[PBS Intro] Covering a 50 square mile area in Siberia in the Arctic Circle, you'll find a place called Pleistocene Park.

Its human creators have replaced its forests with grasslands to restore the landscape to what it looked like 2 million years ago.

It's currently populated by large mammals like horses and bison to give it that "last Ice Age" feel, but to make it REALLY authentic, they just need ONE more thing... [Intro] Around 4,500 years ago, on an island in the Arctic Ocean, the world's last mammoth died a lonely death.

And now they only live on in our imaginations.

But do they really have to be gone forever?

Humans aren't completely responsible for killing off mammoths, but we are responsible for plenty of other extinctions, and that list is quickly growing.

These species are extinct, but in many cases, their DNA is still around, in places like museum drawers and buried in the ground.

Today, scientists think de-extinction might be the answer to saving our planet's lost biodiversity.

De-extinction is more complicated than it looks in the movies.

DNA holds the instructions for an organism's assembly, life, and reproduction.

By inserting a copy of DNA instructions into an empty embryo, scientists successfully cloned the first mammal two decades ago.

So if we have some of their DNA, bringing back extinct animals is just that easy, right?

Of course it's not that easy!

To make a clone or exact copy of anything, you need a *complete * set of genetic instructions.

Not 50% or 95% of the genetic instructions.

100%.

Imagine the genome as a huge book.

If you lose every 10th word, would you still be able to read the story?

Unfortunately as soon as something dies, its DNA starts to fall apart.

On average, it takes just 521 years for half an animal's genetic material to degrade.

Deep freezing mammoths has improved DNA preservation, but those instructions are still too incomplete to fire up the cloning machine.

To recreate anything remotely ancient, scientists are gonna have to get crafty.

We've gotten a little bit of DNA from several well-preserved mammothcicles.

That let us assemble a whole mammoth genome inside a computer, but we can't just print out a big fuzzy elephant from scratch.

But we might be able to edit one.

Just like you "cut and paste" on your computer, we could snip out certain genes of a close relative like the Asian elephant--and replace them with whatever genetic material makes a woolly mammoth special, like resistance to cold, bigger tusks, and well... fur.

Then, this hybrid embryo would be placed inside a living Asian elephant until it is born, which is a lot harder than it sounds.

For starters, elephant pregnancy lasts more than a year and a half and maybe we shouldn't gamble with a species that's already endangered.

Even if we figure all that out, one mammoth doesn't bring back a species.

Populations with just a few members have low genetic diversity.

Their DNA is almost identical, and this can make them susceptible to disease or even infertile.

Hundreds or thousands of "sort of" mammoths will need to be created to maintain a diverse and healthy population.

But why build something from scratch when you can reverse engineer it?

Believe it or not, the modern chicken is a decently close relative of T. rex.

By carefully controlling the expression of certain chicken genes, scientists have been able to bring out some more "dinosaur-like" features, like turning the beak into something more closely resembling a snout.

Bit by bit this method could create a creature that isn't a chicken, but isn't quite a dinosaur either...sort of a paleontologist's version of Frankenstein.

Hacking elephant genes could give us something that looks like a mammoth, but would it BE a mammoth?

Or just an elephant wearing a disguise?

Even if we COULD bring extinct animals back, it doesn't necessarily mean we should.

Since these animals were around, a lot has changed.

Places like Siberia's Pleistocene Park are trying to recreate ancient habitats, but when these old species arrive at their new home, will the food they once ate even be around?

What about the microbes that helped keep them alive?

De-extinction will be really expensive and really hard.

So why do it?

Maybe instead of paying back the planet for our past screw-ups or just trying to reinvent our favorite movies, we should worry about not making new mistakes.

Instead these new genetic tools could help save animals in imminent danger of extinction today.

Species like the California condor, black-footed ferret, and the adorable vaquita are all on the verge of disappearing forever.

The same technology that makes de-extinction possible could let us add variety to these species DNA, creating genetic diversity, to make their populations bigger AND stronger.

That way we won't be having the same problems 4,000 years from now.