If you've ever taken a bite out of a habanero you might think the purpose of its spiciness it's pretty 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 that.
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 pepper 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 well 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 it's led scientists in the 1980s to suggest that spiciness evolved for that reason an idea known as the direct deterrent hypothesis.
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 that mammalian guts often reduce viability of the seeds while bird guts don't so ideally a pepper plant once 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 a chemical defense against mammals some lab and field studies supported the idea that,
spiciness evolved as a deterrent because rodents and other mammals just don't really seem to like eating spicy peppers 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 well I'll take the extra spicy in them 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 Ruiz had four rats eat spicy food for two weeks while five other rats didn't afterwards when given the choice to return to a non spiced diet three of the four rats in the first group stuck to the spiced meals and one of the five 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 of varies probably because producing capsaicin costs the plant in other ways.
If they can get away with being bland they stopped making it when scientists have surveyed wild pepper plants in places like Bolivia where both mild and hot peppers grow natively they 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 that capsaicin effectively stops its growth we're 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
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 are 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 when 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 next time you dig into a nice plate of Szechuan or vindaloo rest assured that the burn probably isn't meant for you it's just the lovely taste of chilly pesticides.
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