What if we could be biologically immortal like a hydra,

a tiny freshwater creature that can continuously renew its cells?

Or what if we could turn back the clock like some jellyfish that never die

but revert to an earlier form and go through life all over again?

But most cells in our body aren't built to last a lifetime.

They're damaged all the time by everything from ultraviolet rays to poor nutrition.

When this happens, cells make copies of their chromosomes,

which contain our DNA, and divide into healthy new cells.

But at some point, cells lose their ability to replicate.

With each cell division, the ends of our chromosomes get a bit shorter.

These end regions don't actually hold active genes.

They're protective caps called telomeres.

But once telomeres shrink past a certain point,

the cells can't divide anymore and enter a state called senescence.

There's nothing inherently bad about cells becoming senescent

Senescent cells just behave differently from cells that can still divide.

They also secrete a variety of chemicals that activate the immune system.

When we're young and healthy,

this can help us recover from injury, for instance.

But the issue is when the body doesn't eliminate senescent cells quickly

enough and they make neighboring cells go senescent as well.

That begins a domino effect that can lead to chronic inflammation.

Over time, this makes our brain work

slower and causes our body to start to deteriorate.

We become more susceptible to disease and we die.

But does it really have to happen this way?

Experts have a lot of theories about why we age.

One of the most popular ideas is that human bodies

only have a limited amount of lifetime energy, and we spend lots of this

energy prioritizing reproductive functions.

Scientists call this the "Disposable Soma Theory." The idea is that our

soma, or body, is disposable while our germ line lives on.

Not everyone wants to reproduce, though.

For those who would prefer a few extra years to having children,

there may be ways to shift your body's energy allocation,

decreasing your fertility to extend your lifespan.

But if everyone could suddenly choose between fertility and long life,

it could lead to a host of ethical issues.

Whose lives are extended and who can reproduce?

And if you try to reach a sort of compromise,

extending your lifespan while still having kids, you might just end up

increasing your children's or grandchildren's risk of mutations,

which could end up causing major issues in your descendants.

It's hard to fight aging because it lies at the very core of our genetic makeup.

Short telomeres would be an obvious target for anti-aging interventions.

But people with very long telomeres or more telomerase, an enzyme

that keeps telomeres long, aren't always better off.

Cancer cells can use telomerase to multiply unchecked.

And people with excessively

long telomeres may be likelier to get lung cancer and brain tumors.

Some researchers are trying to prevent cells from reaching senescence

or to help the body remove senescent cells more efficiently.

But they face a similar problem.

They need to target specific cells that induce aging

and avoid ones that are benefiting the body.

Researchers still have some ideas for extending lifespan though.

Among the most popular is moderate caloric restriction.

In one study, people who ate 15% fewer calories for two years ended up with a

significantly lowered base metabolic rate, an indicator that their body aged less.

But this has to be done very carefully because the body needs

nutrients to survive and function properly.

And while some caloric restriction may extend lifespan, scientists

are still investigating whether it could lead to unintended side effects.

For instance,

animal studies suggest under-eating may decrease gray matter in the brain.

Though it doesn't necessarily mean it hurts mental performance.

Perhaps, though, longer life isn't the right target.

Instead, many researchers are turning their attention to giving people more

healthy years, something that's remained a challenge despite medical advances.

Chronic diseases are on the rise globally, posing a major strain on health

resources and national economies as people live longer.

At this point, there aren't many innovative ways to extend

your so-called "healthspan" besides obvious factors,

such as maintaining a balanced diet, exercise and strong social connections.

Beyond that, aging is built into our DNA.

And while experts are continuing to explore clever ways to counteract it

at a molecular level

through drugs or other therapies, our body is never going to be permanent.