Name: Chilis如何变得辣（How Chilis Got Spicy (and Why We Love the Burn)）
Uploaded: 2021-05-03T04:25:13.000Z
Duration: 10 min 15 s
Description: 【看影片學英語】數萬部 YouTube 影片，搭配英漢字典即點即查，輕鬆掌握單字發音與用法，長久累積看電影不必再看字幕。

When the first people arrived in the Americas, they encountered many strange new species,

from armadillo-like animals the size of a car called glyptodonts, to the humble but

But they seem to have been struck by one group in particular - a genus of plant with the

bizarre ability to make mammals feel like their mouths are on fire: Capsicum, better

And starting about 6,500 years ago, archaeological and genetic evidence show that groups of people

throughout the Americas independently domesticated different chili peppers over and over again

This makes it one of the oldest known domesticated plants in the Americas, and possibly the oldest

While humanity's love affair with chilis has its roots in ancient Mexico, Central and

South America, they have now reached every part of the globe.

from their native home in the Americas to Europe, Africa, and Asia.

But how and why did chilis evolve this weird, fiery trick in the first place?

And why did we learn to love that spicy burn?

Well, like many of the best love stories, it happened against all the odds.

From an evolutionary perspective, our relationship with chilis was never supposed to be.

The story of chili plants and their unique red-hot fruit began in the middle of the Miocene 0:01:21.457,1193:02:47.295 Today, chilis are the most widely cultivated spice crop in the world - grown everywhere

Epoch, somewhere between 10 and 20 million years ago, when the genus split off from its

closest relatives and developed its characteristic spiciness.

Researchers think Capsicum originated in western or north-western South America, around Peru,

Over millions of years, it spread and diversified throughout South America and eventually expanded

By the time people arrived, the genus contained dozens of wild chili species that were widespread

Now, the fiery kick that many chili species are known for comes from a specific compound

unique to the genus called capsaicin, which is mostly produced in the tissue that surrounds

And exactly how these plants make capsaicin is still kind of unclear, but it looks like

a few of their genes went through a series of rearrangements and duplication events over

These duplications allowed the extra copies to evolve new functions, like making capsaicin.

But, producing this compound comes at a cost to the plant: it's a pretty large molecule

that requires valuable resources, like nitrogen, to create.

And some studies suggest that spicy chilis that make capsaicin seem to be much less efficient

This means that when there's less water available, like during a drought, spicy chilis

do much worse - like producing half as many seeds as their non-spicy relatives.

So, why did some chilis become spicy in the first place?

Well, there's evidence that the advantages of capsaicin may outweigh the costs.

The compound seems to protect the plant from certain insect pests and plant pathogens,

including a devastating plant-killing fungus.

Studies have shown that spicy chilis are much less affected by the fungus than non-spicy

ones, and the natural geographic distribution of spicy chilis matches up pretty well with

And, the fungus thrives in wet environments - exactly the places where the reduced water

efficiency trade-off that comes with being spicy is less of a big deal for the plants.

This antimicrobial trait of spicy chilis may have been one of the key reasons that people

were so quick to domesticate them over and over - they would've been a valuable way

And we have some archaeological evidence of this.

In 2007, researchers identified microfossils of starches from domesticated chilis from

seven sites throughout the Americas, always alongside microfossils of maize.

The oldest evidence of these two foods being associated goes back 6,100 years to a site

And while our relationship with chilis was clearly useful...and delicious, from an evolutionary

perspective, it was never meant to happen.

Another one of the probable functions of capsaicin was to keep organisms like us away.

Like many fruiting plants, the seeds of chili peppers are spread, or dispersed, by animals.

An ideal seed disperser, from the plant's point of view, doesn't have teeth that might

crush the seeds, has a digestive tract that doesn't destroy them, and has the ability

For chili peppers, that meant birds were the best candidates.

So early chili pepper plants faced a challenge: how could they keep other animals, like mammals

with seed-crushing teeth and small dispersal ranges, away, while still being attractive

You see, this compound binds to a receptor in mammals called TRPV1.

This is an ancient receptor that appeared early in the evolution of vertebrates - over

400 million years ago - and is widely shared among vertebrates living today.

Its function is to sense dangerously high levels of heat and warn the organism by stimulating

Through an oddity of biochemistry, capsaicin is also able to activate this receptor, which

tricks mammals, including us, into feeling like their mouths, stomachs, or skin are on

It doesn't actually cause any physical damage - it's just a sensory illusion created by

hacking an ancient pain pathway shared across many different species

But the same heat-sensing receptor in birds has small structural differences that make

This means that while mammals quickly learned to stay away from this group of irritating

fruits, birds remained completely unaffected, and continued to eat the fruit and disperse

This is known as the Directed Deterrence Hypothesis, and the trick worked well for millions of

Until, of course, we came along, took a bite of a chili, and thought to ourselves, “It hurts so good!”

And a key reason that we learned to love the pain may be because, in a sense, it kind of

When TRPV1 is triggered by capsaicin, your nervous system is completely fooled into perceiving

dangerous levels of heat and sends a message like:

“Hey you, so….uh.….some bad news - you're on fire right now.

No worries...sending some chemical relief your way to help you through these trying

Levels of two neurotransmitters suddenly rise - endorphins, which help to reduce pain and

stress, and dopamine, which gives a sudden rush of pleasure following the initial pain.

Their rapid release makes eating hot peppers a sensory rollercoaster - one that potentially

becomes enjoyable, you know, once you've been through it a few times and realized that the danger