Be Smart

- Hey, smart people.

Joe here.

I need someone to explain this, because these fruits don't make any sense.

Let me show you what I mean.

(engine revving) No seeds.

I mean, the whole point of a fruit is to help a plant spread its seeds, right?

Fruit tastes good, animals eat fruit, seeds get dropped, new plant grows, which grows more fruit (clock ticking) and the circle of life keeps going.

But these fruits here don't have any seeds.

They've forgotten the whole point of being a fruit.

And the only reason they exist is us.

See, without our help, none of these could continue to survive.

Seedless fruit is the biggest paradox this side of the produce section.

Today we're gonna explore how and why these even exist.

How did humans learn to hack plant reproduction?

What does it mean to create life forms that literally can't exist without us?

And why is every banana you've ever eaten actually a ticking time bomb?

(clock ticking) (mysterious music) Think about it.

When was the last time you bit into a banana seed?

I'm betting never.

And while we're at it, I bet most of the citrus, the grapes, watermelons that you've munched on have been suspiciously seedless too.

But it wasn't always like this.

I mean, I'm old enough to remember picking those annoying little seeds out of oranges, seeing who could spit watermelon seeds the farthest.

You could take your seedless fruit, and get off my lawn.

Today, a majority of the fruit that we consume, at least here in the US of A, is seedless.

80% of the grapes not grown for wine don't have any seeds, and seedless tangerines make up about half of all the citrus that we eat in the US.

And I mean, it's not really a mystery why.

Seeds are annoying, and people like to buy things that aren't annoying.

And since farmers and plant breeders like money, (farmer cheering) they're incentivized to make more and more seedless varieties so that we'll buy more and more of them.

Convenient for us, but inconvenient for plant reproduction.

Plants have spent millions of years evolving a tried-and-true process for keeping their various species going.

Pollinators, like bees, birds, even the wind, help pollen from the male parts of a plant's flower reach the female part of the flower.

This is what your parents should have told you when they gave you the talk about the birds and the bees.

Once the pollen hits the flower's female bits, it fertilizes the flower's egg cells, eventually developing into seeds.

Plants want to make sure that their seeds get scattered around so their offspring have a better chance of survival.

And they've developed a lot of pretty crazy ways to literally sow their oats.

Fruiting plants rely on temptation to spread their seeds.

As their fertilized seeds develop, the tissue around the seeds starts to grow.

It may become hard like a nut, or squishy and sweet like fruits, but the goal is all the same: Convince some animal to eat the seed, and drop it somewhere else so that a new plant can grow and start to process again.

But, you see, plants aren't perfect.

Sometimes the reproductive programming goes a little haywire or gets mutated, and a plant grows a fruit without a baby plant seed inside of it.

That's what happened a century ago in Brazil.

A group of monks were chilling in their orange grove and stumbled upon one branch of one orange tree that was pumping out seed-free fruit.

A miracle!

(glorious music) Well, actually no.

What they'd really found was what we call a bud sport.

That's what happens when the cells of a specific plant bud, like a branch or a flower, get spontaneously mutated.

And depending on where the mutation happens, this can lead to a flower that's a different (computer warbling) shape, or color, or a tree branch that's loaded with fruit that has different characteristics or phenotypes from the rest of the plant.

So on these monks' orange tree, a random bud sport had its gene scrambled in just the right way.

And instead of going through the normal pollination thing, this mutant branch started producing fruit (computer warbling) all on its own, no fertilization required.

Scientists have a fancy name for this: parthenocarpy, which literally means virgin fruit, which when you think about it, is very appropriate for a seedless fruit found at a monastery.

Though the monks were like, "This is delicious, we want more of this," (monks cheering) but without seeds inside to grow a new plant from, how are you gonna do that?

Grafting.

That's how.

You take a twig or scion from that seedless mutant branch and splice it onto some ordinary orange tree roots.

The result is a Frankenstein's monster of an orange tree.

By doing this over and over, taking copies of copies and grafting them onto ordinary roots, the monks created more and more cloned trees, and sent them around the world.

That original monastery mutant was the parent of every Navel orange you've ever eaten.

Think about what that means.

Those oranges, along with seedless cucumbers, grapefruits, figs, bananas, they all would've ceased to exist when their mutant parent plant died.

It has taken immense human labor and effort to keep these impossible fruits from disappearing forever.

Because without us, that's what would happen.

But parthenocarpy isn't the only way to get seedless fruit.

Next time you bite into a grape, take a look inside.

They are seedless, but there's like a little something inside.

Those are what should have been fertilized seeds.

But they never fully developed, thanks to a genetic error called stenospermocarpy.

So back in the 1950s, a Japanese scientist treated watermelon plants with a chemical called colchicine.

Those chemically treated watermelon plants ended up with four sets of chromosomes, instead of the usual two sets.

Having more than the usual number of chromosomes is called polyploidy.

Having more copies of genes than you're supposed to can cause a whole host of malfunctions.

But plants seem to be weirdly tolerant of having extra pairs, and farmers have done something cool with this trick.

A watermelon plant with four sets of chromosomes grows flowers like normal.

Those get pollinated with pollen from a normal plant with two sets of chromosomes.

Now, because gametes each have half the chromosomes of their parents, the fruit that begins forming has three sets of chromosomes.

The juicy, red, sweet part of the fruit keeps growing like normal.

But when the plant detects an odd number of chromosomes in the developing seeds, (alarm blares) it pushes the mutant emergency button, and those seeds stop growing.

That's why seedless watermelons have those little like half formed, not quite seed things.

Now, if it sounds like we're messing with Mother Nature in some pretty weird ways, it's because we are.

But humans have been manipulating plants for thousands of years.

It's literally what gave us agriculture and modern civilization, and we're still at it.

We use hormones to make plants grow bigger, (apple grunts) and keep veggies fresher for longer.

We've even done atomic gardening, shooting plants (laser zaps) with radiation to make mutant desirable features, like this super red grapefruit.

And now with gene editing technologies like CRISPR, scientists can surgically cut and paste DNA to help us get the characteristics that we want faster and more precisely.

There are companies already working on CRISPR-engineered seedless blackberries, and tomatoes, even taking the pits out of cherries.

The future's gonna be weird, man, but when you take the seed out of a fruit, the very thing the fruit evolved to carry, what does that fruit become?

Every single seedless plant we've ever cloned or grown without our help would just die out.

Humans are the first species in the whole history of life on earth to create new species that completely and totally depend on us to survive.

Does that make us gods?

(lightning zaps) Ah!

When a system requires constant babysitting to keep it from falling apart, that's called a maintenance trap.

In 2024, a miscoded software update sent more than eight million Windows computers around the world spiraling into that blue screen of death.

Banks couldn't process transactions, hospitals couldn't access patient records, and airports ground to a halt.

When we create systems that are dependent on us constantly fixing them and taking care of them, they can fail spectacularly.

Broken software is one thing, but creating living things at risk of dying, that seems different.

But then again, maybe seedless plants aren't exactly alive.

In most biology textbooks, you'll find a list of characteristics for living things.

You've gotta have a stable structure, consume energy, grow, respond to stimuli, adapt to the world around you, and reproduce.

Plants that make seedless fruit hit all of these requirements except one.

They can't reproduce, at least not in the usual way.

So does our definition of life need adjusting, or are seedless clones something else entirely?

Every banana you've ever eaten is a direct copy of some other banana, cloned and replicated by the billions, like tiny yellow simulacra detached from their original source.

Now, filling fields and shells with genetic clones has helped feed billions of people, and well, they taste great.

But creating all these plants that are genetically identical comes with risks, because clones all have the same Achilles' heel.

That's what happened with this banana.

70 years ago, this was basically the only banana you could buy in the United States.

But today, it's almost extinct.

This super rare banana is a Gros Michel, AKA, the Big Mike.

I don't just have giant hands.

This Big Mike's just not very big.

It was ridiculously hard to get these.

I had to have them specially delivered from like one of the few tiny farms left in the world that still grows them.

I mean, it's one banana.

How much could it cost?

$10?

Actually, that's not far off.

Anyway, they got a little banged up in shipping.

But let's see what the world's most hard-to-find banana tastes like.

(mysterious music) Wow!

(triumphant music) So much sweeter and more intense than any banana you find in a grocery store today.

Wow, it's just more banana-y.

This is what a banana's supposed to taste like.

It's just better.

We're really missing out today, I gotta tell you.

I'm gonna finish this and be right back.

(playful music) As the story goes, this is the banana that the banana flavor candies are based on.

It's got higher levels of isoamyl acetate.

That's the chemical that we associate with banana flavor.

That's why banana candy doesn't taste like the fruits you buy in stores today, because these bananas are basically extinct now.

See, back in the 1950s, a soil fungus nicknamed Panama disease began tearing through gros michel plantations, like the banana assassin.

The fungus would enter through the roots and plug up the plant's ability to drink water.

Now, like all commercial bananas, these are clones.

And since they're genetically identical, none of them had resistance to the disease.

Panama disease, definitely not a fun guy.

(audience boos) Anyway, by the 1960s, that disease had wiped out basically all of the world's gros michel plantations.

But bananas are basically the most popular fruits on Earth, so farmers did what anyone would do in their situation.

They found a different clone.

Enter the Cavendish banana.

They are not as banana-y as Big Mikes, but they ship well, and most importantly, they're resistant to the disease that killed Big Mike.

So it's what we have today.

Now we grow about 50 billion tons of Cavendish bananas, and shipped them around the world.

But unfortunately, that banana-loving fungus has evolved to munch on Cavendish bananas too.

Now, farmers and governments are carefully controlling its spread, but we could be on the cusp of another bananapocalypse, and bananas aren't our only problem.

Disease, pests, and climate pressures are affecting other seedless clones.

For example, the spread of citrus greening disease has slashed Florida's orange production by huge numbers.

Theoretically, we could use technologies like CRISPR to make our clones more resistant to disease.

But although it's likely a safe process, it's just not clear whether people would be comfortable eating CRISPR fruit.

In 2020, less than one-third of Americans felt that genetically modified food would be safe to eat.

But honestly, we might not have a choice, because our global food supply is its own maintenance trap.

Humans rely on just a few hundred varieties of fruits, vegetables, and grains in the global food chain, even though there are 30,000 edible plant species on Earth.

Humans have been playing with our food for thousands of years, it's kind of what we do, cultivating new varieties that are easier to grow, that are bigger, sweeter, more convenient, but the power to become biological gods comes with great responsibility.

I mean, every time we choose the perfect clone over genetic diversity, we're betting that we can outmaneuver Mother Nature to keep our food systems safe.

So maybe the biggest mystery of seedless fruits isn't how they got here.

It's how we'll keep them here in the future.

Stay curious.