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 plants with the bizarre ability to make mammals feel like their mouths is on fire: Capsicum, better known as chili peppers.
About 6,500 years ago, archaeological and genetic evidence showed that groups of people throughout the Americas independently domesticated different chili peppers repeatedly. 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 roots in ancient Mexico and Central and South America, they have reached every part of the globe. But how and why did chilis evolve? Why did we learn to love that spicy burn?
Why are peppers spicy?
The answer lies in a tiny molecule called capsaicin, which naturally occurs in chili peppers. It can trigger an intense burning sensation. Chilli peppers, like apples, bananas, and raspberries, are fleshy fruit that plants develop after fertilizing.
Chilli peppers are no exception to the eat-travel-poop method of seed dispersal. The ripe fruit’s bright reds, yellows, and oranges are needed to attract passing creatures. But they hide a vicious secret. Most fruits of the Capsicum genus, chili peppers, contain the burn-inducing chemical capsaicin, lying in wait for unsuspecting snackers.
Researchers have found that both mammals and insects experience the heat of capsaicin when it comes into contact with the insides of their mouths. It makes them avoid the deceptive fruits of the Capsicum genus. Capsaicin is a colorless, odorless substance most heavily concentrated around the tissue of a pepper. It gives you that mouth-on-fire feeling when eating something spicy.
Capsaicin is not hot. Hot peppers are not hot, at least not of a thermal persuasion. We perceive them as being hot. So, capsaicin in hot peppers or spicy foods binds to TRPV1 receptors in the mouth and other tissues in your body.
This pain receptor detects hot substances like boiling water or piping hot food and acidic and bitter substances. It could cause damage to ours. But capsaicin molecules fit into TRPV1 receptors. When eating something with capsaicin, the capsaicin binds to the TRPV1 receptors of neurons in the mouth. It sends a neural signal to the brain. It tells us we’re eating something that we shouldn’t be.
Capsaicin is perceived as a pain-causing that sends chemical signals to the body to get this out of the system. When we eat something spicy, our noses start running, tears streaming from our eyes, and we want to drink something cold.
The higher the capsaicin in a pepper, the more binding to your TRPV1 receptors. The more intense your reaction is to that pepper. It is measured on the Scoville scale. The capsaicin binds to TRPV1 receptors all over the mouth and feels like you’re on fire. Capsaicin has an end with a long hydrocarbon tail. It means it’s nonpolar. Nonpolar molecules dissolve in other nonpolar substances.
Water is a polar substance, so drinking water after eating a hot pepper is like mixing oil and water. It won’t work out that well. Water will spread the capsaicin around the mouth, intensifying the pain. But milk contains nonpolar molecules, so the capsaicin will dissolve in the milk and wash out of your mouth, giving you sweet, sweet relief.
In addition to their nonpolar powers, dairy products contain the protein casein, which attracts capsaicin molecules. So milk or ice cream actively pulls the capsaicin molecules off your TRPV1 receptors and dissolves them.
Why do we like spicy food?
Capsaicin 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. Its function is to sense dangerously high heat levels and warn the organism by stimulating a painful burning sensation. Through an oddity of biochemistry, capsaicin can activate this receptor, which tricks mammals into feeling like their mouths, stomachs, or skin is on fire.
It doesn’t cause any physical damage. It’s a sensory illusion created by hacking an ancient pain pathway shared across many different species. But the same heat-sensing receptor in birds has minor structural differences that make it insensitive to capsaicin. When TRPV1 is triggered by capsaicin, your nervous system is completely fooled into perceiving dangerous heat levels and sending a message. It also sends some chemical relief to help.
- Two neurotransmitters suddenly rise, and endorphins help to reduce pain and stress. Dopamine gives a sudden rush of pleasure following the initial pain.
Their rapid release makes eating hot peppers a sensory rollercoaster that potentially becomes enjoyable. It is an example of a ‘constrained risk’ where our body thinks of danger, but the mind knows there’s no actual threat. The thrill of the experience and the rush of chemicals that come with it is pleasurable.
The burning sensation doesn’t disappear, but you increasingly associate the pain with the thrill of the experience. Instead, their heat tolerance comes from a mutation in their TRPV1 receptor, giving them reduced sensitivity to capsaicin, much like birds.
How do peppers become spicy?
Our relationship with chilis was never supposed to be from an evolutionary perspective. The story of chili plants and their unique red-hot fruit began in the middle of the Miocene Epoch, between 10 and 20 million years ago. The genus split off from its closest relatives and developed its characteristic spiciness.
Researchers think Capsicum originated in western or north-western South America, 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 had contained dozens of wild chili species widespread throughout the region.
The fiery kick that many chili species are known for comes from a compound unique to the capsaicin genus. It is mainly produced in the tissue that surrounds its seeds. How these plants make capsaicin is still unclear.
But it looks like a few of their genes underwent 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 large molecule that requires valuable resources, like nitrogen, to create.
Some studies suggest that spicy chilis make capsaicin seem much less efficient when using water than non-spicy ones. It means that when there’s less water available, like during a drought, spicy chilis do much worse, producing half as many seeds as their non-spicy relatives. So, why did some chilis become spicy in the first place?
There’s evidence that the advantages of capsaicin may outweigh the costs. The compound protects the plant from insect pests and pathogens, including a devastating plant-killing fungus. Studies have shown that spicy chilis are much less affected by the fungus than non-spicy ones. The natural geographic distribution of spicy chilis matches up pretty well with the fungus distribution.
The fungus thrives in wet environments, exactly the places where the reduced water efficiency trade-off. 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 people quickly domesticated them.
They would’ve been a valuable way of keeping food fresher and longer. We have some archaeological evidence of this. The oldest evidence of these two associated foods goes back 6,100 years to southwestern Ecuador. In contrast, our relationship with chilis was valuable and delicious.
From an evolutionary perspective, it was never meant to happen. It’s 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 doesn’t have teeth that might crush the seeds from the plant’s perspective. It has a digestive tract that doesn’t destroy them. It can disperse the seeds over a wide area.
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“Chili pepper.” Germplasm Resources Information Network (GRIN). Agricultural Research Service (ARS), United States Department of Agriculture (USDA).
Dasgupta, Reshmi R. “Indian chilli displacing jalapenos in global cuisine – The Economic Times.” The Times of India.
“HORT410. Peppers – Notes”. Purdue University Department of Horticulture and Landscape Architecture.