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 nutritious potato. 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 known as the chili peppers. 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 domesticated spice ever 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, Ecuador, and Colombia. Over millions of years, it spread and diversified
throughout South America and eventually expanded north into Central America and Mexico By the time people arrived, the genus contained
dozens of wild chili species that were widespread throughout the region. 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 its seeds. 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 time. 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 at using water than non-spicy ones. 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 the distribution of the fungus. 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 of keeping food fresher, longer. 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 in southwestern Ecuador. And while our relationship with chilis was
clearly useful...and delicious, from an evolutionary perspective, it was never meant to happen. Because! 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 to disperse the seeds over a wide area. 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 to birds? Enter capsaicin. 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 a painful burning sensation 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 fire. 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 it insensitive to capsaicin. 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 the seeds far and wide. This is known as the Directed Deterrence Hypothesis,
and the trick worked well for millions of years... Until, of course, we came along, took a bite of a chili,
and thought to ourselves, “It hurts so good!” The rest is history. And a key reason that we learned to love the
pain may be because, in a sense, it kind of gets us high. 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 times.” 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 isn’t real. This is an example of a ‘constrained risk’
- where our body thinks we’re in danger, but our mind knows there’s no actual threat. The thrill of the experience and the rush
of chemicals that comes with it is pleasurable, and even kind of addicting - think horror
movies and bungee jumping. And this may be why our appreciation of chili
peppers and their heat generally increases with time and exposure. The more chilis, and the hotter ones that
you eat, the more you come to like them and tolerate ever-hotter varieties. The burning sensation doesn’t disappear,
but you increasingly associate the pain with the thrill of the experience
Only one other mammal is known to snack on chili peppers - a treeshrew. These little guys aren’t thrill-seekers
like us. Instead, their tolerance of the heat comes
from a mutation in their TRPV1 receptor that gives them reduced sensitivity to capsaicin
- much like birds. Their range overlaps with a plant in Southeast
Asia that has independently evolved a form of ‘spiciness’, so it’s thought that
this mutation helped the shrew expand its diet by side-stepping the ‘burning defence’. The same adaptation works on Capsicum too,
so the treeshrew will happily feast on chilis all day long. But, aside from that one exception, we’re
the only mammal that isn’t scared off by that burning sensation. And this wouldn’t be a very good love story
if Capsicum didn’t also get something out of the relationship too. From a certain point of view, Capsicum is
the real winner here - while their spicy defences may have originally evolved to keep us away
rather than to attract us, our infatuation with them has definitely worked out in their
favour. Without us being very weird heat-loving, thrill-seeking
mammals, it’s pretty unlikely that the genus would be as widespread as it is today. So, in a sense, becoming spicy was key to
its eventual global domination. After millions of years of seed dispersal
by birds, chilis found their new disperser of choice in the Holocene Epoch: a species
of Great Ape that would take them all over the world. Move over, birds, we are the seed dispersers
now. Now, we assisted chilis with their global
domination, but what about us? Find out more on our episode, “When We Took
Over the World”. And thanks to this month’s Eontologists
for being the spice of our life: Sean Dennis, Jake Hart, Annie & Eric Higgins, John Davison
Ng, and Patrick Seifert! You can become an Eonite at patreon.com/eons
to get fun perks like submitting a joke for us to read, like this one from Sarah M Why was the palaeontologist laughing? Because they found this humerus. And as always thank you for joining me in
the Konstantin Haase studio. Subscribe at youtube.com/eons for more evolutionary
escapades.
Now I'm craving to bite into a chili pepper for absolutely no reason lol
Currently vacationing in a rural area of Mexico for the next two weeks.
Freshly picked chiles, nopal, hand made tortillas, ripe mangos you pick from the tree, avocados so tender that you can eat with the skin on.
Life is good.
Edit: this variety of avocado is not available in the US due to its fragile skin and short maturity time.
Hot stuff.
That was interesting and informative. I learned a few new things!
Being tasty to humans is like winning the genetic lottery. We'll breed you and inflate your numbers (and therefore genes) to unprecedented levels.