The Real Reason Peppers are Spicy

The Real Reason Peppers are Spicy

If you’ve ever taken a bite out of a habanero,
you might think the purpose of its spiciness is obvious. Eating it hurts. A lot. So for a plant, spice is a great way to tell
us to not eat that. At first, that’s what scientists thought,
too: that pepper plants evolved spiciness to deter mammals like us from eating their
fruits. Joke’s on them! But careful research on wild peppers suggests
that’s actually a secondary benefit at best. The real reason peppers are spicy probably
has more to do with defending against much smaller dangers, like insects and mold. The main compound that makes peppers spicy
is capsaicin. It binds with special heat-sensing receptors
on your nerves, which is why spicy peppers feel like they’re burning you. And while lots of people like eating spicy
foods, it’s not usually because they enjoy the painful feeling that comes with biting
into a raw hot pepper. For the most part, other mammals don’t like
the pain, either. Which led scientists in the 1980s to suggest
that spiciness evolved for that reason—an idea known as the direct deterrent hypothesis. When this hypothesis has been put to the test,
it’s largely held up. Plants generally produce fruit to encourage
animals to eat them and spread the seeds around in their poop, but some animals are better
seed spreaders than others. For pepper plants, it turns out mammalian
guts often reduce the viability of the seeds, while bird guts don’t. So ideally, a pepper plant wants its fruits
to be eaten by birds but not by the likes of us. Birds’ heat-sensing nerves aren’t sensitive
to capsaicin, so it seems like a perfect choice for chemical defense against mammals. Some lab and field studies support the idea
that spiciness evolved as a deterrent, because rodents and other mammals just don’t really
seem to like eating spicy peppers. But that’s not always the case, which has
led researchers to question if the direct deterrent hypothesis is right. For example, we know that spiciness doesn’t
stop humans from eating hot peppers, partly because we can develop a tolerance for increasing
levels of heat. Partly because, apparently, we love pain! Or just showing that we can! We’re like, “I’ll take the extra spicy!” And then it’s the Thai restaurant and you’ve
made a huge mistake… And it turns out that other mammals can appreciate
spiciness, too. In a study published in 1990, researchers
had 4 rats eat spicy food for two weeks while 5 other rats didn’t. Afterwards, when given the choice to return
to a non-spiced diet, 3 of the 4 rats in the first group stuck to the spiced meals And 1 of the 5 that didn’t have the spicy
stuff went over to the spicy stuff! That’s a small study, and it’s nearly
30 years old, but it does suggest that some mammals are okay with a little heat, and maybe
would even learn to eat spicy peppers if surrounded by them. But the biggest blow to the direct deterrent
hypothesis comes from studies of the natural variation in pepper spiciness. In wild populations, the spiciness of a given
species varies, probably because producing capsaicin costs the plant in other ways. So if they can get away with being bland,
they stop making it. When scientists have surveyed wild pepper
plants in places like Bolivia, where both mild and hot peppers grow natively, they’ve
found that mammals don’t tend to eat the peppers — not even the mild ones. Plus, peppers don’t tend to be more spicy
when there are more mammalian plant-eaters around to eat them. So mammals don’t seem to be a big concern,
even for the non-spicy plants. Instead, spiciness is associated with local
climate: spicier peppers grow in areas with more rainfall. And scientists have found that more than 90%
of wild plants have signs of fungal damage. So in the late 2000s, scientists started to
think that mold, not mammals, might be the real reason for spiciness. One fungus in particular has proved devastating
to wild peppers—researchers found it was the only significant cause of damage to fruits
and seeds of Bolivian peppers prior to dispersal. When insects make holes in the peppers, they
create tiny scars that are associated with infection, probably because they give the
fungus a foothold. But capsaicin effectively stops its growth. Where both spicy and mild varieties of the
same pepper grow, spicier peppers are much less likely to be infected. And researchers have found that the more scars
you find on peppers in a given area, the spicier they tend to be — probably because they
need more protection from the fungus that can grow in all those scars. Capsaicin is a decent bug repellent, too. All this suggests that spiciness really did
evolve to deter insects and kill fungi — and if so, that also explains why pepper fruits
get hotter as they mature. Most fruits have gross-tasting compounds in
them early on, which is thought to prevent critters from eating them before the seeds
are ready to be spread. Once they’re ripe, those compounds mostly
disappear, inviting seed-spreading animals to feast. Peppers exactly the opposite—they get spicier
as they ripen. And if the spice is meant to deter mold, that
makes sense. There’s no point where the plant can let
down its guard against mold, because the fungus can—and will—attack no matter how big
or small the pepper is. And riper fruits represent more investment
by the plant, so the absolute worst time for a fruit to become spoiled is right when it’s
finally ready for its seeds to be dispersed. So that increase in spiciness over time is
another point in favor of the idea that it probably evolved as a defense against insects
and the fungi they facilitate. Researchers think that if mammals are also
discouraged from eating them, it’s probably more of a helpful side bonus. So the next time you dig into a nice plate
of Szechuan or vindaloo, rest assured that that burn probably isn’t meant for you. It’s just the lovely taste of chili pesticides. Thanks for watching this episode of SciShow! If you love eating the hottest peppers in
spite of the burn, you might like our episode on how spicy food might be good for you—independent
of its antimicrobial action.


  1. Could it be both? Afterall natural selection doesn't think. All that matters is whether a given organism successfully reproduces (and its offspring can do the same)

    Mammals give spicy plants a reason to be mildly spicy, since mammals will leave them alone then. After that there's no incentive to evolve to be yet spicier without fungus. But there would still be an incentive to get to the point of being mildly spicy from mammals.

    As for rats coming to prefer spiciness, maybe it's because rat brains get the same endorphin response that humans do, so when researchers subject them to intense circumstances they develop the same response.

    Apparently, rats are capable of masochism, and if you think about it enjoying spicy food is a mild form of masochism. Here's a link to a study where rats chose to be electrically shocked.

    In evolution there may be cases where not doing something because of pain leads to a disadvantage, in which case natural selection doesn't care whether this is resolved by not feeling pain or as much pain or turning the pain into pleasure. Or more accurately it can care. If the pain is intense enough without the pain being experienced as pleasure then conceivably it would be easier to just evolve to like the pain than to evolve not to feel it as much. Especially for social animals like humans and rats where complexity can change survival needs several times during life being able to learn to love pain under certain circumstances (such as acquiring a taste for spicy food or enjoying the rush from heavy exercise) while still abhorring it under other circumstances could be beneficial.

  2. I believe our taste buds are evolved to reward us for eating a well balanced diet. Things eaten too often become bland and boring signaling us to seek out other foods so we do not suffer from nutritional deficiencies.

  3. I twice conquered the Blazin Buffalo challenge at Buffalo Wild Wings during the time they were using ghost pepper sauce. After my second win, I went on to order a second round just to enjoy!

    My wife cant even handle tobasco :/

  4. could i get that capsaicin or whatever scares of the insects in bottle or spray form? that could be useful…also does that apply to spiders as well?

  5. Wrong, in mexico the point of putting as much chilli as possible to food is for that burning painful feeling..

    Bolivian chilli?, weak, those researchers should come to mexico and check the 300+ species of chilli plants..

    Also wrong again, not all the chilli plants tribe in rainforest environent, i live in a semi desertic area, and there are many chilli plants that grow quite fine..

  6. Can you do a follow up?

    How come Fresh/natural foods with a lot of peppers don't mess up my digestive system as much as fast food with artificial spices and extracts?

  7. I am a big fan of habaneros. I really like the flavour which can be great add to sauces without necessarily making it to spicy, and find that heat level is enjoyable in most dishes where it's more concentrated. Scorpions are pretty good, but I really don't like ghost peppers, I find the taste rather harsh.

  8. I've noticed that you pronounce the first I in capsaicin. You might be the only person I've heard to pronounce it.

  9. Before video: so people won’t eat it.
    After video: I have learned something new, but why not use something that deterred those things without being spicy? Why does naciasin have to be spicy?

  10. Hank why is it that peppers are spicy coming out (also cause stomach aches) but not for birds stomachs or intestines.

  11. I like the flavor of it it’s hard to explain it just good like a high feeling of flavor like a burst of flavor idk(Edit) if you get past the heat

  12. We love pain, or just showing that we can and: I will take the extra spicy and then its the thai restaurant and you have made a huge mistake.
    This hit close home. Hilarious. JAJAJAJAJAJAJA

  13. In my suggestions as I was currently complaining about my burrito being to Spicy, stop watching me F.B.I

  14. Wait peppers are spicy … I think there is something wrong with my taste buds

    Or maybe it’s because I’m Mexican

  15. It’s always about the peppers and their capsaicin when we talk hot. I’m curious about the burn from horseradish and wasabi, which is a more nasal burn. Google tells me that allyl isothiocynate is the culprit. So any research on why mustards burn?

  16. So, the implication here is that capsaicin is a fungicide. Is this being explored for possible medical and/or agricultural use? A natural fungicide would seem to be beneficial in both areas.

  17. So if you eat a lot of spicy hot food, would musquitoes bite you less if they can choose from you and few other humans ?

  18. Even the hottest peppers still get that black mold inside them (During pollination), apparently the spores work their way down the stigma (Where the pollen goes down), this can lead to dwarf fruits, but can happen to full sized fruit also. but I find that earwigs attack (Drill holes into and breed inside) my Bell, Jalapenos more than my Habanero, Reapers.

  19. My question is why can't we digest the spiciness completely when we eat a particularly spicy food? you eat something hella spicy and you're gonna regret pooping it out

  20. An advice for people who wants to enjoy hot spicy food but don't want to suffer the consequences of "burning" stomach or stool that may come along with itchy anus: drink milk, before eating to line your stomach and/or after eating to wash down the capsaicin.

  21. As mentioned in the video; birds dont react to the spicy chemical! You can feed a bird the spiciest pepper and they wont care!!! I’d try it myself, but my bird seems very picky about its veggies to begin with.

  22. Speaking of peppers, I've been seeing a post going around about how bell peppers have 2 genders and you can tell the difference between them by counting the bumps. I think a lot of people legitimately believe this and don't understand anything about botany! This might be a good video topic!

  23. i knew some horses that liked hot sauce. its a trick that will usually (but not always) get a horse to stop chewing on their stall…

  24. Peppers: Ha! Through years thousands of years of evolution we have developed a defense mechanism to deter you from eating us!

    Humans: Mmmm tasty and exciting.

    Peppers: Am I a joke to you?

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