This is Part 1 of the series Food for Thought (And for Eating), about science in the kitchen

Check out the recipe for chiles rellenos that accompanies this post.

Everyone knows that chile peppers can be hot. Some are almost inedible. But why do they taste hot? The answer: chile peppers wage chemical warfare on your mouth. Specifically, they contain a chemical called capsaicin, which is responsible for their ‘heat’.

The lanky molecular structure of capsaicin, the chemical that gives chiles their ‘heat’, and the active ingredient in pepper spray.

Capsaicin binds to the same pain receptors that send emergency signals to your brain when you take a swig of scalding hot coffee. So when you take a bite of five-alarm chili your brain thinks that you’re actually burning the inside of your mouth. And, as I recently discovered while cutting up habanero peppers, capsaicin can also make your brain think that you’ve lit your fingers on fire. But the effect eventually wears off, and there aren’t any long-term consequences.

In short, capsaicin is an irritant, which is why the ability to produce it evolved in chiles in the first place. In the wild, mammals don’t eat chiles because, apparently, they don’t like the burning sensation caused by capsaicin. Birds, on the other hand, don’t have the same pain sensory pathway as mammals, so they’re immune to capsaicin’s irritating effects, and they eat wild chiles all the time. But why do chile plants want to encourage birds to eat their peppers? And what do they have against mammals? The answer has to do with the chile’s seeds. While mammals tend to chew up the seeds along with the pepper, birds swallow the seeds whole, allowing them to pass through their digestive system none the worse for wear. This means that birds help chiles reproduce by spreading their seeds, while mammals often destroy the seeds. Over thousands of years this situation led to evolutionary adaptations that allowed chiles to produce capsaicin.

But this evolutionary strategy backfired when humans showed up. For whatever reason we humans can’t get enough of the hot, spicy flavor of chiles. Archaeological and genetic evidence suggest that wild chiles originated in Bolivia and gradually spread to their present range extending from the southern border of the United States in the north to the Caribbean in the east and the Amazon and the Andes in the south. Beginning about 6000 years ago chiles were one of the first crops that humans domesticated in the Americas, alongside corn and squash. When Europeans showed up  in the Americas 5500 years later, they quickly developed a taste for chiles as well. They began to incorporate chiles into European recipes as a substitute for expensive black pepper, which was imported from Asia at the time.

Habanero Chiles

Since then chiles have spread around the globe and have been embraced by nearly every culinary tradition in the world. But chiles are supposed to be irritating. So why do we love them so much? Other animals certainly don’t like them. Researchers have tried to develop a preference for chiles in rats by slowly introducing pepper flavoring into their food. But the rats continued to choose non-spiced food over chile-containing food when given the option.

An extensive 1980 study of chile preference in humans found that most young children don’t like chiles either – chile-lovers acquire the preference during childhood. The same study proposed that many people like eating chiles for the same reason they enjoy roller coasters or taking a very hot bath. These experiences are identified as “controlled risks” – they may trigger a negative physiological response but we know they are ultimately harmless. They offer a thrill. Even so, most people interviewed for the study claimed they liked chiles for their flavor or flavor-enhancing capability.

Further Reading

  8 Responses to “Some Like it Hot”

  1. This statement is incorrect: “In short, capsaicin is an irritant, which is why chiles evolved the ability to produce it in the first place.”

    This is a common mistake when talking about evolution. Evolution is not chosen; it is semi-randomly derived from current environmental needs based on their current genetic abilities (natural selection) + RANDOM mutations. No species chooses what it wants to evolve.

    • Thanks for the comment! You’re right – a species certainly can’t choose how it wants to evolve. I wasn’t trying to imply that chiles made a conscious decision to evolve the ability to produce an irritating chemical. Rather, I meant to say that the environmental pressures which I described later (birds distributing seeds and mammals destroying seeds) prompted genetic changes which allowed the plants to produce an irritant, capsaicin. This was an evolutionary solution to a particular problem. Sorry if that statement was misleading.

      • I’ve rephrased the sentence in a more precise way to eliminate any confusion about whether the chile plants had any say in their evolution. Thanks for the head up!

  2. Hey Dan,
    Thought I read your blog after hearing about it last night. This is a great post! Keep’em coming.

  3. It’s fascinating that the imperative to survive in these organisms had it “figure out” that mammals were chewing its seeds and developed the an irritant to deter them. Incredible!

  4. Your wright about evolution caused by au
    Long history of genetic accidentally positive change.
    Apples like the northern latitudes Because of the short lifespans Of winter kill on beetles leaving fast swallowing bears, moose and deer the sugary remains. Oranges grow in southern latitudes because their peal evolved D limonene which a natural solvent, surfactant, dispersion agent, and emulsifier all at the same time.
    Which turns boring insects in quickly suffocated. Also; cattle are an extremely successful species cause they taste good!!!

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