 10 min 24 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

More than 150,000 people die on this planet every, freaking, day

and some of those people are getting hit by buses

or dying of how cute a puppy is or something.

their bodies are just succumbing to the dirty work of aging...

and I don't want George R.R. Martin to die before he finishes his Game of Thrones series.

I mean it's something  that we have in common with every other person who has ever lived,

but, some organisms can live to be very, very, very old

and scientists are beginning to understand better how they do it,

and what it might take for *us* to live to be be very, very, very old.

And I'm not just talking about doing squat thrusts or eating kale or whatever.

I'm talking about discovering how our cells die,

and yes , how our behavior influences our longevity

So I'm like "C'mon, scientists! Make me live forever...please?"

Albeit magnificent and really complicated collections

and when it gets too tough for ourselves to keep these masses of cells together...

There's a process of aging that happens over the course of our lives,

culminating in the buying of the proverbial farm.

This process has a lovely little name, it's called Senescence.

And at an organismal level, we see senescence take place after our bodies reach sexual maturity

After that, we begin to lose the ability to combat physical stress, and to maintain homeostasis,

the internal balance of all of our organ systems and body fluid concentrations and most importantly,

we start to lose the ability to combat disease.

'Cause technically, there's no such thing as dying of old age.

This is good news! Not all animals do this! Not all animals age this way.

Some, particularly some cold-blooded animals, exhibit what's called negligible senescence.

They don't lose their ability to reproduce over time, and their death rates don't necessarily increase with age.

These animals basically stay at a certain level of fitness until something terrible happens to them.

Like a disease or predation or a really big, fast truck barreling down the road that they're about to cross.

So, for instance, Galapagos tortoises have been known to live for 170 years

and the oldest quahog clam ever collected was about 405 years old.

Frikkin Shakespeare was writing Hamlet when that clam was born.

Why do some animals get to start to die soon as they reproduce,

but others get a hall pass to near-immortality?

Scientist don't know for sure. They're trying to figure it out by studying senescence at a cellular level.

And it turns out! That our stupid cells have their own deaths programmed into them.

Our somatic cells, the cells that aren't sperm or eggs, are constantly dividing and making copies of themselves

in fact, there are whole armies of cells being made in your body right now.

In the 1960s, the young research named Leonard Hayflick was studying human fetal cells

when he noticed that after a while, human cells just stop dividing and then they died.

He came to realize, that they all quit dividing after about 50 divisions, which took around 9 months.

If you put healthy dividing cells into the freezer, the division would slow down, and even stop

but when he warmed them back up, they'd remember exactly where they left off

and start dividing again until they got to that magic number.

It was in this way, that Hayflick discovered that human cells have death programmed into them.

The number of times a cell can divide is now called the Hayflick limit.

And although it's 50 divisions for human fetal cells grown in a culture,

the number for some animals is less, and for others, it's more.

For instance, mice, which can live for 2 or 3 years, go through anywhere from 14 to 28 divisions.

A Galapagos tortoise on the other hand, has a Hayflick limit of about 125.

So, there may be a correlation between an animal's average Hayflick limit and its lifespan.

But as with everything in science, it is not this simple.

'Cause even though we're always making more, new, duplicate cells,

as we get older, that Hayflick limit gets older.

Studies of people in their 80s and 90s found that their cells only divided about 20 times,

so, since our cells have expiration dates, we in turn, also have expiration dates.

By now, good scientists are asking, "Okay, yes, there's a limit, but what causes the limit?"

Turns out, the answer is probably its chromosomes.

A human cell quits dividing after it stops being able to completely replicate its telomeres.

The little caps of non-coding DNA on the end of each chromosome

that protect the genes from errors and copying.

Telomeres are originally made with the help of the enzyme Telomerase when we're just little zygotes.

But after that every time a cell divides, the telomeres on chromosomes of a new cell are a tiny, tiny bit shorter

A cell reaches its Hayflick limit when the telomeres become so short,

that they can no longer protect the chromosomes and the cell becomes unviable.

So, why don't biologist just fiddle around with our cells and add some telomerase to the mix

so that the cells can keep dividing forever? Well! There's actually a kind of cell that already does that really well.

Cancer cells. Yes! Cancer cells can sometimes create their own telomerase

So that they can replicate indefinitely without their chromosomes getting damaged

which is why they divide like crazy and become tumors.

Because of that, nobody's super anxious to start injecting people with telomerase.

And in fact, one theory is that programmed cell death evolved in order to keep our tissues from undergoing

So. Scenesence. One thing we have to grapple with as mere mortals.

But another thing that's keeping us from playing basketball until we're 500 is our genes.

Here, research into extending longevity has focused on a little nematode called C. elegans.

These little worms are really good test subjects because their lifespan's only about 14 days.

So, scientists have been able to pinpoint the genes that are most likely in charge of aging.